Re: Topband: Ethics and the Individual

[Tom W8JI]

You conveniently clipped off the part where I said  "as long as it hurts no 
one else".


Don't  play stupid games with me by rewording what I say and posting it in 
public to make it look like I said something I did not. Also, don't lecture 
me about ethics after that stunt.




- Original Message - 
From: "Larry Burke" 

To: 
Sent: Saturday, January 16, 2016 8:10 AM
Subject: Topband: Ethics and the Individual



The ethics are limited to following the rules, and what a particular

person decides to do beyond the rules is up to the individual



Martin Shkreli would be proud of this argument. Increasing the price of
Daraprim 5000% did not break any rules either. And, hey, he didn't hurt
anyone or infringe on their rights -- they were sick already and if they
wanted to get better the drug was available to them. It's the ultimate
pay-to-play.



- Larry K5RK





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Re: Topband: strange propagation

[Tom W8JI]

This reflector has gone down the toilet with personal BS that serves no 
purpose except to pick fights.


After 20 years, I'm leaving it.It sure went down the tubes.


- Original Message - 
From: "Louis Parascondola via Topband" 

To: ; 
Sent: Saturday, January 16, 2016 7:24 AM
Subject: Re: Topband: strange propagation



That was not nice.


Lou W1QJ



-Original Message-
From: Roger D Johnson 
To: topband 
Sent: Sat, Jan 16, 2016 7:09 am
Subject: Re: Topband: strange propagation


Sounds a lot like the RHR folks!




A friend of mine at the Georgia State Public Service Training Center 
(right
down my street) says this social trend, made pandemic through Internet, 
has
even been assigned a name now. It is called Homogeneous Clustering. This 
is
where groups of people cluster together and invent their own reality, 
feed off
each other's emotions, and dismiss anyone outside their group as a 
problem and

dishonest.


73 Tom
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Re: Topband: strange propagation

[Tom W8JI]

I can't be 100% sure but I think this will all wash down to the fact that 
stations are no longer licensed and the control operator is fully 
responsible.  And I do believe that is the case.  RHR has lawyers on 
retainer and I'm sure this has been legally looked at.  I can get the 
ruling they go by.




This all comes up every time with this subject. I don't know why people have 
such a difficult time remembering it. Like politics today, we can't let 
facts get in the way of hyperbole. It is also more fashionable to hate and 
complain than offer any viable solution. It is always all about the insults 
instead of solutions..


Starting way back about 35 years ago, we no longer had station licenses. We 
no longer had to sign mobile, tell the FCC where we were at if out of local 
district, and no longer had to sign portable. Station licenses were gone as 
long as we were in the continental USA.  The license is with the control op.


About the same time, location or station for DXCC also changed and did not 
matter. DXCC went with the call, not the location.


It was also never illegal to make money from property in a station, it was 
only illegal to charge for the service of communication or use 
communications to augment business communications. People have been renting 
stations and equipment for years and years, and people have "made money" 
since the very first copper wire was sold.


The proper way to handle this, if people disagree with the rules, is to work 
to have the rules changed. I would suggest, however, things get thought 
through very carefully. It would be very easy to kill or seriously damage 
the hobby with poor changes.


It seems to me the real problem is people want an award for DXCC 
specifically to how they operate and live, and everyone has to fit that 
criteria.


To me, that makes absolute sense for three tiers.

1.) You cannot use a club station, you cannot move, you cannot phone a 
friend. This would be a STATION and operator DXCC.


2.) DXCC to the station no matter who the op.

3.) DXCC to the no matter what the station. This is what we have now.

Instead of whining like two-year-olds about what the FCC rules are, because 
the FCC will never roll back to making us have specific station locations, 
the real solution is in what the DXCC rules are. The award rules will not be 
changed here, and it is very unlikely the ARRL with yank DXCC's from people 
who have worked DX from more than one location, so the best approach would 
be a new DXCC with all contacts allowed from one location, where it is the 
licensee's station and operating.


73 Tom 


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Re: Topband: strange propagation

[Tom W8JI]

I would think a few fines issued by the FCC to the remote station holder,
would shut these games down in a hurry.  I wonder if the RHR station 
owners

that are being leased out by individuals realize their liability in these
circumstances.  I think some people will be shocked with a certified 
letter

at some point and the game will quickly change.


Ed,

This horse gets beat to death every several months.

RHR is the safest, most regulated, use of a remote station. IP's are 
watched, people pay a membership, they have to log in, and they know if 
caught breaking any law they lose a deposit and are booted. It is also 
completely 100% legal.


In contrast, there are dozens of hundreds of unregulated free Internet 
stations. No one thinks about them, but they are all over the world now.


I don't have the slightest worry about RHR leasing my station, because I 
know they watch it. I also know it is their responsibility to watch it, but 
the main thing is it is policed by them.\


This entire thing is beyond silly. A group of the same repeating people 
without facts just stir each other up with fantasies, which is typical for 
people today. This is why we can't fix anything. We never let logic or facts 
get in the way of whining like two-year-olds.


A friend of mine at the Georgia State Public Service Training Center (right 
down my street) says this social trend, made pandemic through Internet, has 
even been assigned a name now. It is called Homogeneous Clustering. This is 
where groups of people cluster together and invent their own reality, feed 
off each other's emotions, and dismiss anyone outside their group as a 
problem and dishonest.


Political parties are now largely homogeneous clusters, as are protest or 
action groups. I hate to see Hams, who generally used to be higher than 
average intelligence, develop homogeneous clustering. It looks like that is 
happening. Next thing you know, the false memes and quotes will start.  :)


73 Tom 


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Re: Topband: strange propagation

[Tom W8JI]

RHR has stated that they require operators to operate "ethically" on their
network. Exactly how to they define that term?  Is it considered ethical 
for
a ham in, say, Huntington Beach CA to call -- via a commercial remote in 
New

York -- a station at the United Nations on 6m when the only propagation at
the time is ground wave?



If you don't like the rules of an award, I suggest you work to modify the 
award or create a new award.


This may come as a real shock, but you are going to have a very difficult 
time changing the world to fit your particular feeling or idea of how you 
think the world should be, without changing the actual rules.


It cannot matter less what you think other people should do. The ethics are 
limited to following the rules, and what a particular person decides to do 
beyond the rules is up to the individual (as long as he infringes on no one 
else's rights in the process). That might even be a good way to run a 
country.


If a few people spent half the time they do whining and complaining working 
on a new award or changing the award, the problem could have been fixed 20 
years ago.


My belief is the real hobby for some is being unhappy with not being in 
charge of everyone else. They don't want the problem fixed, because then 
they would have nothing to get all stirred up about.


73 Tom 


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Topband: FCC regulations circa 1960's

[Tom W8JI]

I'm almost certain that all of his serious DXing was done from the water
tower location.  He also had a 160m station at his home, but it was on a
very small urban lot and as I recall, he had only a low dipole up for 160m
there.

Whenever I heard him operating from the water tower site, he would sign
W1BB/1 to indicate portable operation but I guess that was required back
then.




That's correct, if you think back we assigned a station address and a 
operator address on our licenses. Today, we only have an operator contact 
address. There is no station location or license location except as defined 
within this boundary:


(1) Within 50 km of the Earth's surface and at a place where the amateur 
service is regulated by the FCC;
(2) Within 50 km of the Earth's surface and aboard any vessel or craft that 
is documented or registered in the United States; or


(3) More than 50 km above the Earth's surface aboard any craft that is 
documented or registered in the United States.


Our station license covers the entire jurisdiction of the FCC, rather than a 
street address like it did in the 70's and earlier and it is any radio we 
control. Thus we no longer need to sign / district  or mobile, or report to 
the FCC when we are going to operate away from home more than a certain time 
or distance.


The station location license is gone. It is now everywhere the FCC controls 
as one big location, anywhere we control a radio.


Stew had to sign /1 because at that time station licenses were location 
specific. There was no station license assigned to the water tower address. 
He was legally required to use /1.


If there was a station license there, like W1XX, it would have been W1XX. 
Not W1BB.


What I'm not sure of is operating above the class of the a station location, 
prior to the elimination of the station license we used to get (I think it 
was listed at the top of the license as "transmitter location or authorized 
remote location" ). Mine always said "same as below" :-) .


Does anyone recall that rule? I know remote control locations had to be 
licensed, but what was the identifier when using another Ham's station who 
had lower license class but a station license assigned to that address?


73 Tom




unless Stew's class allowed operation outside that station license class. 
Then it would have been both calls, but I can't recall if it was W1XX/W1BB 
or the other way. 


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Re: Topband: Strange propagation

[Tom W8JI]

I am a 160 card checker, and I damn well DO check the times!  I'm sorry
to report that I have found cases where "impossible" QSOs were claimed,
and reported them to the mother ship in Newington.  I would sincerely
hope that my colleagues would do the same.>>>

But isn't it legal to operate anywhere in the lower continental USA to make 
a DXCC contact in the lower continental USA?


As far as I know, they made that legal many years ago, and the contact 
simply has to be made from the USA lower 48 no matter where.


Where were all the complainers when they did that? As far as I'm concerned, 
that was the end of DXCC meaning very much. I wrote and complained. Now it 
is what it is.


73 Tom 


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Re: Topband: 4 square

[Tom W8JI]

Used both the 4 square and 8 circle array by DX Engineering. Both work 
but, in my thunderstorm environment, I spent many hours and as many 
dollars as the systems originally cost repairing them over three seasons. 
This is despite keeping the systems powered off, except when being used. 
The guys at DXE said doing so would protect the systems. Unfortunately 
that proved not to be the case at my middle Tennessee qth. Steve, NN4T




Whoever said that probably had good intentions, but unfortunately that is 
false.


No matter where you are located, off or on makes an immeasurable difference 
in likelihood of lightning damage.


You really have to find out what is being damaged and where the ground loop 
causing the problem is your system. It should be curable to a large extent, 
but not by simply turning it off. That makes almost no difference for 
lightning. 


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Re: Topband: RE; Ground screen Question

[Tom W8JI]

His reinforcing steel inside his driveway is probably way far
out of the realm of Ufer grounds, due to it being small gage
conductors. Aside from the great difficulty of boring into the
concrete and adequately bonding to those wires, I wouldn't try
this anyway out of concern that the current density during a
major lightning hit might be sufficient to produce widespread
cracking of the concrete.


If it was the sole ground, or the major part of a ground that might have to 
handle a direct hit, I wouldn't use it.


If it were simply something to augment an already good lighting ground or 
improve an RF buried ground system, I would not worry one bit about using 
it.



Now I'll have to go re-read and brush up on Ufer grounds, but
as I remember, his driveway setup would be woefully inadequate
for the possible current levels involved in the event of a direct
lightning strike. Personally, I wouldn't go there. A concrete
drive would be a little pricey to replace, especially considering
the relatively small prospective gain in HF ground quality he
might see by connecting his radial field to it. I'd much rather
connect *over* that drive using strategically sawed grooves
and lightly concreting in a few wires at the surface in a few
places- this assuming he has somewhere to go on the far side of
the drive with those wires anyway.


Again, it is only a problem if that is the major part of the ground. If it 
is incidental and only an additional improvement, and the rests of the 
system was OK without it, I'd use it.


I've tied my heating ducts and water pipes in, in the past.  It does take 
some common sense in whether it is worth the work, and knowing if the rest 
of the system is large enough that it creates no hazard.



I know a ham who thought his well pipe might make a dandy
addition to his ground radial system. He connected it, and
eventually had to replace a 600 dollar well pump after a strong
lightning hit on his property. This driveway question reminds me
of that. Properly designed Ufer grounds, fine- but I sure don't
want to invite lightning hits to dissipate through anything
concrete on my property. My two cents (two dollars, adjusted
for inflation...)


That is just asking for problems. Many well pipes are only metal at the 
head. Below the head or cap, they are often plastic. Well casings are almost 
always plastic today. The only guaranteed metal paths are the wires to the 
pump, even if it starts as metal at the top. Also, the wires are outside any 
metal pipes if metal pipes do exist, and lighting travels on the outermost 
surfaces. That would be the wires.


The well is nothing like concrete remesh. I would not bother connecting to a 
unknown rebar system, but if I knew it was bonded or remesh (screen) I sure 
would use it. Not as a primary ground, but to augment an existing pretty 
good ground in a direction the existing ground might not go.


I remember a few people who had houses in the way of a full system, and they 
ran the radials right under the floor joists. They used heating ducts, 
fences, water pipes, and everything else they could. The more they used, the 
stronger they got.


73 Tom 


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Re: Topband: Received Signal Strengths

[Tom W8JI]

Typically, on 160M, I leave the preamp off for my beverages. The received
noise floor for my N/S beverage (on CW) is usually S2 - 3 and for my 
phased
EU beverages is S0 to S1. I have found the signal strengths of the 
received
stations to be 1 to 2 S units down on the beverage and equal or stronger 
on

the beverage if I turn the preamp on - with usually a rise in the noise
floor by a 1 or 2 S units. Interestingly, on 80M CW, I usually use the
beverage preamp. The signal often comes up 3 - 4 S units and the noise 
only

1 to 2 S units. I often drop in some attenuation to make the noise floor
"just" go away.

If the signal comes up 3-4 S units and the noise 1-2 S units, the meter is 
nonlinear. This is typical for many receivers. Some are as little as 1 dB 
per S unit down low on the scale.  Most meters (it was years ago I looked) 
were 3 to 5 dB per S unit up at the high scale end.


The entire idea of S readings is for many uncontrollable reasons.. 
meaningless.


There have been various campaigns over the years to correct reports, but 
none can ever mean anything.


It is silly getting all worked up because we **think** S meters and S 
reports are like precision dial calipers, when they are really like marks on 
a rubber band. 


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Re: Topband: Received Signal Strengths

[Tom W8JI]

marks on a rubber band.



Great analogy Tom.If I were truthful with the signal reports for most 
of

the topband DX worked here, using the S-meter with RX loops, I would be
sending "209".


I don't know how to really express it, but our S meters have index marks 
that say the same thing but all read (because of many variables) different 
things.


It's like have voltmeters where on some meters 1 volt is .529 volts and on 
others one volt is 8.7 volts. It isn't just the receiver (which are poor 
enough), it is the IF filter, local noise, antenna gain, and everything 
else.


If we dispense with the S meter and go by ear, it can get even worse. I 
don't anyone who can listen to a receiver without looking at an S meter and 
tell levels from one through nine based on sound.


Why anyone would criticize other people or contests for something we should 
all know is either next to meaningless at worse, or cannot ever be accurate 
at best,  is beyond my comprehension.


If you like the guy, give him an S9. If you don't, tell him he is S1. 


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Topband: W1BB (NOT K1BB, whoever that is)

[Tom W8JI]

I remember this stuff well from the early 1960's. I got my feet wet in 160 
because it was a hotbed for local mobile and ragchew activity in the Great 
Lakes area.


Stew, W1BB, was "famous" on 160 because Stew was the main organizer and main 
promoter of all 160 DX work, including trans-Atlantic tests.


The trans-Atlantic tests were on weekends during DX season, generally at 
Europe sunrise Sunday mornings 0500Z-0730Z on "Saturday midnight" USA, where 
USA stations called CQ on the first and odd 5 minutes and Europe and DX CQ 
the second and even 5 minutes working split. This was because of LORAN, USA 
could not transmit above 1825 and Europe below 1825. There were other tests, 
but these were the popular ones.


Stew also led in the DX chase toward 100 countries, which was very difficult 
back then because antennas were poor, equipment poor, and power levels 
severely limited. 160 was limited to as little as 25 watts dc plate input 
power in certain band sections and hours, which was maybe 12 watts output. 
(In 1983 Amateur power measurements changed to RF output power, instead of 
power amplifier DC input power.)


There were several very active DX'ers on the east coast in the early 1960's, 
some calls were W1HGT, W2EQS, and W2IU,  with W8FPU and W8GDQ active from 
Ohio.


It was an entirely different world in the 1960's because of technology, 
LORAN mandated band segments (25kc wide in the USA), and power levels.


Police and radio location used the area between 1600-1800 kc/s, I used to 
listen to the Cincinatti police at night on an opened up AM BC receiver 
around year 1960. The Great Lakes was also full of radio navigation 
transmitters in the area below 1800 and above the upper end of the AM band 
at 1600 kc/s.


73 Tom 


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Re: Topband: Using shielded CAT5 data cable as feedline foractive antenna; benefits of multi-turn K9AY loop/SAL/etc?

[Tom W8JI]

Sounds like you, Tom, and LZ1AQ are saying the same: in order for loops to 
be effective (low SNR and high signal levels), they must have large area 
and low reactance (inductance to be exact). Parallel loops or fat conduits 
increase the signal levels, while the CP configuration and other similar 
measures are aimed at lowering the loop's inductance. All this of course 
is paired with a designed-for-purpose amp that does match the low loop 
impedance.


Rudy N2WQ


There are a dozen ways to say the same thing, but the physical area of a 
loop (when it is very small) determines the maximum energy extracted. This 
is why small transmitting loops are all pretty much single turn and single 
conductor.


The sensitivity and what configuration produces maximum sensitivity has a 
great deal to do with the load placed on the loop and how the loop matches 
the load. For example, if the loop has a high impedance amplifier or 
matching system terminating the loop, it might be more sensitive with the 
extra turns in series rather than parallel.


Then we have things that are called loops and look like loops, but really 
function in a different mode than a small loop. All of the small 
unidirectional loops act like pairs of small verticals that are phased. This 
includes the EWE right through the flag or pennant. They ideally have 
uniform current, which is made uniform by the terminating resistance which 
terminates the wire in its surge impedance, but the vertical or sloped ends 
are what we want to act like the antenna.


