Re: Topband: Hi Gain Preamps, Noise Figure Comparison (KD9SV 994 x5, W1FB, W7IUV preamps)

[Bob K6UJ]

Don,

Thanks for sharing your research on the preamps.  Very informative.
Your study is very timely for me.
I have ordered DX Engineerings new phasing box, NCC-2.
Optional plug in preamps are available for the unit.  I am holding off
on ordering a preamp until I compare specs with other external preamps.
The KD9SV unit looks pretty good !
Now to find out how it compares.

Bob
K6UJ



On 11/8/16 1:54 PM, Don Kirk wrote:

Gary (KD9SV) kindly loaned me one of his 994 x5 preamps (sometimes called
KD9SV VLN (very low noise) preamp) so I could compare its Noise Figure
against one of my W1FB preamps as well as 2 of my W7IUV preamps in series
on 160 meters.

Here is a link to a youtube video I created that demonstrates the
differences in Noise Figure between the above mentioned preamps.
http://www.youtube.com/watch?v=JpIiF1Hfovw

The KD9SV 994 x5 preamp did in fact come out on top (best Noise Figure) and
it's a commercially available preamp, whereas my W1FB and W7IUV preamps are
home built.  Nevertheless in my current application (pennants that are
51.6% the size of full size pennants) the W1FB and W7IUV preamp Noise
Figures are adequate and I didn't notice improvement in my signal to noise
ratio on 160 meters when using the KD9SV preamp.  The lower Noise Figure of
the KD9SV would allow me to use even smaller pennant receive antennas that
would have more negative gain without harming my signal to noise ratio.

I ran into a couple of interesting issues when working on this project.
The biggest surprise was that the input impedance of my old HF rig (Kenwood
TS-180s) was no where near 50 ohms on 160 meters (it actually measured 189
ohms).  I added a transformer to the input of the Kenwood TS-180s to bring
it closer to 50 ohms for my testing.

Also as previously reported by Hardy (N7RT) a long time ago, the W1FB
output transformer turns ratio is incorrect for a 50 ohm match, and I
measured the output impedance of the W1FB preamp at 429 ohms.  I
subsequently added a transformer to the output to bring it closer to 50
ohms for my testing.

*Noise Figure Comparison (average of two different measurement methods)*
W1FB preamp: Noise Figure 3.3 dB higher than KD9SV 994 x5 preamp
Two W7IUV preamps in series: Noise Figure 1.1 dB higher than KD9SV 994 x5
preamp

Note 1: my W1FB preamp is not stock, as I made modifications to protect the
MC1350 IC from damage when transmitting.
Note 2: The KD9SV 994 x5 preamp was set at its maximum gain (41 dB) for all
of my tests.

*Summary*
While I suspect (through my measurements) that the KD9SV preamp absolute
Noise Figure value is not the very low 0.7 dB value listed on a commercial
website, it's indeed a very nice adjustable high gain preamp offering a
maximum gain of 41 dB and it has the best (lowest) Noise Figure when
compared with my other two types of preamps.  I highly recommend the KD9SV
994 x5 preamp if you're in need of a high gain preamp on 160 meters.

73,
Don Kirk (wd8dsb)
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Topband: ZD8W

[Joe Reisert]

Oliver, ZD8W asked me to post that he will be QRV on 1823.5 at 0400Z 
Wednesday morning his time.


GL and 73,

Joe, W1JR

--
Joe Reisert
Amherst, NH
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Re: Topband: Hi Gain Preamps, Noise Figure Comparison (KD9SV 994 x5, W1FB, W7IUV preamps)

[Don Kirk]

Hi JC,

I did not publish any absolute Noise Figure values, my measurements that I
published are all just differences in Noise Figure.

It actually is much easier to measure the difference in Noise Figure
between preamps that have such high gain (approximately 40dB in this case)
since the noise floor generated by a 50 ohm resistor at room temperature is
easily measurable (at least indirectly) after 40 dB of gain (It's -106.89
dBm for a 40 dB preamp using a bandwidth of 500 hertz if the preamp adds no
additional noise).  Even if you can't accurately measure -106.89 dBm level
signals, you just need to be able to be repeatable in your measurements
between preamps (accuracy and repeatability are not the same thing), and
your system must be able to detect differences in output signal from the
preamp in units of dB (easy to do with an SDR receiver at these levels
using attenuators to verify changes in dB on the SDR display).  In my case
all of my measurements were made with my Kenwood TS-180s operating on 160
meters, and then making measurements via the wideband IF output port of the
Kenwood TS-180s that's connected to an SDR receiver (the HDSDR software
also allowed me to do long term averaging, and it even allows you to
display power spectrum density).

