Re: Topband: Loop on the ground as a counterpoise

[shristov]

The usual kind of field produces radial currents,
and that's why we use radial wires.

But what kind of field would make the current run in circles?

Or is it that the only effective piece of wire is the radial one,
connecting the loop to the coax shield?

Perhaps we need a clear understanding of this?


73,

Sinisa  YT1NT, VE3EA

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

Re: Topband: Broadside Beverages and Diversity observations

[shristov]

VE6WZ_Steve  wrote:

> most noise is equally distributed in all AZ directions


In such a case the level of received noise does not depend
on antenna directivity.

This follows from the fact that all antennas have the same
average directivity, i.e.  0 dB


73,

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

Re: Topband: Fresnel Zone

[shristov]

> donov...@starpower.net wrote:

> The classic source for Fresnel zones as they apply to HF site
> selection is NBS Technical Note 139:
> https://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote139.pdf


This indeed is a classical source, but it should be noted that the derivation
assumes that the elevation angle actually used for communication
is equal to the elevation angle of the peak of lowest ground reflection lobe.

This may or may not be the case.

In amateur operation, communication is often done using elevation angles
well below the peak of the lowest lobe, because of inability to erect very high 
antennas.
In such cases, the first Fresnel zones extends much further than the
equation 3.4-4 predicts. Correct formulas may be derived using the same
procedure, while separating communication angle from lobe peak angle.

Using vertical antennas additionally complicates matters.
I am not aware of any work on this topic.


73,

Sinisa  YT1NT, VE3EA



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

Re: Topband: comparison of SNR of two antennas with 2 channel SDR and Linrad

[shristov]

> a shortvideo on comparison of SNR of two antennas with two
> channel SDR and Linradsoftware may be found here:

https://www.youtube.com/watch?v=UzP03mZVLvE

Perfectly done and very informative.
Thank you, Piotr!


73, Sinisa YT1NT


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

Re: Topband: FT-1000MP

[shristov]

> do not know who Receiver Front-End RF Amplifier should be active
> for optimal performance for 160 m.  I have a choice of flat 
> or Tuned for low band.

When you receive on normal (TX) antenna,
use:  PREAMP=NONE (IPO green LED ON),   ATTN=18 dB (max).

Whenever the background noise make the S meter move,
there is too much gain.


73,

Sinisa  YT1NT, VE3EA
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: The band sans noise

[shristov]

JC  wrote:

> http://wwrof.org/wp-content/uploads/2016/03/WWROF-WEBNAIR-RX-Antennas-for-a-Small-Lot-.pdf


The file starts with some incorrect statements:

   "All we need is 3 dB SNR for CW and 8 dB for SSB"

   such a statement is completely meaningless if the measurement bandwidth is 
not stated
   "3 dB SNR" with BW=3000 Hz becomes 18 dB SNR with BW=100 Hz,
   with readability practically unchanged


  "Signal 30db above noise"  (pointing to the spectrum diagram)

  This is comparing apples to oranges.
  The difference depends on the measurement bandwidth, as above,
  so "30 dB" is meaningless if the measurement bandwidth is not stated


73,

Sinisa  YT1NT, VE3EA
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Handheld Impedance Analyzer

[shristov]

 "Richard (Rick) Karlquist"  wrote:

> I don't believe the above assertion.
 
> Can anyone give a specific example of an antenna having
> an SWR at the resonant frequency, (where X=0), that is higher than
> the SWR at frequencies slightly above or below the resonant frequency?
 
> I submit that a local minimum in the SWR will always coincide
> with X=0.  This is easily proved on a Smith chart, where X=0
> corresponds to the X-axis.  Adding reactance or susceptance moves
> the impedance farther from the origin in all cases, meaning SWR goes up.


It would be exactly so if the real part of the antenna
input impedance did not change with frequency.

The real part of dipole impedance rises quite a bit with frequency, so the 
resonant
frequency as defined by X=0 will be different from the minimum SWR frequency.
With multi-element beams, R may change with frequency in more complex ways.

But for a given coax impedance, what should be aimed for is the lowest
maximum SWR in the working frequency range (subject to preferences).
The resonant frequency itself, defined as X=0 or otherwise, is irrelevant.

73,

Sinisa  YT1NT, VE3EA







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

Re: Topband: WEB address correction: : RDF in the real-world

[shristov]

"K1FZ-Bruce"  wrote:

> IV3PRK at HC1PF with the help of friends proved with extensive research and 
> modeling,
> that a BOG antenna is a tuned circuit not a traveling wave antenna.

BOG is a traveling wave (Beverage) antenna at its best.

If some "tunning" artefacts were present,
they probably resulted from incorrect termination,
varying height above ground, and varying ground properties.

Those "tunning" artefacts by no means negate the traveling wave principle,
although an additional (interfering) voltage may appear.

73,

Sinisa  YT1NT, VE3EA


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

Re: Topband: WEB address correction: : RDF in the real-world

[shristov]

donov...@starpower.net wrote:

> The correct URL is: 
> www.qsl.net/k1fz/bogantennanotes.html 

>From that page:
  Because the BOG is "trying" to develop signal voltage between the wire and 
the earth it sits upon

This is misleading at best.