It is pretty risky to generalize across everything, but what it all boils 
down to is the multiple wires can be used to improve the matching or reduce 
the losses. Which is more effective depends on the exact antenna and the 
things we have  terminating the antenna.


I wouldn't count on a system of more series turns, more parallel turns, or a 
thicker conductor, offering improved S/N or performance without know the 
specific system, the external noise, and the internal noise. Pretty much 
everything "loop" I have played with gets into propagated noise without 
multiple wires or a thick element.


The thickest element I have used was old flexible copper waveguide from a BD 
station, I think it was maybe four  to six inches and oval. I've also used 
ribbon cable in small loops, but as a series connected group. For all of my 
directional loops, I never used more than a single turn because they all 
occupied enough area to get into external noise.


If there was any magic in this, it would have been used 40 years ago. :)

73 Tom 


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Re: Topband: Using shielded CAT5 data cable as feedline for active antenna; benefits of multi-turn K9AY loop/SAL/etc?

[Tom W8JI]

2.  He cites experimental data showing that coplanar crossed loops and 
multi-turn quad loops both offer very significant improvement in the 
recovered signalcompared with a single loop.  See 
 to 
check whether I got this right. Anyway, it occurred to me to ask if anyone 
has ever tried multiturn K9AY, SAL or flag/pennant receiving antennas, and 
did you see something similar?


Be careful in what you might think the data means. The measurements are for 
an unmatched system, and apply to broadband untuned loops with "low 
impedance" loads.


In a case like that, the parallel wires reduce the impedance primarily by 
reducing reactance. It is no different than a thicker conductor, which would 
reduce reactance and increase current in the simple circuit.


This does not necessarily mean the loop would have a higher SNR, that would 
depend on how the amplifier "likes" the lower impedance and if external 
noise is limiting the system.


It does not mean more directivity. An even larger improvement in sensitivity 
would come from cancelling reactance.


If  a small terminated loop had increased conductor size it would have more 
sensitivity, which means increased signal and noise pickup, because the 
termination and source resistances would decrease.


You can see this effect by modeling an EWE antenna, or any small loop.  As 
the conductor is made thicker the optimum termination resistance decreases. 
This increases sensitivity, because radiation resistance remains the same 
and loss resistances decrease. You can pick up a few dB in sensitivity in 
certain cases.


If the amplifier or receive system is affecting S/N in a significant manner, 
it would improve S/N. If external noise is the significant factor in 
sensitivity, then it would pretty much do nothing.


This effect occurs in all sorts of lossy antennas. For example, if you 
paralleled two close-spaced Beverages (making them act like a single very 
wide conductor) sensitivity increases. This does not mean S/N ratio 
increases, because signal and noise from the antenna would increase at the 
same rate. It just means the level of signal and noise from the antenna is a 
bit higher.


If receive amplifier or system internal noise is helping set noise floor, 
then it would help S/N.


73 Tom 


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Re: Topband: vbog?

[Tom W8JI]

Has anyone tried a v-beam configuration on the ground, similar to a bog?
Obviously, it would be longer. The intent would be to increase RDF.

Or would that be a waste of time?



Waste of time to increase directivity.  Long wires laid on or near the 
ground fire straight down the length of a wire.


V-beams depend on the cone around the wires being overlaid and placed in 
phase at the center, so they depend on height and horizontal polarization. 
They require pretty good height to have worthwhile gain.


Many years ago (in the 70's) I had two reversible Beverages in a 90 degree 
V. I could fire them singly or in various phase combinations. I could skew 
directions or phase and null signals heard by both that way, get but it 
never really increased directivity. It just helped me null LORAN, or pick up 
signals better on a line bisecting the V formed by antennas. 


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Re: Topband: Commercial Antennas

[Tom W8JI]

My Ten Tec 238B L-Network tuner works well at 1500W. Some tuner networks, 
especially T-networks, can have very high currents through the shunt 
inductor.




The largest issue with T tuners is capacitor value. Most tuners use generic 
230-270 pF maximum capacitance caps, and that makes the network Q way too 
high on 160 into low Z loads.


The ATR30 has around 500 pF, and that makes quite a difference. It will 
handle well over 1500 watts on 160 without issues, and several kW on 80 into 
reasonable impedances. It has a lot of headroom for weird load impedances at 
1500W.


All that aside, I don't know why people would want to use a tuner to match a 
real low impedance anyway. Other than some tweaking to extend useable 
frequency range, the matching is really best handled at the antenna with the 
tuner just extending BW a bit. 


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Re: Topband: beverage resistors at Mouser.com

[Tom W8JI]

If you are going to make the order, consider using several in parallel to 
improve the surge handling capability.  I use 6x 2700 ohms here.


73/jeff/ac0c


Be real careful with the resistor choice.

A metal oxide or film resistor handles many times less surge than an OX or 
OY resistor. OX and OY resistors are 14kV and 20 kV pulse rated respectively 
without damage, and handle (OX) 40 and (OY) 70 watt-seconds for 100 pulses 
of 1 second at 50% duty.


A standard metal oxide is not remotely close, and paralleling 10 will not 
get them close. Even better MOX are only 10 watt-seconds, and not remotely 
close to the peak pulse voltage (which will not increase when they are 
parallel).


I've never actually had a single OY resistor used in a termination burn out 
from lightning, despite some pretty hard hits.  MOX are a different story 
entirely.


Either type works fine so far as reactance goes, unless the application is 
reactance critical. For a Beverage, reactance of either is not an issue. 


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Re: Topband: Beverage Crow's Foot Ground Wire Pattern

[Tom W8JI]

What is the recommended pattern for the crow’s foot ground wires at each 
end of a two-wire reversible Beverage?  Should ALL the ground wires be in 
the 180 degree plane behind the Beverage wire, or does it make any 
difference?  I don’t imagine it’s a very good idea to put a ground wire 
under, or very close to, the Beverage wire itself.

73, Art/W4AA
_


The antenna common mode impedance is 400-600 ohms.  What you do with a 
ground is not going to matter much, as long as the ground is less than 50 
ohms resistance or so.


Unless you are on permafrost, dry sand, or some other terrible soil just a 
couple ground rods are more than enough.  A few short radials are just extra 
insurance if the soil is questionable.




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Re: Topband: re topband QRP

[Tom W8JI]

I disagree. Since it is a category I find that some operators appreciate 
the information. It sometimes leads to a discussion about our setups.


With regards to miscopying someone. If you cannot intrepret the 
information sent because of a weak signal QRM or QRN you have not made a 
valid contact.




A person should never do that in a contest. Not ever.

It isn't actually even good to sign a "callsign/QRP" outside of a contest. 
It isn't a legal identifier, although it doesn't hurt anyone else as long as 
it is not a high rate or run contact series.


The real place for that in the non-contest exchange is during the ragchew. 
There is never a reason or place for it inside a contest exchange unless the 
contest makes it a mandatory part of an exchange.


I really hope people do not punish others by insisting on sending 
unnecessary, confusing, junk. That is what it would be doing, punishing 
others.


73 Tom 


_
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Re: Topband: QRPers calling CQ in the SP ?

[Tom W8JI]

Of course, any frequency ending in a zero is almost guaranteed to have a
constant broadcast station harmonic. I almost always hear them here,
especially at night. And very often, that BC carrier is stronger than
stations zero-beat with them calling CQ! Better to be slightly off of 
zero,

if you're QRP and want to be heard.


I could never understand that either. Anything USA on the 10's is likely to, 
sometime or another, have a mixing product or harmonic. 


_
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Re: Topband: re topband QRP

[Tom W8JI]

On Fri,12/25/2015 12:24 PM, mstang...@comcast.net wrote:
I operate QRP and normally give out that information as well as my power 
levels after the signal report.


As a QRP op myself, I urge you to NOT do that. If I had worked to dig a 
weak signal out of the noise, I would interpret ANYTHING after R or TU as 
telling me I had miscopied something, and you are repeating it.


NEVER send anything extra.


I agree 100% with Jim on this. The only thing sending /QRP or anything 
unnecessary does is make it take longer and make it more difficult.


I honestly think a good number of people will either just ignore a station 
signing nonsense or be confused by it.


There is nothing more frustrating than trying to dig out a callsign or 
complete a contact with unnecessary meaningless stuff tacked on.


73 Tom 


_
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Re: Topband: SB-1000

[Tom W8JI]

Thanks to all for info on the capacitor. The only place I had checked was 
rf parts but have not ordered yet. Also wanted to come up with a #8 brass 
washer. I'll go with a new original cap from Ameritron/mfj. I saw the 
plate choke there but not the cap, will follow the link. I'll still be on 
100W for a while. I've been hearing pretty well on beverage/Inv.L but not 
being heard that well on the Inv.L., Thanks again.

Jimk2hn
_


The OEM capacitor, which will be stable,  is $26.45   from Ameritron.

http://www.ameritron.com/Product.php?productid=290-0170-7

It is $29.95 from RF parts.

Both are N750 types. You need a #6 lug, a short #6 screw (3/16th long), and 
some #16 bus wire plus a brass washer that Ameritron will have.  The chokes 
come from Ameritron no matter where you buy them.


I'd just get it all from Ameritron, since they will also have the hardware 
and appear to be less expensive.


73 Tom 


_
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Re: Topband: SB-1000

[Tom W8JI]

If you can't find the exact value of 170pf  the ceramic 5KV door knobs at 
200pf will work.  Better yet even a couple of 500pf door knobs in series 
will give you 250 pf which will just mean a little less on your variable 
will tune.  Another common ceramic door knob value is 500pf and three in 
series will put you in the ball park.


NO.

170 pF was used because at 200 pF the capacitor breaks over into a different 
temperature coefficient. You will go from a N750 or so TC to up near or 
above N2000.


This will make the tuning drift with temperature.

Use the original part or parallel smaller values with the same or lower 
TC's. Also be ware the number on the case is often not met. Sometimes the 
caps cannot meet the stamped TC numbers. This is because the clay formula 
used is difficult to make temperture stable.


Just buy the correct part.

_
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Re: Topband: SB-1000

[Tom W8JI]

Both are N750 types. You need a #6 lug, a short #6 screw (3/16th long), 
and

some #16 bus wire plus a brass washer that Ameritron will have. The chokes
come from Ameritron no matter where you buy them.

Thanks Tom,Re. the lug, screw and wire, I'm assuming the capacitor I 
ordered from them will install with the lug, screw and wire that already 
exists? Didn't realize they had the washer also but will give them a call, 
possibly they can include it in the order. I did get the choke from them 
also. I also got one of F1BXL's parasitic suppressors he sells on Ebay. 
Hopefully all this will calm things down a little. The knowledge 
generously shared by folks like yourself, Jim and others on their web 
pages and this forum are greatly appreciated by all. Have a good Christmas 
and New Years to all.

Jimk2hn



I don't know who F1BXL is,  but parasitics have nothing to do with anything. 
I would not go sticking hairpins in there. That stuff is all heebie-jeebie 
voo doo.


The 160 tab is under the most stress when the amp operates 80 meters. There 
is almost 3kV peak across that 160 plate padding terminal to the switch 
rotor.  Every amplifier that switches a plate padding cap in has highest 
peak voltage on that tab when on 80 meters.


To reduce the electric field gradient around all the pointed areas of the 
contact, a washer is used. The washer acts just like one of those 
anti-corona rings that used to be in TV sets, or that you see on HV power 
lines. It spreads the field out, and reduces the chances of the corona 
setting off an arc when you are on 80 meters.


Voltage between the switch rotor and that contact is highly dependent on how 
you set the load control, because that sets the anode impedance. This is why 
people should **always** tune an amplifier up for maximum possible power at 
full drive and then back drive off to safe power. That reduces peak voltage.


I can, for example, make the anode of a 3-500Z reach 3 or more times the dc 
supply voltage if I underload the amp. As a matter of fact if it is severely 
underloaded, the voltage increases until something someplace absorbs the 
energy.  If it is a switch contact, then the contact goes away.


People can cast all the spells they want  with magical suppressors and, if 
the PA gets grossly underloaded for the peak drive power, something will 
arc.  That is just how these class AB amplifier systems work.


Ask Ameritron to include the parts. They do not normally come with the 
capacitor. When I released the SB1000 design to Heath, the release was real 
early in the run. I think we were at the first 100 or 200 AL80A's. That 
washer, plus a buck-boost winding to the transformer, came after Heath 
kitted the unit. What you have is a very early release of the AL80A, just 
after the AL80 was dropped. The AL80A was progressively refined until it 
couldn't be refined any more in that chassis. The next major revision was 
the AL80B, which had major changes. The AL80B remains pretty much unchanged.


73 Tom 


_
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Re: Topband: Heathkit SB-1000

[Tom W8JI]

Good point Tom, beginning with too little drive would require more load C 
than is available.  That and the brass washer should be installed also.




Hi Lou,

The anti-corona washer was not in the SB1000 or early AL80A. It should be 
added if a user might happen to mistune.


But I'd like to reiterate..the LAST thing to do is just start throwing 
padding capacitors in.  That tank will tune fine as designed unless it has a 
component or wiring problem, or unless the drive level is too low to match.


If it is being driven with 50 watts or more and does not tune into a 50 ohm 
load, I'd carefully inspect the entire tank circuit and wiring of the tank. 
This includes the switch (as Herb suggested).


Don't just go throwing parts in.

73 Tom


_
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Re: Topband: 160m LP to LP DX contacts in 2015

[Tom W8JI]

In order for us to respond to your allegations you will need to provide 
support evidence.  We will need details on his actual antenna 
configuration, was he using a counterpoise of some sort,  is he on a hill, 
how close is he to the water ?  Do you have proof that he was running more 
than 5 watts ?
Comparing his results to your test is meaningless, there are too many 
variables to consider.


While a list like this isn't the place for accusations, I'd like to offer 
some common sense on this because it goes broadly to the actual topic.


It is difficult to tell power level of people running poor antennas. A 
coaxial dipole actually has loss over a normal dipole and is no better for 
receiving, and we all know a low dipole is generally not good except special 
times.


A low dipole, however, can be surprisingly good at certain times. During 
band peak at sunrise or sunset, it can be competitive or above a tall very 
good vertical. The same is true during geomagnetic storms.


Back in the 60's, before everyone knew a lot about antennas, many stations 
used low power and dipoles and had impressive DX. But to be sure, it took 
months and years to work the DX. Very few people could run DX, it was doing 
good to work even a half dozen DX stations in hours of great effort.  For 
me, it was good to work one or two DX in an entire evening. It took many 
years, not just a contest weekend or two, to work DXCC on 160.


This was partly because of lack of stations, but mostly because people used 
poor antennas and low power. Even high power, prior to the early 1980's, was 
a kilowatt input or about 600 watts output. A California kilowatt was 
something like a 4-1000Awhich could really only make 1300 watts or so 
output normally in grounded grid, and 2 kW out if totally hammered.


If we look back at the TIME spent and the equipment and power levels, it all 
makes sense. No one ever had runs of 160 DX consistently even as late as the 
70's. It wasn't until 1500 watts and Beverages became normal that we were 
spoiled.


It is very easy to tell 5 watts from 500 because it is 20 dB, but it gets a 
little rough to tell 5 from 50. 10 dB (or even more) is easily in antenna 
and location differences even when close to the same area.


If a low dipole stands out from other similar or better antennas by a whole 
bunch, and it consistently better over a long period of time, it is not 
because it is a "special" dipole or "special" location. We know that because 
it is 1960's technology, and back in the 60's using that technology of low 
power and generally crappy antennas DX QSO's were rare and very difficult.


Antenna technology, noise, and QRM has made the spread in performance 
difference between locations much greater.


73 Tom 


_
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Re: Topband: SB-1000

[Tom W8JI]

Just came off 20M, amp working fine. Went to 160 plate and load controls 
have no control, no output. Plate current climbs high with any added drive 
(45-50W) and blew both 10amp fuses.Off comes the cover.jimk2hn

_


It might be something else, but  I would bet the contact on the 160 padding 
capacitor is burned off. This is what the anti-corona washer reduced. Heath 
did not use that washer.


It arcs there when the loading cap is too far closed (too much grid current) 
for the amount of drive on higher bands, or if the antenna should become 
grossly mismatched when at high power on bands other than 160.  The worse 
band for arcing the 160 padding contact is when on 80 meters.




_
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Re: Topband: SB-1000

[Tom W8JI]

Thanks to all. I will go over it again today. I initially started out on 
160 and then moved on to other bands. On 160 I could not get any increase 
in grid current, it came up but no increase with plate tuning but may not 
have applied enough drive. Staying below the 200ma grid and 400ma plate 
and just shooting for 500-600 watts on all bands right now. I did go over 
the switch before using the amp and it looked good and also deoxit it. The 
only thing I changed was 115v to 220. Probably just operator error since 
it's been a while doing any maxing and dipping:)Jimk2hn

_



A pi-L also tunes a little weird.

In a normal pi, the plate tune hardly moves with load changes. In a pi-L, 
the plate tune and load interact. But either has to be tuned near rated 
power.


Don't bother spraying a band switch that carries several amperes and 
thousands of volts. It never really does good, and it might do bad. Save the 
deoxit for volume controls and things that only have a few volts and a few 
mA current. 


_
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Re: Topband: Weatherproofing F-type connectors

[Tom W8JI]

Apply some silicone dielectric compound (non-hardening silicone "grease")
to the coax center conductor. That will keep moisture out and prevent
corrosion.



This actually belongs anyplace anything is threaded or clamped. It will 
displace from pressure and allow a connection, but it seal the joint from 
moisture and air.