My second method of measurement used the S meter on my TS-180s, but just as
an indicator (actually digitized the voltage supplied to the S meter).  I
recorded the signal strength on the S meter that the preamp generated when
the preamp input was terminated with the 50 ohm resistor, then I went back
and adjusted my signal generator connected directly to my TS-180s via
attenuators until it provided the same S meter reading.  Using the signal
generator and precision attenuators I was able to calculate the voltage
(and therefore power) into the TS-180s that the S meter recorded when
driven by the preamp.  I used this technique to compare Noise Figure
between preamps, and I made numerous measurements over a 6 day period and
then averaged the data to reduce my variation using this method.

I did in fact test the use of #31 mix cores (10 to 14 turns) on various
lines (power supply lines, 3 foot short feedline between preamp and
receiver input, etc. and saw no difference in signal levels.  I even
eliminated the Kenwood power supply, and fed the TS-180s with a lab grade
linear power supply to eliminate slight changes in supply voltage over time.

P.S. the Kenwood TS-180s is one of the better radios made in regards to
noise floor (measured -139 dBm by Sherwood).

It would certainly be much easier to make these measurements using a
spectrum analyzer, and I probably will acquire one of the lower cost Rigol
spectrum analyzers in the near future.  In the meantime I would love to
have someone independently make measurements comparing these amplifiers
that either supports or disproves my measured values.

73,
Don (wd8dsb)


On Tue, Nov 8, 2016 at 7:24 PM, JC  wrote:

> Hi Don
>
> Measuring noise figure below 1 db is a very complicated work.
>
> First you need to remove all common mode noise, your noise floor should be
> better than  -135 dBm at least with a 40 db preamp connected to the radio
> input and a 50 ohms load.
>
> You need chokes everywhere and most important shield on 12V, RF in and RF
> out. Check the AM band you hear carrier coming in , noise is also coming
> in.
>
>  Second the NF is very different on 1.8 MHz , measurement near 10 Mhz, does
> not tell you the right NF on low bands.
>
> In order to have Noise Figure Uncertainty near .2db it is necessary a good
> quality lab equipment, calibrated and two hours per measurement for each NF
> reading. This assuming the temperature does no change during the test.
>
>
> Your Noise Figure Uncertainty based on your video could be 5db or more.
>
>
> 73's
> JC
>
> N4IS
>
>
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Re: Topband: 160 m inverted L

[Grant Saviers]

Agree.  I use three fixed serial caps with shorting relays to tune my 
160m T, 8 elevated 125' radials, across the full band in 45KHz 
segments.  The antenna is cut for 1820 and fed with a 50::25 TLT.


The voltages across each cap (3 all the same value) is well below 400v 
at QRO so I used surplus 1Kv mica transmit caps from Ukraine. Small 
relays with 5Kv coil isolation short each cap.  SPST 12a DIP relays with 
very short duplex leads.  Never any hot switching so they are ok +4 years.


Interestingly the series cap values are all short, one=2000, two=1000, & 
three=667pf exactly move the needed for ~45KHz frequency, but other 
combinations might be necessary with other T's.  Use EZNEC!  I use a 
rotary switch with diode steering to select relay combos for each 
segment over a four wire cable.  I did shunt each cap with 100k ohms 2w 
carbon resistor to insure static charge was shared equally.


Cost about 10% of a vacuum variable and faster to move freq.  Not my 
idea, thanks to somebody on TB who suggested this - a winner.


Grant KZ1W

On 11/8/2016 15:12 PM, Herbert Schoenbohm wrote:
Bread slicers have their issues and are not really the best solution.  
Using a fixed high current mica G2 broadcast capacitor of a higher 
value than you need, and making it variable with a series inductor is 
the way to go.  This is what broadcast stations do in their ATU's.  I 
haven't ever seen a bread slicer in a radio station ATU.  A good high 
current mica cap and a flat wound taped coil IMHO is the way to make 
everything work well with no breakdowns.  For a wide range of matching 
consider a bridge T with fixed components and taped coils.  Go to 
W8JI's wonderful site for the values you need based on the impedance 
presented to your feed-line.