The voltage results from the current flowing in the BOG wire.
The voltage can be produced without any earth connection,
e.g. if lossless short symmetrical counterpose was used.

73,

Sinisa YT1NT, VE3EA
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Placement of RX feedline chokes

[shristov]

Herbert Schoenbohm  wrote:

> where is the best placement for for a feed-line choke?


At each point where the common to differential mode conversion is likely to 
happen.
In other words, where the current on the outside of coax shield is likely to 
get inside coax.

Primary target points are those where the coax [potentially] opens to the outer 
world:
antenna end, station end, coax extension joints, and similar.

In addition, placing several chokes at lambda/4 distance from each other
will make it difficult to develop large coax shield currents in the first place.


73,

Sinisa  YT1NT, VE3EA

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

Re: Topband: ADC Overload from MW transmitters

[shristov]

Rudy Bakalov via Topband  wrote:

> This is not true - higher sample rates are just as effective in 
> reducing overload as higher bit resolution.
...
> The higher sample rates reduces the probability of multiple signals 
> happening at the same time and overloading the ADC.


A higher sample rate alone
will not change the probability of overloading the ADC.
The percentage of meaningless samples will stay the same,
and consequences of overloading will not change.

A higher sample rate will help only if:
  a) it results in a higher equivalent bit resolution, and
  b) the input full-scale range is increased so to keep the equivalent LSB 
value at the previous level.


73,

Sinisa YT1NT, VE3EA
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Commond mode choke for Beverage

[shristov]

If you must use FT240-61, then in a single layer about 18 turns of RG58 would 
fit,
which should give you ~600 Ohms on 1.8 MHz. That would be very good for a 
dipole,
but for a Beverage a much higher impedance is needed. Try to fit as many turns
as possible, until there is no more room in the center of the core.

Alternatively, use RG174. In a single layer you should be able to put ~32 turns,
which will give you a respectable 2000 Ohms on 1.8 MHz.  But in this case take 
care
to make all coax joints (RG174 to RG58) completely shielded, eg. by using a 
copper foil.

73,

Sinisa  YT1NT, VE3EA



- Originalna poruka -
Pošiljalac: JC 
Datum: Ponedeljak, Oktobar 12, 2015 15:40
Tema: Re: Topband: Commond mode choke for Beverage
Primalac: 'Filipe Lopes' , 'topBand' 

> Hi Filipe
> 
> Zero , you should use material #31  or #77 , The core you 
> have is not good
> for low bands.
> 
> JC
> N4IS
> -Original Message-
> From: Topband [mailto:topband-boun...@contesting.com] On Behalf 
> Of Filipe
> Lopes
> Sent: Monday, October 12, 2015 8:46 AM
> To: topBand 
> Subject: Topband: Commond mode choke for Beverage
> 
> Hi guys,
> 
> I am about to add a common mode choke to isolate the antenna 
> from its
> feedline to each of my beverages and I only have FT240-61 
> ferrites. My
> question is how many turns should I do on the ferrite using RG58 
> (all my
> bevs are fed with RG58). Also should I put the choke near the 
> 9:1 balun or
> near my bev switching box?
> 
> Thanks in advance.
> 
> 73's Filipe Lopes
> CT1ILT - CR6K
> F4VPX - TM3M
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
> 
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Commond mode choke for Beverage

[shristov]

With 5943003801 and RG58, closely fill-in a single layer,
leaving 10-15 mm on the outside perimeter unused.
That should be ~16 turns, giving you impedance near 4000 Ohm.

Such a choke should be placed close to all points where
the current on the outer surface of the coax shield
can pass to the coax inside space.

This usually means near RX connector, and at the Beverage end of the feeding 
coax.
If the feed line is very long, then a few chokes may be inserted here and there.

But take care to make all coax joints completely shielded,
otherwise chokes may be bypassed.


73,

Sinisa  YT1NT,  VE3EA



- Originalna poruka -
Pošiljalac: Filipe Lopes 
Datum: Ponedeljak, Oktobar 12, 2015 15:52
Tema: Re: Topband: Commond mode choke for Beverage
Primalac: JC 
Cc: topBand 