I use it in connectors in my race car even. 


_
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Re: Topband: QRP

[Tom W8JI]

I have been puzzled with this question for a long time...
Given the progress on antenna and Rx-capabilities (over the years) and say
typical transceiver output power (100W),
how come it has become so rare to witness (experience) low power to low 
power

QSO's (over the USA to EU path)
during major topband contests (winter time on both continents) ?

What has happened to the topband conditions the last couple of decades?
IMO it is hard to believe this is due only to environmental noise 
increases?!




The largest problem is QRM. Mostly from intentional transmitters and also 
from hundreds of unintended transmitters that cause noise.


In the USA during contests, stations are stacked every few hundred Hz. 


_
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Re: Topband: 4SQ around tower

[Tom W8JI]

I am in the process of clearing land for full size 80m 4SQ. I have two 
questions for the group:


1) How much and what kind of degradation should I see if I place the 4SQ 
elements around my tower. The tower is 90' and has a 4 el 40 m yagi at 90' 
and 6 el tribander at 105'. Currently I have no plans to detune the tower, 
but do have plans to use it as a 160m TX antenna.


2) If the consensus is to move the 4SQ away from the tower, how far should 
I move it? Also, in what direction should I move it with respect to the W 
and S elements of the 4SQ.


What happens depends entirely on how the tower behaves on 160. It might 
cause great harm, or it might have no effect at all. There isn't a way to 
tell without either testing it or modeling it without EVERY metallic guy 
line and antenna accurately included in the model, along with ground points. 


_
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Re: Topband: 4SQ around tower

[Tom W8JI]

Thanks for the great reminder! The chapter does in fact describe exactly 
what I have been planning. It also gave me the most important piece of 
information- as long as the tower is grounded, which is the case, it has 
no impact on the 80m 4SQ.





If that is the actual statement, it is not a correct statement except in a 
very specific case.  If the tower is empty of any other antennas or guy 
lines and the tower is around 100-150 feet tall and grounded at the base, it 
would have the minimum effect on an 80M 4 square.


Every area of the tower and the guy lines and everything else around the 4 
square must not be resonant on the band the 4 square is on.



A couple of points:


1) The 4SQ is for 80, not 160. I am trying to decide if I should clear some 
forest to make room for it or just place around the tower. If it goes in 
the forest, radials become a nightmare


2) Currently the tower is just a tower, not a 160m TX antenna. If the 80m 
4SQ would suffer from gamma matching the tower than I have the option of 
building a dedicated 160m vertical in a new location. A lot of work, but 
less work than trying to lay radials in the forest.




Let me explain the issue a little better.

It doesn't matter one bit what anyone else does with a **different tower** 
on a different band or even on the same band. The center area of the 4square 
has very high field levels when the 4sq is active. The 4sq will couple into 
whatever is inside the 4 square, or around the 4sq on the outside.


If you just simply had a tower with insulated non-resonant guy wires, and if 
that tower was 120-140 feet tall and reasonably well grounded at the base, 
it would be almost perfectly non-resonant on 80M. It would have only a 
minimal effect on the 4 square.


The moment you add anything  to the tower that is metallic, the 
anti-resonant frequency will shift. How much anti-resonance shifts naturally 
depends on what is placed on the tower and where it is placed on the tower. 
This would even include feedlines that are not bonded to the tower, because 
they can act like parallel stubs. If they happen to shift the anti-resonance 
caused by the tower being about 1/2 wave long and grounded at the base, then 
you are in the soup. The first change will be a modification of F/B ratio, 
because the nulls are most sensitive to current ratios that will be upset by 
the presence of the tower. It does not take much re-radiation to hurt the 4 
square nulls. It takes more re-radiation to actually damage the gain.


A worse case example of this would be a tower 130 feet long grounded at the 
base. If I put a large 20M Yagi with grounded elements on the tower anywhere 
except down near ground level, the tower will no longer be anti-resonant on 
80. Moving the Yagi up and down the tower will change how the tower 
interacts, and there can be some very sour locations for the Yagi that would 
grossly affect the 4 square.


The thicker the tower is, the more difficult it is to make invisible. The 
more feedlines and antennas, the worse it is.


I have a 160 4 square surrounding a bare ~200 ft tall tower.  If I 
completely float that tower from ground, it just kills the performance of my 
4 square.  If I ground the tower, it knocks about 10-15 dB of F/B out of the 
4 square. I have to find a "sweet" value of reactance to put between the 
tower base and ground to make the 4 square behave.


If I put one Yagi on it, the Yagi mounting height and size would affect the 
impedance needed at the base to detune the tower. If I loaded that tower 
with Yagi's, I might never get it detuned. If I ran a feedline down the 
tower on the outside that was not bonded to the tower every 1/4 wave or 
closer on 160 (in my case where it is on 160), that might also cause an 
issue.


The case where we can carte blanche say there is minimal interaction would 
be when the tower is not too large a cross section, there are no metal guy 
lines attached, there is nothing else anywhere near resonance around, and 
the tower is about 1/2 wave tall and grounded at the base.


The mechanism that decouples the tower is the ground at the base plus the 
transmission line effect of the tower tries to create a very high impedance 
1/4 wave up, but that high impedance is "shorted" by the 1/4 wave section 
going up from the center to the open end. The top half tries to create a low 
impedance right where the bottom half tries to create a high impedance. 
This "detunes" the tower.


The thinner the tower, the better this works. Stick something else on the 
tower, and it all can change.


73 Tom


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Re: Topband: ON4KST low band chat

[Tom W8JI]

Thanks, but that doesn't fix the 40m clutter in the ON4KST lowband chat.
That's what I meant.

For me, adding 40m to the chat simply ruined it. I'd be willing to pay to
have it work like it used to, just 160 and 80.



40 meters is more like 20 meters than a low band.  From this part of the 
USA, 40 is open to Europe about 20 hours a day and hardly has QRN.


40 should not be rolled in with 80, let alone 160.


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Re: Topband: DX on 160, was: Topband QRP WAS

[Tom W8JI]

On 12/5/2015 5:43 PM, Mark Lunday wrote:
Bill, a question about your 160 meter antenna.  I have learned from the 
wise
old-timers on this message board that a vertical antenna with 
broad-banded

behavior is a lossy antenna.  Same with a vertical antenna that shows 1:1
match.


Some people might believe that myth, but it isn't true.

Bandwidth is a meaningless determinant of efficiency. SWR is meaningless 
also, by itself, in indicating efficiency.


Verticals with good efficiency have sufficient ground 
radials/counterpoise

and present approx 30 ohms impedance and therefore do not provide a 1:1
match (I think it's about 1.5:1 or something like that).  In addition, 
the
efficient verticals are not broad-banded.  Dipoles yes, verticals no. 
Also,

if your antenna is not a vertical on 160, then as you know it will be an
even bigger challenge to work DX on TopBand.


A 1/4 wave tall tower with a perfect ground system will cover all of the 
band with reasonable SWR change. If series fed they will be around 30 ohms 
depending in many things, but that still does not tell us efficiency.


efficient verticals are not broad-banded.  Dipoles yes, verticals no. 
Also,

if your antenna is not a vertical on 160, then as you know it will be an
even bigger challenge to work DX on TopBand.


Actually that is exactly backwards, Mark.

Dipoles are narrower than 1/4 wave verticals, all things equal. This is 
because a 1/4 wave vertical has half the resonant length.


73 Tom 


_
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Re: Topband: 2 wl loop, worth the effort?

[Tom W8JI]

You are misinterpreting the model data by looking at the shape of the 
pattern rather than the relative strength of the pattern at angles of 
interest. Example -- the so-called "take off angle" simply shows the 
vertical angle where the signal is the strongest. FAR more important to 
look at the field strength at various angles as the height is varied.


Many people talk about and look at TOA, and it causes them to pick antennas 
that are actually worse just because the TOA is at the correct angle. :)


If you look at a low dipole, it has just about the same gain as a low loop. 
Being a loop helps moderate impedance on harmonics, but not much else.


I have 300 ft of height here. For the most part, a vertical did as well or 
better than a dipole at any height and distance. The exceptions were at 
sunrise or in magnetic storms, or within 50-200 miles (where a dipole below 
150 feet works much better).  Compared to a vertical, there could be 10-30 
dB difference in favor of a low dipole (less than 150 ft high) within a few 
hundred miles. 


_
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Re: Topband: 2 wl loop, worth the effort?

[Tom W8JI]

You said "Compared to a vertical, there could be 10-30 dB difference in
favor of a low dipole (less than 150 ft high) within a few hundred 
miles.",

and I was pretty much trying to make the same point but indirectly since I
don't have a dipole on 160 meters.

The original poster mentioned relatively short distance work on 160 
meters,

and that is why I mentioned that a true vertical may not actually be his
best choice (he might actually go backwards in performance if he is trying
to work stations in adjacent states as an example).


I've done hundreds or thousands of tests. I was test crazy when I moved 
here.


Within around 100-200 miles, at night, the verticals and a dipole up about 
1/2 wave are really dead compared to a "low" dipole.


That problem rapidly vanishes with increased distance, and during daytime 
skip zone of the high dipole moves in closer.  From my house the skip zone 
of a 280 ft high dipole is about 10-50 miles. The  vertical never really has 
a skip zone in the daytime. Groundwave fills it in.


I initially thought a low dipole (or a high dipole) was worth it, but I 
outgrew that. I just live with the weaker signal in the skip zone. The 
vertical does so much better at most distances most of the time it is just 
not worth worrying about.


If I wanted to work 50-200 miles, I'd probably just use a low dipole. 


_
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Re: Topband: 1/2 wl verticals and spaving

[Tom W8JI]

I'm glad to hear that it's that simple.  I used the same principle when the 
verticals were dedicated to 40M and were 1/4wl tall where I fed them with 
3/4wl and 5/4wl coaxial runs.  The gain and side nulls were impressive.>>>


Carl,

This is real simple to handle.

With a 1/4 wave or odd 1/4 feed to a current-fed vertical, the feedline 
needs equal voltages at the phasing unit to force equal currents. If it was 
a 1/2 wave feeder, it would require equal currents.


With a voltage fed antenna and a 1/4 wave feeder to the phasing unit, it 
would require equal currents at the phasing unit. If you make the feeder to 
each vertical 1/2 wave long, then it takes equal voltages at the phasing 
unit just like a normal current fed does with 1/4 wave feeder.


The issue with this is transmission line properties in the matching system 
at the vertical can upset what you think is the transmission line length.


With the 1/2 wave wide spacing you really only have the choice of in or out 
of phase for any pattern with deep nulls, so none of this really matters. 
Each element would have the same impedance.  If you had a unidirectional 
pattern it would matter.  I probably would just run a catenary line between 
the towers and drop a pair of wire elements for 40. If the verticals would 
support that, then you could get a unidirectional end fire pattern with 40M 
elements.


At 1/2 wave spacing, you are kind of stuck with limited patterns with very 
modest gain and no unidirectional pattern. 


_
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Re: Topband: Diversity-capable transceivers

[Tom W8JI]

Barry,

It is more than just second receiver quality. For maximum diversity effect, 
the receivers must use a common time base for both channels. They do not 
have to be phase synced (unless blended into mono), a person's brain will 
learn around that. The channels should not drift phase when on a given 
frequency, and if phase changes with tuning, it should be very gradual.


This can be checked by running a common oscillator or carrier signal into 
both channels and listening in mono. Another test is observing background 
noise with a single antenna common to both channels. Listening in mono can 
be as simple as laying the headphones on the desk. There should be no beat 
warble or no fading and peaking on a carrier, and when the band is swept on 
noise any change in apparent audio level with frequency change should be 
very gradual.  Ideally there should be no changes at all.


My R4C's, because I used one receiver's oscillators to run both channels, 
were perfect. The K3's I have are imperfect, they have a gradual phase 
change between channels with frequency.


My FT1000D was terrible, as was the Orion I had. They gave some diversity 
effect, but were so far unsynced they did not give the deep noise digging 
the K3 or R4C system would.


If you never use a system that is phase locked, you might not realize the 
difference. The channel audio phase relationship has to be stable without 
drift to get the real enhancement. 


_
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Re: Topband: fixing beverage

[Tom W8JI]

I've been doing FFT-based measurements since 1982.  I suggest that you try 
a technique before you criticize it. Your analysis is badly mistaken.


Jim,

Factually, the little bumps or even big bumps on VHF are meaningless for 
active problems on lower frequencies.   They might predict a future issue, 
but on 160 meters even crushing a cable flat for five feet would be 
meaningless for receive loss unless the center actually contacted the 
shield.


This is just the way things work, and it is important we get our heads 
around the way things work.


If I wanted to find the reason for high signal loss on 160, the last thing I 
would ever do is look at the system on 150 MHz or even 30 MHz.   I would 
first look at the system down around where the problem is, or as close as I 
could to that frequency.


I can go out and slice half of the shield off for 10 feet and not tell a 
difference in receive 160 signal, but it would be terrible on VHF. VHF 
certainly tells us a future problem or a defect nicely, but it will not 
directly point reliably to the LF issue unless by chance there is only one 
bad spot.


I use a TDR when applicable, and that is about once every three or four 
years. I can find and fix any cable system for HF with a cheap common SWR 
analyzer, and so can anyone else. I can sit in my house and find a bad 
connection 1000 feet away by sweeping the SWR between 1.8 and 5 MHz, and get 
within a foot, and not spend $500 on equipment.


73 Tom 


_
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Re: Topband: fixing beverage

[Tom W8JI]

There are multiple ways to do TDR. I like the way that this unit does 
it -- an inverse FFT of a frequency sweep.


http://sdr-kits.net/VNWA3_Description.html

To expose small perturbations in the feedline or system, make the sweep at 
VHF/UHF. To see only the more gross defects, sweep from about 50-150 MHz. 
To understand this, remember that a linear frequency sweep will spend more 
time in the high octaves than the low ones, so the greatest contribution 
to the display will be that higher octave, whatever you have chosen.


Actually, to see the more gross defects, we would look at a lower frequency. 
I don't want to imagine what my 160 stuff would look like at VHF.   :)


A system can have a  500 ohm transmission impedance bump 1 foot long on 160 
meters and it just doesn't matter. The general rule is if a reasonable 
impedance discontinuity is less than one degree long, it will not upset the 
system. SO 239's, for example, are about 35 ohms in the female's joining 
spring part (the males are nearly perfect). The effect of that bump is 
nearly immeasurable below 100 MHz.


We all know a one foot long chunk of wire that might be 400-800 ohms surge 
impedance barely changes SWR and adds immeasureable loss between the coax 
and a vertical base on 160. Same reason. Although the wire is a "major" 
impedance bump, it is electrically not too long.


What we cannot tolerate on 160 are resistive series connections and low 
resistance shorts shunting the system, or cross coupling from sharing common 
currents.


On 160 meters, if we simply measure RF voltage across the input of a line 
while sweeping low frequency, recording the repeating frequency of voltage 
minimums, we can find the distance to any cable or connection problem 
affecting the system by more than a few dB. Little lumps and bumps at VHF 
might locate a future issue like a chewed shield, but for an existing signal 
loss they are just a distraction.


If a shield develops high resistance 800 feet from my house, the high series 
resistance will cause a repeating voltage null 800/492 = 1.626 MHz apart.


If I swept the line and saw repeating nulls spaced 3 MHz apart, I would know 
an issue existed 492 / 3=164 electrical feet away.  If the cable was .85 vf 
, the issue would be 164*.85 = 139.4 feet away physically. This would be 
true for an open or a short.


All the software and refinement does for locating major existing issues 
affecting level is eliminate the use of a calculator. Any SWR measuring 
device, or even a simple voltage indicator, could do the job.   I can find a 
bump affecting receive levels with a Heathkit VF1 VFO and a 1N34 diode and 
meter about as well as I can with a TDR on 160.:) 


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Re: Topband: fixing beverage

[Tom W8JI]

Any antenna analyzer with variable frequency can be used as a TDR of sorts. 
Anything will work.


The method is very simple. You simply observe how far apart in frequency the 
repeating gyrations in impedance are, and use standard 1/2 wave formulas to 
convert the difference frequency to distance.


I can do this with a low power VFO and a diode detector or scope.  It does 
not even have to be a bridge.  :)


73 Tom 


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Re: Topband: fixing beverage

[Tom W8JI]

I notice that my USA beverage is lower in 3-4 S units that some weeks ago.



5-20 dB. Depending on receiver and where it is at on the S meter.

That has to be a poor connection, open, or short between the receiver and 
the Beverage transformer end of the Beverage. It cannot be at the 
termination end.




At simple view all seems to be OK. I think the coax is not the problem,
because if I have a problem in the coax, will be completely deaf, right?


No. Coax can do this. It happens all the time. Especially at connectors.



So this can be the cause of a problem in the end resistor or maybe in the
transformer?  I use in this beverage a WX0B beverage boxes



It can not be at the end resistor termination.

The problem is if you disturb something it will often start working. You 
need to carefully check one thing at a time. Many times, if not most times, 
this is corrosion or tarnish on the center pin of the coax. Sometimes it is 
a broken wire, or a bad part from lightning or water.


The best way to test it is with an SWR meter and do a frequency sweep from 
the house, before you touch the antenna or any outside connections. The 
frequency of either adjacent major dips in SWR or impedance will allow you 
to calculate exactly where the problem is. The MFJ analyzer will do this 
within a few feet, even on a 1000 foot cable, by using distance to fault.


73 Tom 


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Re: Topband: Mag loop 400W if possible.

[Tom W8JI]

Loss is I squared R. as the current is lowered then loss drops rapidly.


That isn't true.