Herb, KV4FZ


On 11/8/2016 6:55 PM, Rob Atkinson wrote:

A vacuum variable for L impedance matching is unnecessary.  Vacuum
variable capacitors leak eventually.  It take a long time for them to
go through their ranges and you have to have the mechanics outside if
you perform remote tuning, to sense or count turns to track when the
v.v. is nearing its maximum or minimum.  It is far far easier and
faster to use an air variable that rotates freely.  You only need to
keep it sheltered.

Elevated radials are fine provided they are high enough to be
decoupled from earth, which for most hams is difficult to accomplish
on 160 m.

73

Rob
K5UJ
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Re: Topband: 160 m inverted L

[Bob K6UJ]

Makes sense Rob.
Probably a good approach is to find the capacitance needed and use
fixed vacuum caps in lieu of a vacuum variable.  Then we have a bullet
proof feed sys.  Fixed vac caps are plentiful on ebay.  I have collected
a bunch of them.
What height would be adequate for a 160 elevated radial to have decent 
decoupling ?
I think you are right, for most hams, including me, it is hard to get 
very much height

so we must compromise,  but we do the best that we can do.

Bob
K6UJ


On 11/8/16 2:55 PM, Rob Atkinson wrote:

A vacuum variable for L impedance matching is unnecessary.  Vacuum
variable capacitors leak eventually.  It take a long time for them to
go through their ranges and you have to have the mechanics outside if
you perform remote tuning, to sense or count turns to track when the
v.v. is nearing its maximum or minimum.  It is far far easier and
faster to use an air variable that rotates freely.  You only need to
keep it sheltered.

Elevated radials are fine provided they are high enough to be
decoupled from earth, which for most hams is difficult to accomplish
on 160 m.

73

Rob
K5UJ
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Re: Topband: Hi Gain Preamps, Noise Figure Comparison (KD9SV 994 x5, W1FB, W7IUV preamps)

[JC]

Hi Don

Measuring noise figure below 1 db is a very complicated work. 

First you need to remove all common mode noise, your noise floor should be
better than  -135 dBm at least with a 40 db preamp connected to the radio
input and a 50 ohms load.

You need chokes everywhere and most important shield on 12V, RF in and RF
out. Check the AM band you hear carrier coming in , noise is also coming in.

 Second the NF is very different on 1.8 MHz , measurement near 10 Mhz, does
not tell you the right NF on low bands.

In order to have Noise Figure Uncertainty near .2db it is necessary a good
quality lab equipment, calibrated and two hours per measurement for each NF
reading. This assuming the temperature does no change during the test.


Your Noise Figure Uncertainty based on your video could be 5db or more.


73's
JC

N4IS

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Re: Topband: 160 m inverted L

[Mike Waters]

I fully agree. And wide plate spacing isn't either, even at the legal limit!

I used an omega match (with two capacitors and no inductors) to match the
coax to my 160m inverted-L. The largest one in the photo on my site is
overkill, it's what I had.

73, Mike
www.w0btu.com

On Nov 8, 2016 4:55 PM, "Rob Atkinson"  wrote:
>
> A vacuum variable for L impedance matching is unnecessary.
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Re: Topband: 160 m inverted L

[Mike Smith VE9AA]

I’ve never owned a vacuum variable.  What I have been using for decades are
very large air variables hung from a stick, or tree or whatever and I cover
it up with a 2L pop bottle* with the bottom cut out of it.  Fix in place
with rope, string, tape, fishing line, whatever.

I can’t take credit for this trick (I don’t think anyways) as I have seen
hardline coax splices made much the same way many moons ago at the famous
VE1ZZ antenna farm.

It’s pretty rare for this to ever fail, or even have wx issues.  Of course
if you get screaming high winds with freezing rain going horizontal it is
possible to get a little frozen moisture up inside the bottle and then onto
the plates of the cap, but transmitting a few times usually solves the
problem.

 

*would  the equivalent of 2L pop bottle be ½ gallon soda bottle?

 

Mike VE9AA

 

 

A vacuum variable for L impedance matching is unnecessary.  Vacuum

variable capacitors leak eventually.  It take a long time for them to

go through their ranges and you have to have the mechanics outside if

you perform remote tuning, to sense or count turns to track when the

v.v. is nearing its maximum or minimum.  It is far far easier and

faster to use an air variable that rotates freely.  You only need to

keep it sheltered.