Loss as a percentage or as a ratio to applied power is exactly the same in a 
linear system. 6 dB loss is 6 dB loss whether at 1 milliwatt or 1 megawatt. 


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Re: Topband: Mag loop 400W if possible.

[Tom W8JI]

The question always is the amount of area inside the loop and keeping the 
most distance between opposing sides. There are no tricks or magic. It is 
all about low resistance and maximum physical size. More loss will help it 
handle more power for a given capacitor voltage, but you don't want that.


All of the tricks like helical winding or multi turns to make a loop "work 
better" never actually help, and actually hurt. That's why all the 
commercial loops settle on a single largest possible conductor and largest 
size design.


The biggest electrical issues will be connection resistances and how well 
current and voltages are balanced in the loop, especially in relationship to 
the feedline and any mast.


73 Tom



- Original Message - 
From: "jonathan white" 

To: 
Sent: Sunday, November 15, 2015 7:59 AM
Subject: Topband: Mag loop 400W if possible.


Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can 
anyone give me details of a mag loop that will fit in a room and also be 
able to be taken apart and resembled on a beach,will use big vac cap 
1000pf 40kv Russian type,any takers,and please dont laugh I love topband.

73`s Jon g8ccl
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Re: Topband: RX PREAMPS

[Tom W8JI]

I  have used the HI Z rx system and also the DXE ones.  HI Z said in the 
past no need for a sequencer to get power off the amps if the xmit ant was 
close to the rx system antennas.  Close I would say 60 foot.  DXE has 
always suggested using a sequencer to get power off the amps during xmit. 
I am going to be forced to move a DXE system within 65 ft or so of my 160 
vertical and wonder if anyone has had any experience of using the DXE 
without a sequencer close to their xmit antenna.  Just hate to install one 
more thing I could get around but will if absolutely necessary.  I know 
moving it closer is not an ideal situation but you do what you have to. 
Any input?  73 Mike K4PI

_



You actually have to try it and see. Interaction depends on the very fine 
details of the system, including cable lengths and the transmitter system 
does to the feedline when on RX and how the RX antenna couples to the TX 
antenna. As such, there will never be one universally true answer, so asking 
others won't really tell you how it will work with your system.


I do know that what Hardy said is basically correct. It models that way, it 
works the way he described.


If I place any RX vertically polarized antenna around my 160 TX antenna, 
even if the RX antenna is 250 feet or further away, I can always see a 
substantial interaction with certain termination changes in the TX antenna 
array when receiving. The only exception is if the RX antenna design nulls 
coupling to the TX antenna.


An RX antenna cannot be designed to be immune at such close spacings, unless 
it places a pretty deep null in the direction or in the polarization of the 
TX antenna.


So you have multiple things affecting how it will work:

1.) How your system terminates your TX antenna when on RX

2.) If the RX antenna nulls the TX antenna, either by pattern and/or by 
polarization


3.) What level damages things or affects things

4.) What else is around

5.) What people call good enough

and so on.

Since no two systems are identical in every single way, you just really have 
to try it.


73 Tom 


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Re: Topband: Mag loop 400W if possible.

[Tom W8JI]

His 400W TX power will likely be ~10 watts ERP if he does a good job on 
construction.   390W will be nothing but heat.


:)


- Original Message - 
From: "Barry N1EU" 

To: "topBand List" 
Sent: Sunday, November 15, 2015 8:59 AM
Subject: Re: Topband: Mag loop 400W if possible.



Wish you all the best with the antenna project Jon but not sure your
apartment neighbors are going to love your indoor 400W on topband  ;-)

73, Barry N1EU

On Sun, Nov 15, 2015 at 12:59 PM, jonathan white <
jonathan.whit...@btinternet.com> wrote:


Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can
anyone give me details of a mag loop that will fit in a room and also be
able to be taken apart and resembled on a beach,will use big vac cap 
1000pf

40kv Russian type,any takers,and please dont laugh I love topband.
73`s Jon g8ccl
_
Topband Reflector Archives - http://www.contesting.com/_topband


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Re: Topband: Why do rodents eat coax?

[Tom W8JI]

Squirrels and rats can be a problem, but mostly my cable chew issues have 
been from raccoons. I used to trap them and deport them a few miles.


Now I just I bury my cables. Even a few inches of dirt is enough. Where they 
come up out of ground, I sleeve them with cheap plastic sprinkler pipe.


You can splice out the bad areas, but you have to bury, sleeve, or fix 
whatever is eating it.



- Original Message - 
From: "Dave Olean" 

To: 
Sent: Monday, November 09, 2015 2:38 PM
Subject: Topband: Why do rodents eat coax?


I was transmitting on 160 last week, and after calling a CQ I noted that 
the background noise from one of my beverages dropped to almost nothing. 
Something obviously broke right then. All checks pointed to something 
external to the shack. I finally got out in the woods and checked the 
antenna system. All looked great. I used my new SARK-110 vector network 
analyzer and saw very believable results when connected to my 1100 ft long 
Europe beverage: about 75 ohms impedance and a VSWR that fluctuated between 
1.5 and maybe 1.8:1 across the freq range. I double checked the entire 
beverage run for shorts or anomalies, and even took apart the termination 
box to make sure all was OK. The last thing left was the 1000 ft run of 
flooded RG-6 coax. I had run the cable on the ground back to the house 
about 2 years ago. It was mostly invisible now, being covered with leaves 
and moss etc etc. A TDR check showed gross "bad" things and a VOM test 
across the center pin to ground showed a resista
nce of 35 ohms while the far end was terminated in a 75 ohm load. 
Obviously the cable was compromised. I made a quick inspection and found a 
few spots where small animals had chewed on the coax enough to break 
through the outer plastic covering and into the braid and aluminum foil 
shield. Water and gunk have caused a low resistance between center pin and 
the shield.
   What are my options now? I don't want to spend another $150 for another 
roll of coax just so a squirrel can feast on the PVC. Should I route the 
coax in the air and away from small mouths? That is one option.  It seems 
that digging a 1000 ft trench thru the woods and burying it would work, 
but it would be an awful big chore for a 70 year old doofus. I doubt that 
I could manage that. If I run the coax above ground, I run the risk of 
picking up noise etc. I also worry about falling limbs and old dead trees 
falling on it. With a few beverages in the woods, I can't afford to spend 
$150 each time an animal feasts on it. I need to do something different!
   Incidentally, the beverage still has great directivity, but signals are 
very weak with the bad cable. It is barely useable now as a result.

73
Dave K1WHS

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Re: Topband: Fwd: BCB Interference

[Tom W8JI]

The first thing I would do is find out if it really is AM BCB stuff, or SW 
BC, or what it actually is.


BCB filters won't help if it is a 3 MHz SWBC, or something just above 80 
meters. Filters also will not help if it is rectification in the antenna 
system, or a real signal from mixing or a parasitic somewhere else.


I've  had broad spectrum noise like that from AM transmitter issues, some 
from Georgia and some from other states, and some SWBC station WWCR.


I had one AM station in Georgia licensed to run just a few watts at night 
that was running a kilowatt, and the transmitter also had a wide parasitic 
that went from 1600 kHz up past 3 MHz. I had to drive halfway to Savannah to 
locate it.


One thing happening now is AM stations share antennas, and SWBC stations 
nest antennas close together.


Generally what I do is listen to the distorted QRM audio on one ear,  and 
start at the low end of the AM BC and work my way up through shortwave 
looking for a signal match. Almost all of the time I find the match, and 
some of the time it isn't even stuff from the AM band.


Usually, but not always, mixing is on spot frequencies. Usually, but not 
always, real wide stuff is arcing or parasitics at the BC station.


Almost always a 10-30 dB filter cleans up a receiver. If the transmitter 
were right next door, you might need 50-60 dB. If you are sharing a feedline 
with them, then you need in the 100 dB range of filter. One port mixers with 
signals all through the same port are not linear with padding. If you can't 
hear a significant change with 10-20dB attenuation, the mixing is probably 
not receiver side of the attenuation.


Before throwing too many bypasses or filters at things, I'd try to get some 
idea what it is.


73 Tom 


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Re: Topband: 160m & 80m RFI issues requesting ideas for ANC4 senseantenna to cancell out local noise

[Tom W8JI]

Does the SNR of the targeted noise source vs. other signals on the sense
antenna, matter in this application?




To null a particular noise, you want the noise antenna to have the highest 
unwanted noise pick up possible and the least amount of signal or other 
background noises.


If the noise antenna has other noise or signals, it will add them in to the 
mix. 


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Re: Topband: 160m & 80m RFI issues requesting ideas for ANC4 senseantenna to cancell out local noise

[Tom W8JI]

I have an intermittent RFI issue that comes from a subdivision about a 1/4 
mile away.   To combat the noise I have been trying to use my ANC4 and I 
built a sense antenna out of an 80m hamstick that I put 20 feet in the air 
yesterday for a trial to cancel the noise on 80m (cheap and easy 
experiment).   The location of the sense antenna is at the corner of my 
lot as close to the subdivision that I can get.  The design is the 
hamstick as a vertical element and two 102 inch whips as elevated radials.




102 inch whips would not be an effective counterpoise unless one or both:

1.) The whips were loaded to resonance with a high Q coil, at which point it 
would be a single frequency counterpoise and still require a good feedline 
choke


2.) The feedline had a much high common mode impedance than the common point 
impedance of the whips


Without the above, the coax shield is mostly the antenna...not the Hamstick. 
You would have been much better off with a ground rod.



The noise is s9 on my 1/4 wave 80m vertical and 160m inverted L.  This is 
a multi band vertical with wires for 40m, 80m & 160m.   I also have other 
antennas such as a 160m 2wl long loop and a trapped dipole.  What is 
interesting is that the noise is significantly less on the loop and the 
dipole.   I attribute this to the noise being vertically polarized based 
on my research on the internet.  Also this sense antenna is roughly 150ft 
away from the vertical antenna.




That actual reason for that is the earth acts like a short circuit and 
attenuates any horizontally polarized ground wave.


The low horizontal antennas also have very poor ground wave response.

This combines to make horizontally polarized antennas less sensitive to 
distant ground wave noise.


The issue is the level of the sense antenna noise is significantly less 
than the vertical and I am not able to find a null point that makes a 
difference.   I can however use the loop antenna and I have enough signal 
with the hamstick experiment to get a null as the received level of noise 
on the loop is significantly less.  So I believe I need more receive gain 
on the sense antenna.


So with the above in mind, is there a low cost pre-amp that I could use on 
the sense antenna to boost the signal?   Or what other ideas are there for 
a sense antenna.   I don’t want to put up another 1/4 wave antenna for 
sensing.   I have read where folks suggest putting 50 ft leg dipole at 5 
ft above the ground for 80m & 40m but I think the noise is vertically 
polarized and this wont do much but I could be wrong and have been wrong 
before.




I would build a ground mounted vertical sense antenna with amplifier,  use a 
ground rod as a ground, and decouple the coax near the sense antenna. A 
simple J310 source follower  amplifier on a 102 inch whip would have a ton 
of signal level.


73 Tom 


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Re: Topband: RFI - and lots of it (negative fuse)

[Tom W8JI]

My Icom radios come with the power cord fused for both negative and
positive.  From what you say, I should remove the negative fuse if I 
install

the radios in a vehicle.  Now when the radios are at the fixed station the
same power cord is used (both lines fused), I understand that the negative
line fuse should also be removed.



The standard from UK is well worded:

"4.6.4. Negative Feed Connection
In the case of negative earth return vehicles, the negative power line 
should not be fused. It should be connected to the vehicle body as close as 
practical to the point at which the battery-to-body connection is made. Do 
not connect the negative power line directly to the battery.
For heavy commercial vehicles (>7.5Tonne GVW) only, and those vehicles with 
tilting cabs where the cab may be isolated from the chassis by rubber 
mountings, a ground point is provided by the vehicle manufacturer within the 
cab to provide battery to cab grounding. Generally this is located within 
the main fuse box. It is recommended that this point be used for 
installations in this instance.  With certain equipment it may be necessary 
to connect the negative supply line to a local earth point. In this case an 
existing vehicle earth point must be used."


I just went through terrible problems with an aftermarket EFI system that 
insisted on a battery negative connection. It never worked properly until I 
used the vehicle chassis as the negative.


I regret now, after years of experience with problems, ever following the US 
and Japanese standard of using a battery negative pole or terminal, and not 
the vehicle chassis.  I still, because the warnings to use the battery 
negative were so strong in an expensive EFI system, I followed it (knowing 
better) and had a ground loop noise problem right away.


I've damaged radios and accessory equipment several times over the years, 
and the ground loop also makes common mode noise and audio hum and noise 
problems worse. I used to buy into the common advice, because I never really 
thought about it. No negative fuse holder for me, and no negative battery 
post connections for me. My three wire plug shack power supplies have all 
been modified now, and no longer have a ground loop from mains or station 
ground to the negative power lead.


The UK standards have it correct.

73 Tom 


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Re: Topband: RFI - and lots of it

[Tom W8JI]

Way back in the '90s, when I served on the SAE automotive RF immunity and
emissions (EMI & EMR) committees, questions about why we have 
negative-lead

fuses in ham radio gear came up from time to time.  (Many of us on the
committees were hams.)  The reason we were given is that there was a
scenario in which the negative battery lead ground failed, and the radio
negative became the best path to ground for the starter motor, 
particularly

if the radio negative was screwed to the negative battery post.  In
retrospect, this seems far-fetched, but the OEMs don't like to hear 
stories
about electrical fires in their vehicles, so somehow, this was 
communicated

to the radio manufacturers, and negative-lead fuses became the rule.



Any good connection to the chassis anywhere on a unibody vehicle is far 
better than a connection to a battery negative. Motorola is smart enough to 
tell installers to ground to the chassis, not the battery. In the UK the 
directive is to use the chassis or a manufacturer supplied terminal, and it 
specifically prohibits connecting to the battery negative pole.


The negative fuse is just foolishness. If it opens, all the radio current 
goes through small wiring. If the fuse opens, there goes the radio or 
something connected to the radio via a port. All of the radio current will 
go through some small wire.


My shop bench radio has an open foil on the CW key line and the mic because 
of a fuse holder failure, and that isn't the first radio that has that 
happen.   :)


The entire problem centers around use of the battery pole or battery 
connector as a source, and this carries over into our station desks. There 
is a ground loop similar to that in a car created between the power line 
ground, the power supply case, the negative lead, and the radio chassis back 
to ground. As in the car, if this stuff was built or wired correctly, the 
12V bus would only be grounded at one point and there would be no negative 
fuse.


In our houses, many of the problems blamed on RF feedback are actually 
ground loops caused by grounded cabinets common to negatives and voltage 
drops on negative leads.


At least some places in Europe got their together and banned battery 
negative connections because of the hazards.


73 Tom 


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Re: Topband: RFI - and lots of it

[Tom W8JI]

Yes, or where other premises grounds are tied together. Systems like 
Telco, CATV, satellite, even lightning rods if there are any, building 
steel if there is any.




It doesn't matter where in the world we live, electrons all follow the same 
physical laws.

There are three things that should apply to advice:

1.) What really works and actually is a good thing to do
2.) What is a bad thing to do
3.) What still meets but safely works around local codes

The USA and Japan does some really stupid things with 12V radio systems, 
like negative lead fuses and power sources and radios with negative 12V 
rails tied to ground at both ends.


The UK is smarter on that, with requirements a mobile negative NEVER go to a 
battery negative post and never have a fuse. This should, through common 
sense, apply to a 12V supply on a desk 12V powered Ham radio. We are, 
however, locked in a loop of doing things the wrong way because that is how 
we do it.


The USA is good with the use of a common entrance point ground for 
everything, where all utilities like CATV, Telco, safety, and power have one 
single common "entrance" ground point, although that is sometimes missed. 
The ground rod means very little compared to the importance of the common 
bonding.


Our local fire station caught fire from a lighting strike because the fools 
they hired to do a wireless internet system just run cables in willy-nilly 
through plastic pipe because it "meets code". Occasionally they will have 
problems at different county buildings in storms because they have utter 
nonsense in the wiring, but it "meets code".  So far they have had a fire in 
a fire station (and destroyed much of the computer gear), lost the tag 
office, and lost things at the sheriff's dispatch system.


But the system that will keep burning up, and maybe eventually even kill 
someone, does meet code.  That is what matters.   :)


There is little that can ever be bad about using a single point ground, but 
adding a second path to ground (which no longer makes it single point) can 
quickly become a disaster.


It doesn't matter if we are in London or LA, electrons and grounds work the 
same way. The issue we face is making sure it works correctly, while not 
violating codes. Meeting codes is NOT a cure, and can cause a problem.


73 Tom 


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Re: Topband: RFI - and lots of it

[Tom W8JI]

I have and electrician coming next week who says he will check things out 
and first of all ground the breaker panel to two ground rods 7 feet apart. 
I thought the grounding was put at the meter but he says they don't do that 
anymore. I think the old meter, before we had the new one put in had a 
ground rod beneath it but nothing now. The only ground I could find to the 
panel is a skimpy wire going to a water line. All of which looks corroded 
etc.. I know many dollars were spent on renovation and restoration of this 
place but I'm afraid to much emphasis was placed on cosmetic and not enough 
on electrical as I look more closely, pretty depressing. >


Jim,

Just keep in mind when  you do the work, the quality of the house ground to 
earth is far less important than having everything entering the house being 
bonded to act like one common point.


One of the biggest mistakes in amateur radio grounding over the decades has 
been having the shack antenna and control cable entrance ground 
non-existent, and the common shack desk equipment ground to an independent 
ground.