 

Elevated radials are fine provided they are high enough to be

decoupled from earth, which for most hams is difficult to accomplish

on 160 m.

 

73

 

Rob

K5UJ

 

Mike, Coreen & Corey

Keswick Ridge, NB

 

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Re: Topband: 160 m inverted L

[HAROLD SMITH JR]

  From: Herbert Schoenbohm 
 To: topband@contesting.com 
 Sent: Tuesday, November 8, 2016 5:12 PM
 Subject: Re: Topband: 160 m inverted L
   
Bread slicers have their issues and are not really the best solution.  



Herb, I must agree with you. Over 25 years ago, I tried to shunt feed my tower. 
I had a very heavy duty "bread-slicer".It tuned fine. But when I put power, 
1500 watts, to it the plates warped. I changed to a couple of Vacuum Variables, 
500pF @ 7.5kV and everything is fine. The tuning has never changed. I set it to 
1830kHz @ 1:1 vswr and the 2:1 bandwidth is ~ 40kHz. 73 de Price W0RI












   
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Re: Topband: 160 m inverted L

[Herbert Schoenbohm]

Bread slicers have their issues and are not really the best solution.  
Using a fixed high current mica G2 broadcast capacitor of a higher value 
than you need, and making it variable with a series inductor is the way 
to go.  This is what broadcast stations do in their ATU's.  I haven't 
ever seen a bread slicer in a radio station ATU.  A good high current 
mica cap and a flat wound taped coil IMHO is the way to make everything 
work well with no breakdowns.  For a wide range of matching consider a 
bridge T with fixed components and taped coils.  Go to W8JI's wonderful 
site for the values you need based on the impedance presented to your 
feed-line.




Herb, KV4FZ


On 11/8/2016 6:55 PM, Rob Atkinson wrote:

A vacuum variable for L impedance matching is unnecessary.  Vacuum
variable capacitors leak eventually.  It take a long time for them to
go through their ranges and you have to have the mechanics outside if
you perform remote tuning, to sense or count turns to track when the
v.v. is nearing its maximum or minimum.  It is far far easier and
faster to use an air variable that rotates freely.  You only need to
keep it sheltered.

Elevated radials are fine provided they are high enough to be
decoupled from earth, which for most hams is difficult to accomplish
on 160 m.

73

Rob
K5UJ
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Re: Topband: 160 m inverted L

[Rob Atkinson]

A vacuum variable for L impedance matching is unnecessary.  Vacuum
variable capacitors leak eventually.  It take a long time for them to
go through their ranges and you have to have the mechanics outside if
you perform remote tuning, to sense or count turns to track when the
v.v. is nearing its maximum or minimum.  It is far far easier and
faster to use an air variable that rotates freely.  You only need to
keep it sheltered.

Elevated radials are fine provided they are high enough to be
decoupled from earth, which for most hams is difficult to accomplish
on 160 m.

73

Rob
K5UJ
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Topband: Hi Gain Preamps, Noise Figure Comparison (KD9SV 994 x5, W1FB, W7IUV preamps)

[Don Kirk]

Gary (KD9SV) kindly loaned me one of his 994 x5 preamps (sometimes called
KD9SV VLN (very low noise) preamp) so I could compare its Noise Figure
against one of my W1FB preamps as well as 2 of my W7IUV preamps in series
on 160 meters.

Here is a link to a youtube video I created that demonstrates the
differences in Noise Figure between the above mentioned preamps.
http://www.youtube.com/watch?v=JpIiF1Hfovw

The KD9SV 994 x5 preamp did in fact come out on top (best Noise Figure) and
it's a commercially available preamp, whereas my W1FB and W7IUV preamps are
home built.  Nevertheless in my current application (pennants that are
51.6% the size of full size pennants) the W1FB and W7IUV preamp Noise
Figures are adequate and I didn't notice improvement in my signal to noise
ratio on 160 meters when using the KD9SV preamp.  The lower Noise Figure of
the KD9SV would allow me to use even smaller pennant receive antennas that
would have more negative gain without harming my signal to noise ratio.

I ran into a couple of interesting issues when working on this project.
The biggest surprise was that the input impedance of my old HF rig (Kenwood
TS-180s) was no where near 50 ohms on 160 meters (it actually measured 189
ohms).  I added a transformer to the input of the Kenwood TS-180s to bring
it closer to 50 ohms for my testing.