The shack ground must be bonded to the mains ground so everything entering 
the house is as close to one potential as you can get it.


Correcting things may not cure your RFI, but it always makes things much 
safer and more reliable.


73 Tom 


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Re: Topband: interconnecting cables

[Tom W8JI]

I am curious about terminating RG-6 cable connections in the ham shack.

I have been using several types of adapters, i.e. F female to BNC male,  F
female to UHF male, or F female to RCA.



I use F's up to the actual radio stuff, then I am forced to use what the 
radios use. I have a lot less luck with BNC than I do phono connectors. 
BNC's are often a lousy ground connection over time. Unfortunately, radios 
require what the manufacturer uses.


In order of shield reliability over time in common small connectors, I've 
found it is N, UHF, F, phono, and BNC.  For lightning, it is UHF, N, F, 
phono, and BNC. My security system uses BNC and phono, and it is a constant 
issue for having to clean and reseat the BNC connectors. Same with my radio 
gear.


I never have to reseat a UHF,  N, or F.  Very rarely a phono connector 
issue, but they are only indoors. The BNC are a pita, inside or outside.


73 Tom 


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Re: Topband: RFI - and lots of it

[Tom W8JI]

I have driven copper ground rods in about ten years ago, then wrapped a 
couple turns of #4 wire around the top and soldered that to the rod using 
plumbers solder. These connections are as good today as the day I soldered 
them. Plumbers solder works very well outdoors for me. I use it on 
everything outdoors now.


Dave, W5UN


80 year old broadcast radial systems are still good with silver solder 
connections. My 318ft tower gets whacked all the time and has silver 
soldered connections. They never melt. Even RF radials that augment the 
lightning ground, which are plumbers solder #16, do not get hurt.


The main reason NEC and other codes don't like solder is they don't trust 
people to know how to solder.


Of course the heat is I^2 R  times the time. It isn't just current, it is 
joules.  If the solder connection is good with low resistance, it will not 
get hot.


Also, there is no possible way a rod system could stay anywhere near zero 
volts in a strike. Almost all of the protection to equipment and the house 
itself is by the common point connection of things entering the house 
outside the house.


We certainly need the rods, but most of the protection comes from bonding of 
all things entering the dwelling. Very little of the protection inside the 
dwelling actually comes from the rods.


With a tower or tall structure likely to be hit, the structure ground can be 
a major player. That ground keeps strikes from raising the base voltage so 
much, and reduces common mode into the house grounds. It takes a pretty big 
ground system to not elevate in voltage in hits. A couple rods will not do 
it, even if they ohm just a few ohms at low frequencies.


73 Tom 


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Re: Topband: RFI - and lots of it

[Tom W8JI]

Everything you do properly to reduce the chance of common mode noise being 
conducted into the house will also reduce RF feedback, power line fault 
damage, and lightning damage risks.


Even if it makes no difference in noise, it pays back in increased safety.

This house had expensive lightning protectors on the power line at the 
service head, but the only ground was a cast iron pipe with a loose rusty 
steel clamp. I threw the surge supressors away when I upgraded things over 
15 years ago. Despite adding towers that get hit quite often (a few times a 
month in thunderstorm seasons), I never lose anything. Not even a modem.


The only common damages are meleted cables and wires outside the buildings, 
but nothing can prevent that. 


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Re: Topband: Re. RFI - lots of it

[Tom W8JI]

I forgot I had this up with pictures.

http://www.w8ji.com/power_line_noise.htm
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Re: Topband: Re. RFI - lots of it

[Tom W8JI]

Rain on the way so will know for sure what conditions are best. Hopefully 
not the same as Tim or Kriss since this is big Lake effect snow country 
although you'd think snow would melt at an arcing area. We are expecting 
60mph winds tomorrow and rain. Regardless, power company is sending 
someone "to take a look". Noise is still down but not gone since the wet 
weather stopped.jim/k2hn

_


Wet weather noise is often corona related, but sometimes defective 
insulators, cracked, scored, or dirty. I had problems with 345kV line corona 
in Ohio when the weather was damp.


Dry weather noise is often slack spans allowing the metal pin joints or ball 
and socket joints in insulators to arc from capacitive coupling. The metal 
on metal corrodes and makes a tiny layer of oxide that arcs from capacitive 
coupling and leakage.  Hitting a pole with a hammer finds that, because it 
shakes the wires and wiggles the metal joints.



There are so many different things that can cause noise, however, that any 
Internet diagnosis is mostly a wild guess.


The best thing to do before doing anything is try to track it with a VHF AM 
radio, like a portable aircraft radio. I have commercial noise locating 
equipment, but the last time I lent it out it came back broken.  :(


73 Tom 


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Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: ADC Overload from MW transmitters

[Tom W8JI]

I think the problem here is some people read this as a SDR radios never 
overload, or are superior in every case.


Apparently one person thought they were junk because multiple modest 
strength signals would add up to overload them, and that triggered the 
response that was misinterpreted to mean they never overload under any 
condition or were always superior to roofing filtered systems common in 
standard receivers.


In the case I had here, a *single* transmitter totally wiped the SDR out. 
The overload was nothing like the desense or noise in a traditional 
receiver. It just was totally useless. It was useless at any signal spacing, 
because it had no front end selectivity at all that would reduce levels.


For my application, it was useless. It was far worse than a K3, which a few 
kHz spacing would duplex on most antenna combinations. When the K3 (or 
FT1000MP MKV's)  did overload, the overload was a desense or composite noise 
type sound. It would take out noise floor signals worse, be progressively 
less problem for stronger signals, and never be bothered with any antenna 
combinations with strong signals. When the SDR overloaded, it was just 
totally gone for everything, and wider frequency spacing with the local TX 
made absolutely no difference like it does with a normal receiver. I assume 
this was from overflowing the ADC, but it was a very dramatic sounding 
overload.


That, coupled with the fact it did not have a traditional knob and panel 
system and had some transmitter spurs, made it useless here. But that was 
this setup and this application, where a local 1500 watt transmitter within 
a few thousand feet of the RX antennas was being used while receiving. This 
was a single transmitter multi-op, where one TX signal was allowed on the 
air at a time but two or more operators were making contacts.


I still never find any SDR I listened to, even that one without a 
transmitter running, better than analog detection for my ears on 
"in-the-noise" signals.


73 Tom








- Original Message - 
From: "Steve Ireland" 

To: 
Sent: Monday, October 19, 2015 8:07 AM
Subject: Re: Topband: ADC Overload from MW transmitters



Hi Jim

Clearly in a large US city, there is going to be a whole larger degree of 
difficulty than here.


Perth is still pretty much a small city in world terms, with a population 
of about 2 million. In addition to the ABC transmitters, we have about 
half a dozen other transmitters, but only two of these have signals of any 
size – 6PR (10kW) and 6IX (2kW), with the former of these putting in the 
largest signal to me, with its transmitter/antenna on the banks of the 
Swan River estuary about 15km away.


When I used my HPSDR, originally I had no filtering in front of the ADC 
and had some overload problems on 160m from the local BC stations. 
However, a simple Chebyshev HPF got rid of this. Later when I added the 
Alex bandpass filters, which are part of the HPSDR design, there was no 
longer any need for the HPF.


The main point, as Phil says in his post, is that the amount of protection 
an ADC is going to need will vary widely, depending on factors such as 
local AM BC transmitters and how strong they are. In my case, all I had to 
do was to use the general coverage facility of the SDR to look at the 
medium wave here, see which of the signals were largest and look for a 
suitable HPF design accordingly .


Vy 73

Steve, VK6VZ



That's typical of medium-size cities in the US for high power 
broadcasters, but major cities typically have twice as many. Both large 
and medium-size cities, as well as smaller ones, typically have 6-10 
stations in the 5kW range, and more in the 1kW range. Chicago is typical 
of a large city (like New York, Boston, Los Angeles, San Francisco) -- it 
has 50kW on 670 kHz, 720 kHz, 780 kHz, 890 kHz, and 1,000 kHz. There's 
also a daytime only station with 50kW on 1160 kHz. Cincinnati is typical 
of smaller cities like Indianapolis, Detroit, Minneapolis, Cleveland, St 
Louis, and New Orleans, with 2-3 50kW stations and many smaller ones. 
Cincinnati 50kW stations are on 700 kHz and 1530 kHz.


I grew up in a small town in WV, with three 5 kW stations within two miles 
on 800 kHz, 930 kHz, and 1470 kHz.


Bottom line -- there's a lot more broadcasting in the US than in most 
countries.


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Re: Topband: ADC Overload from MW transmitters

[Tom W8JI]

I'm still of the opinion --right or wrong-- that there will *always* be
hams using analog technology that will be able to out-hear anyone using an
SDR (even DDS) to copy very weak CW signals at the low end of 160. *But I
have an open mind.* I think it was Barry N1EU that disagreed with me on
that (I think he has an Anan DDS SDR). But we need people like him that
drive us to investigate SDR further. :-)


I think it depends on the individual. If an individual has the mental 
ability to "process" noise out of the signal, external filtering and "noise 
reduction" won't mean nearly as much. Some people I've operated with are 
better than I am, some the same, and many others just cannot hear the 
signals unless they are crystal clear.


I'm poor at SSB, but good at tone.

My first experience with this was when a group of people came over to pick 
me up to go to the Cincinnati hamfest. I was working VK's on 160 (using a 
modified SX101) through heavy noise, copying the callsigns fairly easy, but 
no one else could even tell there were signals.


Another case was at Dayton, when MFJ was demonstrating a DSP. I could hear 
the signals the same with or without the DSP, and people walking up were 
marveling. Others walking up couldn't hear the difference.


When a human is part of the decoding system, results will vary.

A similar thing is true for results at different stations, when we talk 
about overload. One size does not fit all applications. I see now where the 
one station's comments about a bunch of modest signals overloading an SDR 
kicked off the "popular folklore" rebuttal, but 1500 watt transmitters into 
antennas less than 2 wavelengths from an RX antenna are not the same as 
something far out of band one or more miles away.


We have to read carefully, and not mix cases.   :)

73 Tom 


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Re: Topband: ADC Overload from MW transmitters

[Tom W8JI]

If there is one transmitter per band and no duplex, I think it would work 
fine. (If you can get old timers to use knobless radios.) External filters 
would easily correct any problems.


The issue is duplex on one band at high local signal levels, where an 
external filter would be much too complicated.



- Original Message - 
From: "bruce whitney" <zuce...@yahoo.com>

To: <topband@contesting.com>; "Tom W8JI" <w...@w8ji.com>
Sent: Monday, October 19, 2015 11:59 AM
Subject: Re: Topband: ADC Overload from MW transmitters


This has been an interesting discussion.
I heard a rumor that a very prominent and successfully competent multi-multi 
contester in IL was going to an all SDR multiple computer control set-up. 
Which would seem to be problematic in light of this discussion?

Anyone else hear this?
Bruce W8RA

--------
On Mon, 10/19/15, Tom W8JI <w...@w8ji.com> wrote:

Subject: Re: Topband: ADC Overload from MW transmitters
To: topband@contesting.com
Date: Monday, October 19, 2015, 10:58 AM

I think the problem here is some
people read this as a SDR radios never
overload, or are superior in every case.

Apparently one person thought they were junk because
multiple modest
strength signals would add up to overload them, and that
triggered the
response that was misinterpreted to mean they never overload
under any
condition or were always superior to roofing filtered
systems common in
standard receivers.

In the case I had here, a *single* transmitter totally wiped
the SDR out.
The overload was nothing like the desense or noise in a
traditional
receiver. It just was totally useless. It was useless at any
signal spacing,
because it had no front end selectivity at all that would
reduce levels.

For my application, it was useless. It was far worse than a
K3, which a few
kHz spacing would duplex on most antenna combinations. When
the K3 (or
FT1000MP MKV's) did overload, the overload was a
desense or composite noise
type sound. It would take out noise floor signals worse, be
progressively
less problem for stronger signals, and never be bothered
with any antenna
combinations with strong signals. When the SDR overloaded,
it was just
totally gone for everything, and wider frequency spacing
with the local TX
made absolutely no difference like it does with a normal
receiver. I assume
this was from overflowing the ADC, but it was a very
dramatic sounding
overload.

That, coupled with the fact it did not have a traditional
knob and panel
system and had some transmitter spurs, made it useless here.
But that was
this setup and this application, where a local 1500 watt
transmitter within
a few thousand feet of the RX antennas was being used while
receiving. This
was a single transmitter multi-op, where one TX signal was
allowed on the
air at a time but two or more operators were making
contacts.

I still never find any SDR I listened to, even that one
without a
transmitter running, better than analog detection for my
ears on
"in-the-noise" signals.

73 Tom








- Original Message - 
From: "Steve Ireland" <vk...@arach.net.au>

To: <topband@contesting.com>
Sent: Monday, October 19, 2015 8:07 AM
Subject: Re: Topband: ADC Overload from MW transmitters


> Hi Jim
>
> Clearly in a large US city, there is going to be a
whole larger degree of
> difficulty than here.
>
> Perth is still pretty much a small city in world terms,
with a population
> of about 2 million. In addition to the ABC
transmitters, we have about
> half a dozen other transmitters, but only two of these
have signals of any
> size – 6PR (10kW) and 6IX (2kW), with the former of
these putting in the
> largest signal to me, with its transmitter/antenna on
the banks of the
> Swan River estuary about 15km away.
>
> When I used my HPSDR, originally I had no filtering in
front of the ADC
> and had some overload problems on 160m from the local
BC stations.
> However, a simple Chebyshev HPF got rid of this. Later
when I added the
> Alex bandpass filters, which are part of the HPSDR
design, there was no
> longer any need for the HPF.
>
> The main point, as Phil says in his post, is that the
amount of protection
> an ADC is going to need will vary widely, depending on
factors such as
> local AM BC transmitters and how strong they are. In my
case, all I had to
> do was to use the general coverage facility of the SDR
to look at the
> medium wave here, see which of the signals were largest
and look for a
> suitable HPF design accordingly .
>
> Vy 73
>
> Steve, VK6VZ
>
>
>
>> That's typical of medium-size cities in the US for
high power
>> broadcasters, but major cities typically have twice
as many. Both large
>> and medium-size cities, as well as smaller ones,
typically have 6-10
>> stations in the 5kW range, and more in the 1kW
range.

Re: Topband: FW: Commond mode choke for Beverage

[Tom W8JI]

I tried 7 & 8 turns, but it resolved too high in freq.



Use 9 TURNS on a core-stack of five (5) of  P/N 2631803802 cores. That’s 
the Mix #31 core.



The attenuation of any choke significantly depends on the common mode 
impedance, and impedances from shield to ground. Many times just a few ohms 
is enough, some cases even 10,000 ohms will not help.


It is a system that varies from place to place. For example, if you have a 
small floating loop the common mode impedance of that loop is already so 
high a choke would have no effect at all. If you have a cable between two 
fairly well grounded points, if it even needs a choke, the choke requirement 
would be low.


It is almost like a pi network filter. There is a shunt impedance at one end 
of the choke, the choke impedance, a series line common mode impedance, and 
another shunt impedance.


A dipole is another example. If the feed cable to a dipole is 1/8th to 3/8th 
wave long with a cable suspended away from things, and it is grounded at the 
earth, it is just as effective as using a balun. If you added a common mode 
choke near ground, it would make common mode significantly worse.


Before going wild with impedance goals, it is a good idea to look at the 
particular system.


My Beverage RX antennas at the antennas are isolated from the cable shield 
because I have just a few short ground rods. I don't want the shield being 
be a ground for those poor ground rods, because the shield would couple in 
unwanted signal. My RX verticals out in a field each have 8 long radials and 
buried feed cables, and the hub is well grounded. They have no common mode 
isolation at all, and do not need any.  Any contribution of signal by the 
coax would be no different than just adding another radial.



73 Tom

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Re: Topband: SDR Mythbusters - ADC Overload myths debunked...

[Tom W8JI]

The opinion expressed in the Flexradio editorial about noise blankers 
being

completely harmless, is not an opinion, it is even false.



It really isn't an accurate or factual technical article. It is a sales 
brochure meant to enforce the love each of us have for a particular system, 
in this case the magic of SDR. You might as well read an MFJ advertisement 
for technical accuracy, watch a year old VW diesel commercial, or listen to 
a politician of any party telling us how they will fix everything. It is all 
sales and stoking people's emotions or existing opinions, with just enough 
truth woven in to avoid prison.


Oddly, the K3 Elecraft is largely SDR. It is an SDR receiver with a standard 
analog front end as a frequency converter with roofing filter. IMO, the 
worse part of the K3 is the SDR part.


Try this test. Poll users who work very weak CW signals routinely in all 
sorts of station environments, just the general population of weak signal CW 
DXers.  Ask them if analog detection is better for pulling a weak signal 
below noise floor out of noise, or if a DSP detection system is better.  The 
results are always that DSP detection systems are viewed unfavorably over 
good analog systems by significant number of people.


The limits of this case are digging weak signals, that are at or below 
noise, out of the noise.


There is always a certain loss of dynamics to me, when I listen to any SDR. 
It has been this way for me with any SDR or DSP detection radio. Something 
my ear depends on to know the difference between a signal below noise and 
just noise without signal is lost in every single DSP detection system I 
listen to. It melts the signal into the noise with a distortion.


We did a blind A-B test (I have audio lines that bring every receiver to a 
jack ). It is easy to tune two receivers to the same signal, and have 
someone else switch the lines.


People who cannot copy below noise signals seem to not notice this effect.

73 Tom 


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Re: Topband: Bandpass filters for receive antennas

[Tom W8JI]

Where can I find a schematic for a good high pass filter that rolls off at
1700 kHz?