Also as previously reported by Hardy (N7RT) a long time ago, the W1FB
output transformer turns ratio is incorrect for a 50 ohm match, and I
measured the output impedance of the W1FB preamp at 429 ohms.  I
subsequently added a transformer to the output to bring it closer to 50
ohms for my testing.

*Noise Figure Comparison (average of two different measurement methods)*
W1FB preamp: Noise Figure 3.3 dB higher than KD9SV 994 x5 preamp
Two W7IUV preamps in series: Noise Figure 1.1 dB higher than KD9SV 994 x5
preamp

Note 1: my W1FB preamp is not stock, as I made modifications to protect the
MC1350 IC from damage when transmitting.
Note 2: The KD9SV 994 x5 preamp was set at its maximum gain (41 dB) for all
of my tests.

*Summary*
While I suspect (through my measurements) that the KD9SV preamp absolute
Noise Figure value is not the very low 0.7 dB value listed on a commercial
website, it's indeed a very nice adjustable high gain preamp offering a
maximum gain of 41 dB and it has the best (lowest) Noise Figure when
compared with my other two types of preamps.  I highly recommend the KD9SV
994 x5 preamp if you're in need of a high gain preamp on 160 meters.

73,
Don Kirk (wd8dsb)
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Topband: BOIG antenna changes

[K1FZ-Bruce]

Years ago, before 1920, Harold Beverage ran a "wave antenna" wire on the ground 
on Mount Desert Island, Maine over the rocks on the shore line to a Navy 
Barrage receiver, near Otter Cliff's.  He discovered its directional 
properties. 
Later about  ca ~1948 Albert E. Weymouth, Original W1BX call sign, had me, a 9 
year neighbor kid, help him with a wire on ground, and also with a buried  
under ground wire antenna.  
I bring this up because I recently heard someone on 160 SSB  give a, now middle 
age ham, credit for inventing the BOG antenna. 
 
Many times I have inquires from those new to 160 meters and interested in a BOG 
antennas.  With Beverage as part of the name Multi band operation is assumed. 
Research by Luis, IV3PRK at HC1PF has confirmed that the antenna is a one band 
device when expecting a real good pattern. Reduced directivity can be found on 
other bands

Please check out both of  Luis WEB pages:
http://www.iv3prk.it/new-page.htm
http://www.iv3prk.it/bog-modeling.htm
 
 A name change  has been talked about, but never got going. 
Wire on ground is most descriptive, with WOG a single letter change. 

 
Started the ball rolling (slowly) by changing the bogantennanotes wording, and 
will continue  as time permits.. 
http://www.qsl.net/k1fz/bogantennanotes/
 
 
73
Bruce-K1FZ  
  

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Re: Topband: Fw: 160 m inverted L

[Guy Olinger K2AV]

The business of avoiding high angle radiation at all costs is a real urban
myth on 160. NVIS closing of close-in skip zones on 160 can save your run
frequency in contests.

While creating an R=50, X= whatever feed Z is certainly useful, other
issues are paramount. Reduction of current in the counterpoise is always a
reduction in ground losses. For situations where the loss is unavoidably
high, going beyond R=50 may be worth it for efficiency reasons.

There is also the significantly erroneous myth that high angle radiation
from an L is taken away from the low angles. Some time in modeling shows
that higher efficiency provides the difference. The low angle radiation
remains fairly constant and simply depends on the height of the vertical
wire and the shape of the RF current density on the vertical wire.

There is also the myth that high angle makes RX worse. Being plain jane
vertical in part is what makes RX worse. To that end, to really hear on
160, one uses RX antennas to hear. In that case, who cares to what degree a
TX antenna hears. You can't fix the TX antenna's problem that it is a large
vertical antenna that will hear all the local vertically polarized noise.
The fix is to use various RX antennas. So who cares about TX antennas' RX.
If you are serious, you will get RX antennas. Many different RX antenna
solutions, workable, effective, beats RX-on-TX-antenna to a bloody pulp.

Then there is the business of a long horizontal wire moving the current
density up to fill out the entire vertical run, and getting more RF out at
low angles over the local RF-lossy ground clutter.

It is convenient that an emerging efficient range of an L's Hor + Vert wire
= 140-155 feet, does conveniently and decently meet other goals.

If you are doing QRP or 100W in a contest, filling in the skip zones caused
by pure vertical antennas will help you do running instead of all S, and
significantly improve your score, and yes, I meant running instead of all
S while QRP on 160m.

73, Guy K2AV

On Tue, Nov 8, 2016 at 12:34 PM, Charles Moizeau  wrote:

> From: Charles Moizeau 
> Sent: Tuesday, November 8, 2016 12:32 PM
> To: farr...@yahoo.com
> Subject: Re: Topband: 160 m inverted L
>
>
> An advantage of having the total length of the inverted L antenna at
> greater than 0.25 wavelength is that matching to coax at its base can be
> achieved with just a capacitor in series between the center conductor and
> the antenna.  No lossy inductors are present.  Also, a costly vacuum
> variable capacitor overcomes losses in the capacitor rotor's thrust
> bearing.  (The same benefit can be more cheaply obtained by bridging the
> thrust bearing with a piece of braided solder wick, or using a split-stator
> or butterfly capacitor with its rotor left floating, though finding such a
> capacitor with enough capacitance for 160m can be difficult).
>
>
> Assuming 128 feet to be the equivalent of 0.25 wl on 160m, John's
> arrangement puts the current maximum at 128 point back from the L's open
> end.  This is true for all antennas having a total length greater than 0.25
> wl.  And in John's case the current maximum occurs at  a point that is 17
> feet up from its base.
>
>
> For low-angle radiation, arranging the L's total length to concentrate a
> maximum of current in the vertical leg requires the maximum current point
> to be situated at the midpoint of the vertical leg.  Look at figure 2.5 in
> Moxon's worthy book to see this nicely illustrated.  In John's case a
> horizontal leg of 95.5 feet would achieve this.
>
>
> However, there are disadvantages of such an arrangement.
>
>
> First, a longer horizontal leg will attract more high-angle signals while
> receiving.  This can be eliminated by making the antenna a vertical Tee
> with two legs, each 95.5 feet long and faced 180 degrees apart, and this
> will also cancel high-angle transmitted radiation.
>
>
> Second, if you accept the premise that the function of radials, in this
> case assuming radials lain on the ground, is to collect radiation from the
> vertical leg that splashes off the ground and return it to the feedpoint
> for "recycling", then moving the antenna's maximum current point up to the
> vertical leg's midpoint will have the radiation splashing further away from
> the antenna base than would occur with a maximum current point at 17 feet
> high, as with John's present antenna.  Obviously the higher in the vertical
> leg the maximum current occurs, then longer radials will be required for
> greater collection effect.  Even at a 17-foot height radials should be
> longer than they would be with a total antenna length of 128 feet, with its
> maximum current point at ground zero.
>
>
> 73,
>
>
> Charles, W2SH
>
>
>
> From: Topband  on behalf of John Farrer
> via Topband 
> Sent: Tuesday, November 8, 2016 2:43 AM
> To: Wes Attaway (N5WA)
> Cc: topband@contesting.com; Art Heft
> Subject: Re: Topband: 160 

Re: Topband: 160 m inverted L

[Mike Waters]

On Tue, Nov 8, 2016 at 12:23 PM, Rob Atkinson  wrote:

> I have no idea what a "FCP" is, but it doesn't matter.
>
> 1.  An inverted L is an _unbalanced_ antenna.  Therefore you don't need a
> balun.
>

An FCP is a Folded Counterpoise. Basically, it's an elevated radial for
160m ops without room for a proper radial system.
http://lists.contesting.com/_topband/2012-07/msg00413.html

And we can use FAR fewer radials if we elevate them.
lists.contesting.com/_topband/2007-11/msg00248.html

And elevated radials require a good common-mode choke. This page links to
what I used, though K9YC's design called for another core and another turn
or two.
www.w0btu.com/160_meters.html#inv-l_antenna

73, Mike
www.w0btu.com
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Re: Topband: 160 m inverted L

[Rob Atkinson]

I have no idea what a "FCP" is, but it doesn't matter.

1.  An inverted L is an _unbalanced_ antenna.  Therefore you don't
need a balun.
2.  This means you can feed it with unbalanced line, i.e. coax.
3.  You can use an unbalanced matching network such as an L network,
preferably at the feedpoint.
4.  Make the total length of the driven element around 140 feet and
put down enough radials, 60 to 100 is good, and you have no problems
with common mode RF on the feedline.  The returning current to the
feedpoint is distributed over enough conductors so that what's on the
feedline is minuscule.  If you have to fool around with ferrite cores
and such then you don't have enough radials down.