I can't even have back to back diodes here on Beverages without amplifiers, 
because the accumulation of hundreds and hundreds of BCB stations sum to 
more than two volts peak.


With a 10dB gain amp, I can light 12 volt lamps.

I cure this with a very simple basic 5 pole filter that has 3dB roll off at 
1600 kHz. Unless you have something on top of you at upper AM BCB, you don't 
have to worry about 1700 kHz plus.


You need two inductors and three silver micas, and get a good preamp. Do not 
put it at the antenna. It just adds to overload issues. My amps are all in 
the shack, and some of the cables are 3000 foot long mixes of F6, F11, and 
only a few have significant hardline runs. 


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Re: Topband: SDR Mythbusters - ADC Overload myths debunked

[Tom W8JI]

On Sat,10/10/2015 2:15 AM, Steve Ireland wrote:
Of course, I was talking about using a DUC/DDC in a single 
transmitter/receiver urban/semi-rural station setting on a quarter to 
half an acre block, which is the setting in which the vast majority of 
people who subscribe to this reflector would be using a transceiver.


Your use is not nearly so much a majority as you might suspect. A fair 
percentage of contesters operate SO2R. MANY hams live in proximity to high 
power broadcast stations. Hams with good antennas in locations exposed to 
many in-band and out-of-band signals are likely to encounter far higher 
voltages at the input to the radio than you do.


I thought they were talking about overload from local transmitters.

If you look at Sherwood Engineering's tests, they show the problem we had. 
The wide spaced dynamic range of SDR's is only 96-99 dB.


The wide spaced dynamic range of the K3 is up around 105 dB. That 5 or 10 dB 
is helpful with local transmitters, but the real difference we noticed was 
the SDR just totally goes goofy when it overloads, losing everything, while 
the regular receivers just "noise up" or de-sense.


Overload characteristics for strong signals have nothing to do with how a 
receiver works without strong signals to overload it.:)


73 Tom 


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Re: Topband: SDR Mythbusters - ADC Overload myths debunked

[Tom W8JI]

None of the below has anything to do with overload from local transmitters. 
:)


Or did I miss that part?

- Original Message - 
From: "Steve Ireland" 

To: "Topband reflector" 
Sent: Tuesday, October 06, 2015 9:51 PM
Subject: Re: Topband: SDR Mythbusters - ADC Overload myths debunked



G’day all

As someone who has extensively used a digital down conversion/digital up 
conversion transceiver (original HPSDR) on the Topband, it is good to see 
this myth being debunked publicly as much as possible. Another station who 
has used an HPSDR even more extensively than me on Topband is Greg ZL3IX, 
who may be interested in commenting.


For about 18 months I used the HPSDR transceiver alongside a ‘benchmark’ 
Elecraft K3 in contests and for DXing, alongside keen contester/DXers 
VK6LW (about 3km away) and VK6DXI SK (about 30km away) running full power 
on Topband and the other bands.  I could work equally close (within 500Hz) 
to Kevin and Mirek on the HPSDR as I could on the K3.


The brick-wall sided constantly variable filtering provided by the fully 
digital HPSDR and its associated OpenHPSDR software and the way this 
filtering handled noise in comparison to the K3’s digital filtering made 
the HPSDR a superior radio for weak signal DXing – simply put, I could 
read S2/S3 signals on the HPSDR in a 50Hz bandwidth that were unreadable 
on the K3.


The only problem for me is that using computers day in, day out at work, I 
loathe using them for radio and hate spending my evenings fiddling around 
with software, so the HPSDR has finally gone (mind you, so has the K3 – 
loved the radio but hated the audio and went and bought an old Orion 2 
which sounds waaay better to my ears).


DDC/DUC radios handle strong signals as well as the best of analogue 
radios – the only question for topbanders is whether you like their 
ergonomics and the whole idea of having a digital radio.


Vy 73

Steve, VK6VZ


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Re: Topband: BOG question

[Tom W8JI]

Frank et. al,
The ground does indeed affect the Vf however different types of 
wires/cables are affected differently and the only way to know for sure is

to measure the Vf yourself. I use old telephone cable (


None of it, including the cable type, affects the spacing of elements. That 
was Frank's point, and that was all he ever said.


Somehow what Frank said was misconstrued into meaning something about the 
transmission line mode of waves in the antenna itself, which no one ever 
disagreed about. We all know, or should know, the Vp through the length of 
the antenna is affected by ground and dielectrics.


Frank's statement was that the external wave was not affected by the Vf in 
the antenna, so the required spacing does not change between a BOG and any 
other antenna. 


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Re: Topband: BOG question

[Tom W8JI]

I believe there is a large influence of height above ground on VF.
From a theoretical basis, this has been "known" since Wise's classic paper 
"Propagation Of High Frequency Currents In Ground Return Circuits" (1934).
This was experimentally verified in the Litva and Rook report from the CRC 
(Canada), and compared with theoretical results.
These guys didn't extend their calculations to right-on-the-ground 
antennas. The attached (if it gets through the server) is from a 
spreadsheet of mine based on the Wise equations. The influence of height 
on VF is very very pronounced.

Chuck


Frank is absolutely correct in what he said.

The velocity factor decrease in the Beverage has nothing to do with the 
arriving wave velocity that affects the required phasing spacing.  The wire 
looks longer because the earth slows the wave ***in the wire's transmission 
line mode***. The required spacing and stagger is set by the wave, not the 
wire. It is the same in a BOG, a normal Beverage, or in a vertical.


The broadside spacing, to increase directivity a useful amount, has to be up 
around 1/2 wave or more. The end-fire or echelon spacing has to be the same 
as a normal Beverage, or vertical, to have useful directivity increase.


The only thing the earth does is slow the velocity in the transmission line 
formed by the wire and earth image. The antenna cannot be a long as a 
regular Beverage because of the slowed propagation in that "transmission 
line". It is little different than loading the wire with any lossy 
dielectric.


While the antenna is limited to less length because of velocity factor in 
the wire's transmission line mode, the fact it is a BOG has no bearing on 
the wave velocity, or the required spacing or stagger.


73 Tom 


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Re: Topband: BOG question

[Tom W8JI]

I think this is a wording issue. We all understand the difference between 
VF in the transmission line and VF in free space.
What caused difficulty was the term "arriving at". I took this to mean "at 
the antenna" not free space, as there's no need to mention the antenna if 
the desired meaning was "free space".

Chuck


Frank said:

"Signals arriving at the BOGs are not travelling in the ground, therefore
their velocity of propagation (Vp) is unaffected by the ground. "

That seems OK to me. I can't think of a better way to say it, but maybe 
someone else can.


The Beverage antenna itself, just like any antenna, is also a transmission 
line. The only significant change in velocity factor by laying the antenna 
on ground is in transmission line mode characteristics of the BOG. The 
signal arriving at the antenna and in space all around the antenna is not 
any more affected by the ground than it would be with any other antenna.


The same effect could be simulated by a series inductance distributed along 
the antenna, or a dielectric. It isn't the signal around the antenna or 
arriving at the antenna that is changing, it is the transmission line mode 
of the antenna as the signal passes along through the wire.


73 Tom 


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Re: Topband: K1FK to JA Via 160-Meter Long Path

[Tom W8JI]

In the summer, I often worked far northern Europe east or south east at my 
sunset. Sometimes it is day after day.


I've worked some far east Asians, but not Japan, east or south east at my 
sunset.


Where it is dark or almost dark, the signal might go. 


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Re: Topband: DX Engineering 4-Square RX Antenna: Element Amplifiers?

[Tom W8JI]

~  .5 dB might make as much as a change from 25 dB F/B to 20 dB. I wouldn't 
expect it to be noticeable.



- Original Message - 
From: "Jeff Maass K8ND" 

To: "Topband Mailing List" 
Cc: "'Jim Galm'" 
Sent: Tuesday, September 22, 2015 9:15 PM
Subject: Topband: DX Engineering 4-Square RX Antenna: Element Amplifiers?


In January, Jim W8WTS and I were at PJ2T for CQWW 160 CW, and we both 
noted

that our DX Engineering 4-square RX antenna did not appear to perform as
well as usual. It is a 98-foot configuration using 102-inch whips.

It is set up "field day style" for contests when we use it (i.e. not set 
up
permanently), and so we thought that perhaps all the handling over the 
years

might have caused problems with the feed and delay cables. We had a Array
Solutions AIM-4170C VNA with us, and confirmed that all the cables were
still  in good shape and were of the correct lengths.

We decided to bring home the four DXE ARAV3 active antenna amplifiers to
diagnose at home (we left the four whips on Curacao!). W8WTS has an Array
Solutions VNA-2180 2-port device, and captured curves for inputs and
outputs. His analysis is shown below. Screen captures of the resulting
curves are in an archive at:
http://www.k8nd.com/Radio/PJ2T_DXE_4-Square_amps_ photos.zip
 .



"Each amp has a port a sweep and a port b sweep.  There is also a 
reference

pair of sweeps with the amplifier jumpered out of the circuit, to verify
that the ports are calibrated correctly.  The port a sweep shows the
impedance looking into the antenna port.  We want the input impedance to 
be

extremely high; higher is better.  There is a peak in the Z because of the
parallel LC filter on the input of the AVA-2 that rejects out of band
signals.  You can see that they are all set correctly to peak on 1.8 Mhz.



"The port b sweep shows the magnitude and angle of S21.  S21 is the 
forward

voltage gain of the amplifier.  We want the forward voltage gain to be
exactly 1, which is shown on the graphs as 0 dB.  The four amplifiers have
different gains at 1.8 MHz, but they are very close.  The lowest is amp 1 
at

1.2 dB and the highest is amp 4 at 1.4 dB.  A gain difference of 0.2 dB is
very small, but it might make a difference. "



They appear to be working OK, but what we don't know is:

 QUERY: How much of a gain discrepancy is tolerable in the element
amplifiers in a DXE four square?

73,  Jeff  K8ND

















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Re: Topband: Waller Flag Question

[Tom W8JI]

I would just like to understand what Tom is saying. I almost think he had
noise figure confused with noise temperature at one point.

Correction to my previous e-mail, first sentence in second paragraph.
should have said "When I studied preamps and NF ~30 years ago, I thought
the NF of the first active device (preamp) was the all-important thing".



With proper conversion, noise figure, MDS, and noise temperature are 
interchangeable in overall use or meaning.


People in this thread are working in noise figure and gain when considering 
preamplifiers, so I stayed there.


40 dB is a whole lot of gain in front of a normal receiver. To me, it looks 
like the 40 dB is unrealistic unless the receiver is lacking normal gain. In 
a common receiver, if 40dB gain is required, the antenna system is going to 
be more difficult to deal with than almost all can handle.


I'm only specifically speaking about the amount of gain. Don't read more 
into this than specifically what I am saying. (Which people have a tendency 
to do.)


73, Tom 


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Re: Topband: Waller Flag Question

[Tom W8JI]

Tom,  I'm afraid I disagree but agree with some of  that, I am using a 
43dB
gain preamp since 2010 with not a single failure yet, but I understand 
your
point. It is so delicate to implement that most of fellow that try it 
fail.

Even aluminum enclosure does not shield it enough, 40 dB gain is 10.000
voltage gain, it needs a dual shield with steel to cut magnetic field, the
feed lines must be decoupled over 80 dB, relays must be 100dB or more in
isolation, and much more details that I won't cover.

It is not a weekend project.



JC,

The problem is gain and noise figure, not shielding.

Let's assume a receiver with 250 Hz bandwidth has a MDS (3dB S+S/N) of -135 
dBm. This is a 15 dB receiver noise figure.


A 0.5 dB noise figure front end amplifier with NO other losses would 
produce -149.5 dB MDS. That is the absolute maximum MDS sensitivity 
obtainable with 250 Hz BW and 0.5dB total input noise figure.


If we include the receiver's noise figure, 14.5 dBm gain would result is a 
system composite noise figure of 3.44 dB. Increasing amplifier gain (with no 
change in amplifier 0.5 dB noise figure) results in the following system 
composite noise figures:


14.5dB = 3.44 dB
20 dB =  1.55 dB
25 dB =  0.86 dB
30 dB =  0.62 dB
35 dB = 0.54 dB
40 dB = 0.51 dB

At someplace around 20-25 dB, you get into system limits. The improvement 
from 30 dB to 40 dB is only 0.11 dB. No one will notice that.


This of course varies with the receiver, but few receivers are worse than 
this example.


Let's say we have an input stage NF of .5 dB with 15 dB gain. In order to 
have a cascade NF of .7dB the second stage has to have about a 2 dB NF.


All of this is peanuts.   A .6dB noise figure is a 3 dB MDS of -149.4 
dBm, while a 2 dB NF is a MDS of -148 dBm with 250 Hz BW.


There is a point where inevitable system flaws make using an antenna with 
such negative gain to require less than 1 dB NF impossible for "copy this 
plan".  This is why Beazley's out-of-phase small horizontal elements were 
mostly met with didn't work. The problem with models is we can build perfect 
systems that we cannot repeat in the real world.


Again my example of the small commercial loop I have. It limits by loop 
internal noise by many  dB at my location, and common mode on the cable is 
very evident. If I moved the same antenna to a location with 20 dB more 
external ambient noise floor, it would limit on external noise.


It seems unlikely most compact antennas are being used in locations so quiet 
they need 30 dB gain, or .6 dB NF.   If they had room, they would not have 
as much ambient site noise.


I'm not being disagreeable, just describing the practical limits.

73 Tom 


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Re: Topband: Waller Flag Question

[Tom W8JI]

Thank you, JC:

I don't know where this coming from ,but the gain you need for a VWF 
modest
size is 20db for vertical polarization and for horizontal HWF you need 
40db

on 160m, on 80m divide this by 2, you need only 20 dB  and on 40m 10 dB a
NORTON preamp is enough. All situations you need a band pass filter.



20 dB is a realistic gain figure.

The very low sensitivity of horizontal polarization, because at low heights 
in wavelength the earth "shorts the electric field", and because at low 
heights the earth's reflection nulls the antenna peak response, causes great 
difficulty.


If local site noise is high, and if care is taken in balance, the horizontal 
system can be built but 40 dB gain is unlikely to be needed unless the 
receiver is dead.


The reason is pretty simple. Most receivers are in the minus 130-140 dBm 
noise floor range. If you added 40 dB gain to that, the noise figure of the 
required front end would be an impossible negative noise figure in the -20 
dB or more noise figure range. Of course anything less than 1 dB is very 
difficult, and below 1/2 dB starts to be impossible. Even if you obtain that 
noise figure, cable leakages and common mode would overwhelm the low antenna 
level.


20 dB is about the limit for most receivers, although a dead receiver could 
use 40.  If the receiver is stone deaf, 40 dB would allow a workable noise 
figure at the front end.:-)


This low sensitivity is why K6STI's antenna met with such limited reports of 
success.  If the site is very noisy with local distant noise, then the 
antenna's noise floor is high enough to limit system noise floor. Otherwise, 
the cables and input amplifier would set noise floor.


I have a similar thing here with a commercial loop antenna. Even though 
vertically polarized, it is noise limited at my location by internal 
amplifier noise.  Now if I move it into a noisy location, it limits by 
outside noise.


No matter what we try to do, we are not going to have a 0 dB noise figure. 
When we start making the antenna sensitivity so low it requires gain with a 
normal receiver so unrealistic that it limits on the front end noise, it is 
useless. What good would seeing the S meter at S-2 or S-4 from amplifier 
noise do?  That is what the popular commercial loop I have does. In a quiet 
location, it limits on its own internal amplifier noise. Six dB less gain 
does not change S/N ratio one bit.


We should all question systems that need 40dB with normal receivers. 20 dB 
is more rational.


73 Tom 


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Re: Topband: Waller Flag Question

[Tom W8JI]

Thanks for the insights.  I have no doubt the theory is correct.  My sense, 
though, is that in the denser suburbs, we live in a "fog" of local radio 
noise, generated by the scores of digital and other devices that surround 
us.  A similar observation was made 20 years ago by Brian Beezley, K6STI, in 
a  QST article titled "A Receiving Antenna that Rejects Local Noise" 
(September, 1995, page 33):  I've been looking around for something that 
might work better than my present antenna, and I see good reports about the 
Waller flag from people who are actually using it.  So I'll give it a try 
and see how well the theory matches up with actual practice.  That's what 
ham radio is all about -- no? 


You said earlier:


The on-line materials about Waller Flags says that a modest size WF would
need about 40 dB of gain to boost the signal to a usable level.  One of
the postings says that cascading two preamps of 20 dB each seems to add
extra noise, and they talk about developmental work being done on a single
preamp of 40 dB.




I'm not sure where "need about 40 dB of gain to boost the signal to a usable 
level" comes from.


40dB is an unworkable amount of gain, unless the basic receiver is deaf. 
Here is an example:


An Elecraft K3 has about -138 dB noise floor with preamp on.  40 dB more 
gain, or -178 dBm noise floor, would require a preamp noise figure of  -18dB 
at 250 Hz BW and -24 dB NF at 1 kHz BW by my calculations. That's 100 times 
less noise than no noise.   :)


Maybe the reason people can't get two preamps cascaded to work isn't because 
it is two separate amplifiers, but they are trying to do something 
unnecessary and impossible? It seems to me 20-25dB would be more than enough 
for most receivers.


73 Tom 


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Re: Topband: Waller Flag Question

[Tom W8JI]

The on-line materials about Waller Flags says that a modest size WF would 
need about 40 dB of gain to boost the signal to a usable level.  One of 
the postings says that cascading two preamps of 20 dB each seems to add 
extra noise, and they talk about developmental work being done on a single 
preamp of 40 dB.


Is there now such a 40 dB preamp?  Is it made commercially? 
Alternatively, are there plans on-line somewhere?  Has someone actually 
used it in a high-RF urban/suburban area, with multiple 50 kW AM BC 
stations?  With what results?




At some point we have to be realistic.

A typical receiver is somewhere in the -130 dBm sensitivity range, depending 
on bandwidth and other things.


At -140 dBm and 250 Hz noise bandwidth, the system would require a 1 dB 
noise figure front end.  That's about 35 deg K noise temperature.


If you need a 40 dB amplifier (or even close to 20dB) into a normal good 
receiver, you will never get the noise temperature of things in front cool 
enough to let external noise set noise floor. The issue isn't connecting two 
amplifiers in cascade, the issue is the limit of noise temperature.


The only place negative gain antennas that require more than ~ 20 dB gain 
with a normal receiver at a quiet location will work into the external 
ambient noise floor generated outside the antenna is in a location blanketed 
with strong local noise.  Besides that, if the gain is so far negative the 
coaxial cable will easily become more of an antenna than the thing we call 
an antenna.


40 dB gain in front of a receiver is pure fantasy, unless the receiver is 
dead as a door nail.


73 Tom 


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Re: Topband: Bandpass filters for receive antennas

[Tom W8JI]

Bandpass filters do nothing for in-band signals -- their only function is 
to reject OUT OF BAND signals. The primary reason for using bandpass 
filters IS for RX. A good 160M bandpass filter would be effective at 
reducing overload from AM broadcast stations. So would a high pass filter. 
There is a survey of bandpass filters for contesting at this link. 
http://k9yc.com/BandpassFilterSurvey.pdf


I use a high pass filter for rejection of the AM BCB band. Between 70 and 
80% of the net power (or voltage) into my RX system comes from distant AM 
BCB signals.


Without a small 5-pole highpass that starts to roll off at 1700 kHz, I can 
connect a  miniature 12V 50 mA incandescent lamp (like the MFJ 1025 uses as 
a fuse) and it illuminates a dull red.


This is with no attempt at matching power to the filament cold resistance.

My system can be bothered by the sum of all those thousands of signals, I 
add a BCB high pass, and then I can run 1500 watts and not bother my own RX 
when transmitting on 80 or 40 while receiving on 160. Of course I have 
500-2000 ft separation on antennas, but this still shows how a bunch of 
small signals can add up to disaster if they hit something non-linear before 
being filtered.


Always remember there are two problems. One is the absolute limit of in-band 
signal a receiver system can take. The other is the absolute limit of the 
sum of all the signals entering an overload sensitive point in the system.


Less than one volt peak line voltage is not enough headroom to prevent IM 
products in a reasonably good system. Back-to-back parallel diodes are fine 
for Sky Buddy receivers and FT101's. A single diode opposing another diode 
in parallel will clamp at about 6 dBm if your receiver looks like 75 ohms. 
Almost all receivers will conservatively take 15-20 dBm, or 2-4 volts peak, 
at the antenna port in band.


If you have a good system, you'll want something other than back-to-back 
diodes.


73 Tom 


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Re: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)

[Tom W8JI]

The Array Solutions device also uses the transformers to increase the
voltage at the diodes then steps it back down which means that the diodes
are not doing their limiting at 50 ohms.   Therefore, your set of 2 series
diodes or even one diode each direction is limiting at a higher power 
level

than the Array Solutions device.

From the QST article.
"The transformer increases the voltage level to allow limiting by a pair 
of
back-to-back diodes and then another transformer matches the output to a 
50

ohm receiver input."


Here are the problems:

1.) The peak voltage at 75 ohms and 100 mW (20 dBm) is almost 4 volts.

2.) Receiver impedances are all over the place. I've seen them as low as 20 
ohms, and as high as 150 ohms. Most of those I measured are closer to 40-80 
ohms.


3.)  The voltage at the diodes is the vector sum of all signal voltages. If 
you have a wide band antenna, there can be considerable net voltage from 
many hundreds of small signals summing. I can light a 12V filament lamp dull 
red off my Beverages at night, and I am 30-40 miles from the closest active 
AM BCB station. It is the sum of hundreds of signal from hundreds of miles 
that is the problem.


4.) Receivers limit the signal range to something centered around the 
selected band, so they don't see that wide swath of summed voltages. The 
diodes in a limiter do.


5.) The miniciruits transformer mix and create IMD, and are very sensitive 
to dc current, even at pretty low levels. The point where they add IMD is so 
unpredictable compared to limiting, they are not a good choice in receive 
systems. This is especially true when you have no idea how many hundreds of 
signals that transformer has to process at the randowm receive systems in 
the field. (I tried them for antenna and amplifiers and abandoned them back 
in the 70's. My eight element look antenna array initially used them, but 
the LORAN signals and AM BCB signals killed them).


The last thing in the world useful for RX protection is a soft limiter. It 
has to be a hard clamp, set just safely below whatever RX port voltage might 
threaten equipment. No clamping or distortion until that point. Premature 
limiting does absolutely no good, and potentially many bad things.


If you pay thousands of dollars for a receiver that has a wide spaced 
dynamic range of over 100 dB, why would want to make it into 1970's Yaesu 
FT101 performance with a limiter? Remember, this is not a few signals in the 
passband. The diodes are pre-filter, and they clip at the sum of all the 
hundreds of small signals across them.


If you use diodes, they become more acceptable is a modest amount of 
pre-filtering is used to keep needless signals (especially the AM BCB) out.


73 Tom 


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Re: Topband: FRONT END SAVER

[Tom W8JI]

There is nothing magical about a front end saver, IMHO.  Several years ago 
I built my first, a simple unit employing a pair of Panasonic PCB-type 
relays which grounded both the RX antenna port on my transceiver and the 
beverage antenna input to the preamp/switching system on transmit.  As 
long as you do not intend to use full break-in this system works very well 
and costs peanuts to build; after some 15 years running a KW or better no 
problems have ever occurred, and I have duplicated this simple design at 
other stations.




Hi Bill,

It is easy to assume there is nothing critical about a front end saver (a 
poor name in many applications) when we think we have one that works, but it 
does a lot more than saving the front end.


Besides preventing damage, it also keeps radios from generating clicks and 
spurious signals.


Some radios and installations do not need these systems, some do.  Some 
systems not needing them (or being critical) doesn't mean they are all not 
critical.


They are system dependent for antenna types, antenna physical layout, radio 
type, and power level.


73 Tom 


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Re: Topband: KD9SV-OK1RR relays ???

[Tom W8JI]

I added a BNC female connector in the rear panel of my old Yaesu, FT747 (It
is an FT80C, the commercial version with metallic chassis) few months ago.

I was using that BNC to feed an SDR receiver using the same antenna.

If i add a SPDT switch also on the rear panel and RE-WIRE the BNC connection
i can get an RX port in my old radio and can connect an RX antenna...like
modern radios...Switch Pos A (main antenna at SO239)...Pos B (SO239 for TX
and BNC for RX)...i made few mods to my radio, so, i know it very 
well...


There you go. That is a good solution. Now you know you cannot directly 
transmit into the receiver antenna.


Once you do that preventing excessive RF voltage back into the receiver is 
much easier, but it still requires an fast system. I would also use a hard 
clamp system and fuse for level, not just a single relay.


For just a very few extra components, it can be hundreds of times more 
reliable! When we get so much for so little, it is worth considering. When I 
see a front end saver without a fuse or clamp system, I know it is not a 
safe design.


73 Tom

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Re: Topband: KD9SV-OK1RR relays ???

[Tom W8JI]

I'm not sure goosing the pull-in voltage is always a good idea. It may
shorten the initial closing time a bit, but (depending on the relay)
it can aggravate contact bounce, doing more harm than good. It also
stresses the relay.



Done properly, it doesn't hurt a thing. The proper way is to use current 
limiting.


It is safe to run 50 volt supplies on most 12 volt relays, but there is a 
point of diminishing returns on speed. The high initial voltage ramps up the 
magnetic field faster, but it does not cause excessive heat or current. This 
is because the relay starts at near zero mA from inductance.


None of this matters, though. Using a relay on make for protection is a bad 
idea. The de-active state should be used for protection, and the active 
energized state used to allow RX. 


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Re: Topband: KD9SV-OK1RR relays ??? (RX Front End Protector)

[Tom W8JI]

That's similar to mine, but mine has two 1N4148 diodes in series,
back-to-back, total of four diodes.

However, after I did that, I got to thinking that it would be better with
only two. Or that there was no need for four. (Don't ask me to explain,
it's been a long time since I've thought about that.)


You probably used four diodes for a good reason.

20 dB is 2.73 volts RMS across 75 ohms. That is 3.86 volts peak.

If you use back-to-back diodes, the system clamps at .7 volts peak and mixes 
at lower levels. That's like 5-10 dBm or less for the sum of all signal 
power.


Remember that clamp is seeing the vector sum of voltages from ALL the 
signals on the RX antenna, not just signals on the band you are using or the 
signal you are listening to.


I can't use diodes here because of IMD, so I use a hard limiting clamp that 
is preset by a Zener diode.


Why would anyone want a clamp system that reduces the IM DR of a modern 
receiver? If you pay all that money for an RX, why not use it? I would think 
your 4 diodes are the absolute minimum to use almost any receiver's full 
dynamic range.


73 Tom

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Re: Topband: KD9SV-OK1RR relays ???

[Tom W8JI]

remember the details but it was something like hitting the relay with higher
than usual coil voltage/current and it shortened up the relay pull-in time.
It might be more complicated in this application than needed. I don't have
the URL to Measures' site but it can probably be found by a search.

The protection system should default on, not default off.  If a relay is 
used, the NC contacts should short the line or NO contacts disconnect the 
line.


It must be done this way because you do not want a connection or trigger 
failure to damage the receiver, or cause a spurious issue (which is most 
frequent). The receive antenna connection has to be allowed through willful 
application of relay voltage, not through removal of voltage.


Since the relay should be energized for RX and de-energized for transmit, 
the critical time is release time. The only way to speed release is avoid 
excessive holding current, and not use a clamp diode or any load across the 
relay coil.


The transceiver and station relay control line, which normally pulls low in 
transmit, allows relay voltage when high (transmit off). This allows the 
receive system connection by activating the RX relay.  When the TX line 
pulls low, the RX relay deactivates and  the system goes to transmit ready.


If you forget to connect the RX system control line, it all just stays 
safely in TX mode and you would notice no RX antenna. If you lose the 12V 
for the protection, it all stays in TX mode. This way you cannot operate 
without protection.


If you do it by a protection system that activates with voltage, control can 
fail a half dozen ways and you might not know. An additional benefit is when 
the station is off, the RX antenna is disconnected.


If you look at circuits in things like the MFJ1025, you will see both a 
protection circuit (a fuse lamp and diodes) and a relay that connects the 
radio to the antenna and disconnects the receive function with any loss of 
relay voltage.


We never want a protection relay that activates by application of protection 
relay coil voltage.


The whole problem is solved by just buying one of the many dozens of fairly 
fast relays. It's easy to find things in the 2-3 millisecond  range for less 
than $3.


The only issue is if the radio sequencing is good.

73 Tom 


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Re: Topband: KD9SV-OK1RR relays ???

[Tom W8JI]

 Your FT-747 only has one antenna input. It does not have a second
receiver. It doesn't even have a receive-only antenna input. You cannot
transmit and receive at same time. Why do you need a front end saver?


It needs a preamp saver or a receiver antenna saver, not a front end saver.

Any old relay will not work.

Here is what the sequence is:

1.) The radio antenna port is connected through a small relay to the receive 
preamp output, or to the receive antenna


2.) The key is closed

3.) At time X, after the key is closed, something tells the receiver relay 
to release


4.) At the same time as the key is pressed, something tells the transmitter 
to transmit. Let's call this delay time Y.


Now this is where the problem is. Many radios, especially the less expensive 
radios with a single antenna, have a Y time as short as X time. Some have X 
a little longer than Y, some have Y a little longer than X.  There is no 
guarantee without looking at the radio on ALL modes if X time is shorter 
than X.


Almost all radios are not 10mS, the relay time you suggested as a limit. 
Almost all radios are shorter than that, and some actually transmit while 
the external relay line is held low.


There is an additional problem in a few radios. There are a few radios that 
tell the relay control line to release while they are still transmitting. At 
the end of a transmission, when you stop transmitting, a few radios will 
actually turn the external circuits off **before** they stop putting out RF 
power.  I actually had to add a RF interlock in T-R relays for amplifiers 
just for those radios.


Any relay used for this application should be as fast as possible. It should 
NOT have a diode across the coil, because that slows the release time down 
considerably. I would say the safe minimum speed for most radios would be 
about a 5 mS relay transfer, including bounce. A few radios will be worse 
than that, and have almost no delay. They would require a very fast relay, 
or a sequencing system.


Some radios are designed so poorly they tell the external things to transfer 
while RF is present. Those radios cannot be fixed without external interlock 
systems.


By the way, if this does not damage the RX system, it will cause contact 
spark clicks. It will also fold some radios back into SWR protect because 
the relay transfers with TX RF applied.


The crummy interface timing in radios has been a nightmare ever since the 
first transceiver came out, and continues to be a problem today.


73 Tom 


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Re: Topband: KD9SV-OK1RR relays ???

[Tom W8JI]

It seems to me that a very fast operating preamp protection circuit could 
be
constructed employing a good fast saturating NPN switching transistor 
across

the antenna path. In receive mode the collector-base junction would have
substantial reverse bias and the transistor can be chosen for low
collector-base capacitance. With a fast switch like a 2N708 or something
similar the switching time will, of course, FAR outperform a relay closure
time.



This thread might have splintered. I was responding to this:

Your FT-747 only has one antenna input. It does not have a second
receiver. It doesn't even have a receive-only antenna input. You cannot
transmit and receive at same time. Why do you need a front end saver?


If it is a transceiver without an RX antenna point, the problem is adding a 
receive antenna to a transceiver that does not have a receive port.


If it is a transceiver with an RX port, the requirement for an external 
front end saver and what will work depends on the antennas, the power, the 
transceiver, and the antenna spacing.


A front end saver can be very simple with some radios, more complicated, or 
not needed at all.


An external switch is never easy to do correctly, unless the radio has good 
TX RX switching time sequencing.


I'm unclear what the application is, but a 10 mS relay is really too slow 
for either application. The sequencing issues I pointed out apply to both 
systems.


73 Tom 


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Re: Topband: Best wire antenna for roof top location

[Tom W8JI]

Hmmm!  Let's remind ourselves of Nuradi's situation. The roof is 110m 
high, 45m x 33 m. Corner to corner is less than a wavelength on 80M, more 
than a wavelength on 40M, but the distance to a corner from a wire strong 
between the two corners is less than a quarter wave on 80M, less than a 
half wave on 40. Assuming an ideal conductor on the roof, it's going to 
act as a reflector going upward, but the low angle pattern will be 
determined in the far field.


A dipole on a real tall building roof is worth a try (because it is so 
simple and easy), but it is not a simple predictable system.


First, any conductor approaching a resonant length in the near field is a 
real problem for antenna pattern modification. Second, another issue is 
absorption from everything in the building.  Third, there is likely noise.


A building is generally a real complicated mess of long conductors that run 
both horizontally and vertically, and thick lossy dielectrics of all types. 
A building typically cannot be modeled as a flat sheet the dimensions and 
height of the building roof. On receiving, a building is typically full of 
multiple noise sources.


There can be buildings that work OK through luck, and they are generally OK 
on frequencies where the antenna can be a long distance in fractional 
wavelengths away from the building wiring, but they are almost never 
anything like a pole or mast support for pattern, and they are rarely good 
for noise.


Usually it is a better idea to get the wire out away from things that might 
be problems, or at least put a nearfield null in the direction of the 
problem.


I had a friend who managed a high rise apartment building on a hill. We 
never could get a good 80 horizontal antenna on the roof, but it was killer 
on 20 meters and up (he had a 20-30 ft tower on the roof). The only thing 
that seemed to work well on 80 was a wire hung off the side out away from 
the building. We used the metal flashing as a ground, and end-fed a real 
Zepp antenna. It was like a J-pole laid on its side. 


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Re: Topband: [Bulk] Best wire antenna for roof top location

[Tom W8JI]

And remember -- the roof of this building is 110m, so a horizontal antenna 
is high enough to have pretty good low angle radiation!  See




Large buildings are not towers or poles. Buildings have a significant amount 
of large conductive metallic things and noise generating junk inside.


A simple vertical antenna has elevation pattern mostly determined by ground 
several wavelengths from the antenna.


A simple horizontal antenna generally has elevation pattern mostly 
determined by ground immediately below the antenna up to a few wavelengths 
out.


If the building has wiring and large connected metallic things under the 
horizontal antenna, it will act like a reflector. If the antenna is somewhat 
low to the roof (less than 1/4 wave or more above the roof), the elevation 
pattern won't be much different than a low dipole over flat earth. Most of 
the radiation will be beamed straight up.


A vertical also will have a null below the antenna, nulling building 
coupling for RF.   A horizontal has maximum possible signal into and out of 
the building. Even with a 400 ft high building, a horizontal antenna a 
fraction of wave over the roof can be very disappointing.


73 Tom 


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Re: Topband: [Bulk] Best wire antenna for roof top location

[Tom W8JI]

Some years ago, on 80 meters, an LZ station had a horizontal between two 
tall buildings and had a very strong signal.

73
Bruce-k1fz


Between buildings is entirely different than on a building roof.