73

Rob
K5UJ
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Re: Topband: Fw: 160 m inverted L

[Bob K6UJ]

Charles,

Thanks for the very informative post !
I am planning an install of a 160M inv L myself and appreciate the info.


Bob
K6UJ


On 11/8/16 9:34 AM, Charles Moizeau wrote:

From: Charles Moizeau 
Sent: Tuesday, November 8, 2016 12:32 PM
To: farr...@yahoo.com
Subject: Re: Topband: 160 m inverted L


An advantage of having the total length of the inverted L antenna at greater 
than 0.25 wavelength is that matching to coax at its base can be achieved with 
just a capacitor in series between the center conductor and the antenna.  No 
lossy inductors are present.  Also, a costly vacuum variable capacitor 
overcomes losses in the capacitor rotor's thrust bearing.  (The same benefit 
can be more cheaply obtained by bridging the thrust bearing with a piece of 
braided solder wick, or using a split-stator or butterfly capacitor with its 
rotor left floating, though finding such a capacitor with enough capacitance 
for 160m can be difficult).


Assuming 128 feet to be the equivalent of 0.25 wl on 160m, John's arrangement 
puts the current maximum at 128 point back from the L's open end.  This is true 
for all antennas having a total length greater than 0.25 wl.  And in John's 
case the current maximum occurs at  a point that is 17 feet up from its base.


For low-angle radiation, arranging the L's total length to concentrate a 
maximum of current in the vertical leg requires the maximum current point to be 
situated at the midpoint of the vertical leg.  Look at figure 2.5 in Moxon's 
worthy book to see this nicely illustrated.  In John's case a horizontal leg of 
95.5 feet would achieve this.


However, there are disadvantages of such an arrangement.


First, a longer horizontal leg will attract more high-angle signals while 
receiving.  This can be eliminated by making the antenna a vertical Tee with 
two legs, each 95.5 feet long and faced 180 degrees apart, and this will also 
cancel high-angle transmitted radiation.


Second, if you accept the premise that the function of radials, in this case assuming 
radials lain on the ground, is to collect radiation from the vertical leg that splashes 
off the ground and return it to the feedpoint for "recycling", then moving the 
antenna's maximum current point up to the vertical leg's midpoint will have the radiation 
splashing further away from the antenna base than would occur with a maximum current 
point at 17 feet high, as with John's present antenna.  Obviously the higher in the 
vertical leg the maximum current occurs, then longer radials will be required for greater 
collection effect.  Even at a 17-foot height radials should be longer than they would be 
with a total antenna length of 128 feet, with its maximum current point at ground zero.


73,


Charles, W2SH



From: Topband  on behalf of John Farrer via Topband 

Sent: Tuesday, November 8, 2016 2:43 AM
To: Wes Attaway (N5WA)
Cc: topband@contesting.com; Art Heft
Subject: Re: Topband: 160 m inverted L

FWIW mine is cut  by trial and error to 1825 and is approximately 65 feet 
vertical and 80 feet horizontal. I have moved it around to three different 
locations over the last 2 years. The dimensions change very little, perhaps 2 
feet. The SWR can be tweaked by raising or lowering the FCP a little.

Good luck
John G3XHZ


Sent from my iPhone


On 8 Nov 2016, at 03:23, Wes Attaway (N5WA)  wrote:

I haven't run any numbers but it seems like you should just shorten the
horizontal wire (resonance freq is too low).  I would go back to about 65'
horizontal.  Somewhere in the range of 60' to 70' you should get close
enough.

   ---
Wes Attaway (N5WA)
(318) 393-3289 - Shreveport, LA
Computer/Cellphone Forensics
AttawayForensics.com
   ---

-Original Message-
From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Art Heft
Sent: Monday, November 07, 2016 3:06 PM
To: topband@contesting.com
Subject: Topband: 160 m inverted L

I finally got the inverted L up this afternoon.  Vertical dimension is 65'
and the almost horizontal dimension is 95'.  I am using a very carefully
built FCP and the commercial transformer.  My SARK 110 shows resonance at
about 1.68 MHz but the resistive part is up around 1000 ohms.  Taken right
at the antenna.  Doesn't seem right to me.  Any ideas?
73, Art K8CIT Hillman MI
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