Full context is important. As I said:

A simple vertical antenna has elevation pattern mostly determined by ground
several wavelengths from the antenna.

A simple horizontal antenna generally has elevation pattern mostly
determined by ground  * immediately below   the antenna up 
to a few wavelengths

out.

If the building has wiring and large connected metallic things under 
the
horizontal antenna*, it will act like a reflector. If the antenna is 
somewhat

low to the roof (less than 1/4 wave or more above the roof), the elevation
pattern won't be much different than a low dipole over flat earth. Most of
the radiation will be beamed straight up.


73 Tom



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Re: Topband: Which is best for copying the weakest DX - DSP or the ear-brain combo?

[Tom W8JI]

I'd like to know whether it's ever been established that some very 
talented

hams can out-hear the best SDRs and/or DSP available. Can a skilled
ear-brain combo (such as some highly-skilled and talented 160 meter
contesters) beat state-of-the art digital signal processing when it comes
to copying the very weakest of signals buried in the noise?


Excluding time-synchronized signal processing methods, I've never found any 
DSP system do better or do more than an analog system in signal 
readabilitly.


They are really just different methods of doing the same thing analog 
systems can do.


I actually find DSP detector systems inhibit my ability to hear or copy 
noise floor signals in rough noise. I'm not sure why that is, but it is more 
difficult for me to piece together a signal that is in the noise when it has 
been detected in a DSP system.


I normally set my K3's so DSP filtering is wider than the analog filter at 
filter switch in, so I can change the DSP bandwidth from wider than any 
analog filter down to the DSP being narrower, but I still think analog 
detection is much better for signals below the level of rough noise.


73 Tom 


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Re: Topband: alternative feedpoint capacitor

[Tom W8JI]

My top-loaded vertical needs a series 260pF capacitor at the feedpoint to
match the 53 + j335 impedance (1.825 MHz) to my coax feed.

I have a few different air-variables I could use, but I was wondering what
sort of fixed capacitors would be suitable in this application.

Max power is 1500w.  I have doorknob caps but they don't have current
ratings marked on them.



Steve,

You had some suggestions on capacitor types.

Finding the actual voltage and current on a series capacitor like this is 
pretty easy.


Voltage is the square root of the power times reactance. That is RMS, so you 
have to consider the peak plus a safety factor.  So you have the square root 
of 1500*335 or 708 volts RMS across the cap.


That's about 1kV peak. 2kV would give you good safety factor.

Current is just square root of the power over the load resistance.

sqrt of 1500/ 53   = 5.32 amps.

Exceeding voltage is an instant failure because it will arc. You want good 
headroom.


Current failures are heat and take a little time, so the heat averages over 
a short period of time. A physically large part can be somewhat abused in 
Ham duty for current.


73 Tom 


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Re: Topband: Fwd: Fwd: ARRL Board meets next week - I'm looking for input

[Tom W8JI]

I don't understand the sudden hysteria, except it may be Internet driven.

Around 52 years ago, my first or second 160 meter California contact was 
with remote W6YY. I can't remember if W6VSS Dale or W6YY was first, but that 
was when the band was split and the power limit was maybe 25 watts plate 
input power.


In the 1970's, when it was actually very difficult to work DXCC, W2EQS 
(Charlie) had almost made 100 DXCC on 160. His age and health forced him to 
move to Indiana, and he lost all of those credits.


Today (and for a long time now) anyone anywhere in the USA (remotely or 
locally) can operate anyone else's station in the USA under their call, or 
someone else can come in (remotely or physically) operate their station 
using the local call. People around here come in physically and operate my 
station, and they have for many years. It counts for their DXCC.


This leads me to think the sudden recent wave of hysteria about DXCC is 
based on people actually wanting one of three things:


1.) In spite of being legal for over 50 years, all remotes to be banned

2.) In spite of being legal for around 35 years that I know of, they want 
the rules changed so a station has to sign callsign / district or say 
portable and then district when transmitting from any location other than 
the station owner and builder location, and so no guest op can ever use his 
call. This is the way it was before the FCC changed that rule, which I think 
happened in the 1980's.


Since the FCC is unlikely to change rules because of an award that has not 
had that much meaning about being tied to any location, station, or operator 
since maybe 1980 or so, they want a new DXCC. They want a new DXCC that 
requires the contact to be made by the physical owner of the station at one 
location.


To me, the real issue is people are unhappy either with the use of a remote 
of any type (which has been legal as long as I have been a Ham and has been 
used for DXCC and contests since I have been licensed)  or they suddenly 
want DXCC to be tied to a station at a single location that the DXCC 
recipient owns.


I think the mob got all worked up because they didn't think about the actual 
rules, they just dislike RHR (and not the dozens of free uncontrolled 
remotes all over the place). For years they have been competing against 
people who use other people's stations, move around, or have a remote. Now, 
out of the clear blue sky, DXCC is suddenly useless when the actual changes 
than made it useless were made over 30 years ago.


I think the real solution is a DXCC endorsement or a new DXCC that requires 
the holder to swear he did it all transmitting and receiving from one 
location all by himself with gear he assembled. 


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Re: Topband: Video Switch for Low Band Antenna switching

[Tom W8JI]

BTW, besides having to rotate this switch only 22.5 degrees,it turns very
smoothly. I fiddled with the spring tension and lubed it for just the 
right

amount of torque without being sloppy.



In the 1970's, I started with a rotary switch, but didn't like it. I used 
push buttons from a telephone line switch. When the PB mechanical lock 
switches were wired with shielded wire, it worked good enough at least up 
through 40.


In the 1980's, I built a push button box with the buttons like a key pad. I 
hated it. I changed to in line buttons.


When we got seriously into contesting, I built boxes that buttons in a 
circle small enough to be worked with a thumb while resting a hand on the 
box, and a sloped front panel with no cabinet lip to get in the way. They 
have LED's by each button outside of the button circle so a thumb doesn't 
always block the lights.


The actual antenna group selection is on a rotary, which puts any array into 
any ear in stereo, and can lock a primary direction like NE or NW. These 
switches run a matrix that is all passive components, allowing any antenna 
into up to four output channels, and also allows the same antenna to be used 
by all output channels. This is an expandable matrix that could do 1, 2, 4, 
or 8 output channels and as many input ports as anyone wants within reason 
(maybe 30 or 40 is the limit).


I did this with strong push-pull low noise line amps, and it won't overload 
even with my own TX running. I don't (and won't) bridge across lines because 
of IMD and noise limitations. It is real quiet here in winter, so I have to 
be careful with dynamic range.


I have field relay boxes that allow up to two directions to be picked from 
any antenna hub at the same time and the NE antennas are available 
completely independent with as many receivers as anyone wants at the same 
time.


My boxes stay connected year in and year out, through thunderstorms and 
everything, and unless lightning actually hits an antenna (which has 
happened a few times in 15 years) they stay connected and working. 


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Re: Topband: A Bit Off Topic

[Tom W8JI]

Any suggestions appreciated on an effective electrical panel lightning
protection device for my panel breaker box.  Thanks and 73, Bob K3UL



Bob and all,

Keep in mind, spacing between conductors is typically very small compared to 
conductor length. Although there can be exceptions, virtually all damage is 
common mode that flows in parallel on bundles between things. (The same is 
generally true for RFI.)


The vast majority of protection comes from a common entrance ground bond, 
where everything entering a system, or everything entering an equipment hub, 
enters through one point where grounds are common bonded.


The most prolific damage, and the worse sensitivity to damage, occurs when 
widely separated things enter without being brought together at one point 
and bonded.


Broadcast sites go many years taking direct hits without damage without 
protection devices when they have proper entrance systems, while others are 
damaged by the weakest of external stimuli when they are improperly wired.


I have very few protection devices. I don't have an entrance panel ground, 
take dozens of strikes a year, never disconnect anything, and I never have 
problems. I've never lost a modem, even though the phone lines are above 
ground for miles. I have had wires outside melt from direct hits without 
inside equipment damage.


When stations have repetitious or severe damage, it is almost always a poor 
layout or poor wiring techniques. The best protection devices won't fix 
that.


73 Tom 


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Re: Topband: Binocular Cores

[Tom W8JI]

I'm with you up to this point, Tom, but here, you're mistaken. An 
effective common mode choke is dominantly resistive in the frequency range 
where it is to be used. The reactive component of the choke can be 
cancelled a length of feedline that is capacitive at the operating 
frequency, which increases the dissipation and makes the choke 
ineffective. The key to not having it fry is to make the Z high enough 
that the common mode current is small.



It works the way I said. I run into this ALL the time.  It is a constant 
headache for high power or high impedance circuits.


The choke has a certain equivalent parallel impedance.  The voltage across 
the resistive part of that impedance makes heat.  If we have a perfectly 
balanced load from a perfectly unbalanced source, the common mode voltage 
across the isolating choke is half of the voltage across the load terminals.


If we assume the load is 1000 ohms and power 1kW, voltage is P^2 over 1000 = 
1000 volts. In an ideal condition 500 volts would be across the isolation 
turn a simple choke represents.


If that choke is 10,000  j0, a very difficult task in the real worldat 
higher frequencies, we have 500 volts across 10k of resistance, or 25 watts 
dissipation. It is difficult to have enough CM resistance at high enough 
load impedances or voltages, even if the load is perfectly balanced.


(That is why ferrite core plate chokes are not in common use in amplifier 
with a few thousand volts or more.  We can't make impedance high enough to 
not cause too much core heat.)


Furthermore, the common mode circuit is NOT a simple voltage divider when 
the choke is added to the feedline of an antenna. Rather, it is part of an 
antenna system that includes the intentional antenna and the 
unintentional antenna (the feedline), and it is the lengths of those 
components, and the position of the choke, that will determine the voltage 
across the choke and the resulting current. To find the dissipation, we 
must add the equivalent circuit of the choke to an NEC model of the 
antenna with the choke and the feedline (as a single wire), including it's 
connection to ground. NEC will tell us the current in the choke, and I 
squared R is the dissipation. An antenna with severe imbalance can easily 
fry a very good choke at high power.


I certain agree there are many variables, but it is best to start with a 
simple model. Just to be clear, an antenna example with PERFECT balance can 
be a major issue with choke heating. This is why there is no such thing as a 
universal one thing fits all solution or one thing causes all the 
problems.  There are several things involved.


Because there are multiple variables working to create a wide range of end 
results, any discussion has to be clearly defined. I chose a simple ideal 
case of a perfectly unbalanced source feeding a perfectly balanced load of a 
certain resistive impedance and power.


This is an age old problem. It is a problem in higher voltage solid state 
amplifiers, as well as antenna baluns.


The worse answer to give people is it depends on many things, but that is 
often the only correct answer. One size will not fit all.


73 Tom 


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Re: Topband: Binocular Cores

[Tom W8JI]

That's good info, if you understand how to interpret it. It's not clear
what u' amd u are. And the info on their site doesn't tell you just how
good (low losses and reactance across a wide bandwidth, among other 
things)
a matching transformer is made from a 73 material binocular core. They 
only

offer it as RFI suppression.


Mike,

You might want to go to this page 
http://www.fair-rite.com/newfair/index.htm
and hover the link button [technical][Use of Ferrites in Broadband 
Transformers]


For receiving or low power transmitting, where voltage across a winding is 
minimal, you can use a core that presents a resistive impedance. That shunt 
impedance parallels the windings, so it has to be high compared to the 
operating impedance or the transformer will be lossy. Receiving or low power 
applications are very forgiving.


For high power, we get into trouble quickly. Since voltage across a winding 
can be fairly high, the parallel resistance has to be very high. Even then 
we can get into trouble. If a core dissipates just a few watts of heat it 
can go into thermal runaway, where it quickly reaches Curie temperature and 
no longer acts like a magnetic core.


Think about choke baluns where they have 10,000 ohms impedance, dominantly 
resistive. If you applied a 500 ohm load and 1000 watts you would have 2000 
V/2 =1000 volts in an ideal balance condition, which is 100 watts in the 
cores. This is why core selection generally has to shift to a dominantly 
reactive impedance, rather than resistive, at high power.


With a 100 watt lower voltage PA we might be able to use a  52 material. If 
it is higher voltage across the winding, the shunting resistance might kill 
it with heat. With high voltages across windings we might have to drop from 
a  52 material to 61, just to stop long term heating while maintaining the 
high end response.


What is simple and unimportant for low winding voltages really becomes a 
much more complex series of compromises at higher voltages across windings. 
That parallel resistance caused by the core is more problematic for heat 
than it is for loss.


73 Tom 


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Re: Topband: Topband loading coil

[Tom W8JI]

I have an inverted L antenna resonant on 80m, I decided to add a loading 
coil to the base to bring it on frequency for TopBand. I wound a 2.5mm wire 
coil 16 turns on a bit of square Paxoline board by drilling holes into the 
board each side and feeding the coil through the holes, a bit of a struggle 
but it worked, not very pretty, it is 146mm diameter and 120mm long 30.5uH. 
When I first tried it the SWR after small trimming was 1.2:1 band centre 
and 2.0:1 band edges. Now it looked a but ugly, so I decided to neat it up 
a bit by adding two fibreglass webs so the coil was now  circular and held 
by a cross section instead of just the one plane,  now when I retried the 
SWR it is still resonant on 1.800 but the SWR is now 2.0:1 in the middle of 
the band and 4.0:1 at the edges  the turns are the same, the inductance is 
the same but I have lost my fine SWR curve.






It sounds like when you neatened up the coil the Q increased, although 
perhaps something else changed.


If your earth losses are very low, the inductor Q can have a noticeable 
effect. The better the Q, the further from your goals of low SWR and wide 
bandwidth.


If you get the SWR lower in band center, the ends may come down.  You could 
put a shunt coil to ground across the feedpoint to do that.


73 Tom 


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Re: Topband: Binocular Cores

[Tom W8JI]

You really need to do a single loop through the core windows and measure the 
impedance with some sort of analyzer. Even an MFJ259B with a short 
connection to the jack will work well for this.


If the resistance equals the reactance down somewhere around 2 MHz, it is 73 
material.


If R=X someplace much higher, you can be sure it is a different mix. The Q=1 
frequency, where R=X or where loss tangent crosses reactance, tells you the 
material better than anything else you can do.


That is how I quickly sort unknown cores.

73 Tom




- Original Message - 
From: Roger Parsons via Topband topband@contesting.com

To: Topband topband@contesting.com
Sent: Monday, June 01, 2015 10:13 AM
Subject: Topband: Binocular Cores


I have some binocular cores which I know are FairRite mix 73. I have others 
which I thought were also mix 73. However, the first ones measure about 50k 
Ohms with ohmeter prods onto their surface, whereas the others only measure 
about 1k Ohm. I don't believe that that is a defined parameter, and am 
aware that the test is not very scientific, but I am surprised to see such 
a difference. Thoughts?

73 RogerVE3ZI
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-
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Topband: Unun and Balun on vertical

[Tom W8JI]

An UN-UN is un balanced to unbalanced. Is that what you have ? A vertical
is unbalanced.


It isn't that simple. Most Ham antennas are neither perfectly balanced nor 
perfectly unbalanced. They are somewhere between.


For example, a 1/4 wave groundplane with four perfect radials is mostly 
unbalanced, but still has considerable voltage between the radial center 
point and other things.


This is why, if we build a perfect 1/4 wave groundplane and do not use a 
choke balun or some other form of common mode decoupling, antenna SWR will 
go all over the place with coax or mast length.


By the time we get 15 or 20 (or maybe more) proper radials, it is almost 
perfectly unbalanced and common mode is not an issue, but less than that 
becomes an increasing problem.


I probably would not use an unun on a vertical unless the vertical had a 
pretty good ground, or unless I had a common mode choke of some type to 
decouple the feedline.


A current balun functions the same as a common mode choke. We just call it a 
balun, but it really is an isolator for common mode. It doesn't care, 
within its design limits, if the load is perfectly balanced, perfectly 
unbalanced, or someplace between. It might be labeled a balun, but it is 
directly interchangeable for an unun of the same ratio and has the 
additional feature of decoupling the feedline for common mode.


A voltage balun forces unbalanced voltages, and cannot be exchanged with an 
unun.  It has no common mode isolation, and will actually aggravate common 
mode problems on a vertical.


With a vertical with less than very good ground system and coax leaving 
below that ground, I would either use a current balun or some other form of 
common mode choke with matching. With a perfect system, I'd just use a form 
of L network or (reluctantly) an unun by itself.


73 Tom 


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Re: Topband: Antenna relays

[Tom W8JI]

With silver-cadmium relay contacts I use on my ladder line switching, I
find I have to occasionally transmit a dit to get receive to work again,
especially if I haven't been on the radio in hours or days. My mental 
model

is that I have to blow through the surface contamination. Would
definitely never use the silver-cadmium contacts in a receive-only path.
(Even though I have been known to make some Q's while transmitting on my
receive antennas, it was purely by accident!)


That's exactly what you are doing, blowing through a very thin surface 
contamination.


There are a few common forms of high resistance or open contacts. The very 
things that allow hot switching go contrary to receiving. For best results 
contact overlay has to be gold, it has to be cold switched (or switched with 
low voltage and current to not burn off the plating), and the contact needs 
to have a small surface area. Some relays are split into multiple small 
areas to increase contact area pressure and parallel areas.


The worse thing is a large area, because pressure across the area decreases 
for a given spring pressure.


A second issue, now more prevalent with everything being made offshore, are 
contaminants inside relays. The plastics can leech contaminants, or air 
sealed inside just might be dirty. This usually cures itself over time.


Low frequency performance, tests, and specs don't mean much. Skin effect 
seriously aggravates heating in some wires and contact current carriers. 


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