> Hello JC,
> 
> Thanks for your answer.
> 
> I just ordered a few 2631803802 and 5943003801 from mouser.
> 
> With these ferrites I ask the same question, should I put the 
> choke close
> to the 9:1 Balun or near the switching box and how many turns? 
> some bevs
> have the feed point at +- 60m away from the switching box.
> 
> 
> 73's Filipe Lopes
> CT1ILT - CR6K
> F4VPX - TM3M
> 
> 2015-10-12 15:40 GMT+02:00 JC :
> 
> > Hi Filipe
> >
> > Zero , you should use material #31  or #77 , The core you 
> have is not good
> > for low bands.
> >
> > JC
> > N4IS
> > -Original Message-
> > From: Topband [mailto:topband-boun...@contesting.com] On 
> Behalf Of Filipe
> > Lopes
> > Sent: Monday, October 12, 2015 8:46 AM
> > To: topBand 
> > Subject: Topband: Commond mode choke for Beverage
> >
> > Hi guys,
> >
> > I am about to add a common mode choke to isolate the antenna 
> from its
> > feedline to each of my beverages and I only have FT240-61 
> ferrites. My
> > question is how many turns should I do on the ferrite using 
> RG58 (all my
> > bevs are fed with RG58). Also should I put the choke near the 
> 9:1 balun or
> > near my bev switching box?
> >
> > Thanks in advance.
> >
> > 73's Filipe Lopes
> > CT1ILT - CR6K
> > F4VPX - TM3M
> > _
> > Topband Reflector Archives - http://www.contesting.com/_topband
> >
> >
> _
> Topband Reflector Archives - http://www.contesting.com/_topband
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Commond mode choke for Beverage

[shristov]

 Eduardo Araujo via Topband  wrote:

> My two cents..It was interesting during the installation of 
> the last beverage, we have only #31 core, so we placed it at the 
> receiver side. Disconnecting the coax at the bev feed point and 
> shorting the coax there, many AM broadcast stations could be 
> heard and some of them strong, indicating that even though one 
> choke was at the receiver side the coax was acting like an 
> antenna. The coax was just lying on the ground and is 40/50 mts 
> long. 

> When we got more cores and placed one choke at that place close 
> to the short, repeating the test before and after most broadcast 
> vanished and only one could be heard very week.


This is exactly as expected.

In the first case you fed all the RF received by the outer surface of the coax
directly inside the coax, and directly to your RX input.

In the second case, a significant isolating impedance was added
and the said RF was attenuated.

73,

Sinisa  YT1NT, VE3EA
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: vertical balun

[shristov]

Bob Kupps wrote:

 Right now we are feeding it through a 4:1 balun (not a unun) with 12.5 ohms 
 on the 
 balanced side, and the SWR is 1.4 with no matching network.


You should get quite a reasonable SWR with no matching at all.
A good high-impedance common mode choke is recommended.

73,

Sinisa  YT1NT, VE3EA
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Modeling Ground and losses

[shristov]

Tom W8JI w...@w8ji.com wrote:

  Of interest here is that the benchmark Brown, Lewis and Epstein I.R.E 
  paper on ground systems does not show such standing waves along buried 
  radials (clip below).

 Of interest down here is surface-buried radials down here show definite 
 standing waves in actual measurements, so it doesn't care what BL and E 
 measured.


Their Fig. 7 shows results of simplified (manual) calculations, not measurement 
results.


73,

Sinisa  YT1NT, VE3EA
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Modeling Ground and losses

[shristov]

Richard Fry r...@adams.net  wrote:

 Quoting from page 771 of the BLE paper on ground systems:
 
 The current in the buried wires was measured in each case.

That quote does not apply to Fig. 7, which is 10 pages earlier.

This quote from p. 760 applies to Fig. 7:

...the following calculations are made on this basis. The current in the wires 
is shown... :
   Fig. 7  ...
   Fig. 8 ...
   Fig. 9 ...
   Fig. 10 ...


73,

Sinisa


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

Re: Topband: Modeling Ground

[shristov]

Guy Olinger K2AV k2av@gmail.com wrote:

 Sommerfeld and all the rest are tuned APPROXIMATION algorithms
 that seem well-calibrated only in the commercial BC paradigm.

Sommerfeld integral is not an approximation, has not been tuned,
and has no provision for tuning.

Sommerfeld integral is an exact solution of Maxwell equations
for the case of infinite, plane and homogenous ground.

Of course, our actual grounds are neither infinite, nor plane,
and they are certainly not homogenous, but that's another story.

Caution and common sense must be exercised with
Sommerfeld method, or any other theoretical method.
With due attention payed, something can always be gained
from sound theoretical calculations, but they must not be
consumed with a blind faith.

73,

Sinisa  YT1NT, VE3EA
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Modeling Ground

[shristov]

Guy Olinger K2AV k2av@gmail.com wrote:

 And yes it IS tuned, read the program code.

This is interesting.  Where in those 10,000+ lines is the tuning hack?


73,

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

Re: Topband: TX relays

[shristov]

Mike Waters mikew...@gmail.com wrote:

 I just popped the cover off a little Omron PCB-mounting relay that I forgot
 I had, rated at 10 kV.


10 kV between contacts, or 10 kV between a contact and the coil?


73,

Sinisa  YT1NT, VE3EA

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

Re: Topband: 160M loading coil mounting/orientation

[shristov]

rich kennedy via Topband topband@contesting.com wrote:

 When base-mounting a loading coil (inductor) on a shortened 
 monopole vertical, is there a preferred method for the physical 
 placement of the coil?  Is it better to orient the coil in 
 the vertical axis, horizontal axis; very close to the radiator 
 element or a number of feet away; positioned close to ground 
 level or elevated (such as on a mounting post ~ 3 feet above ground)?
 Assume freq = 1.83 mHz; H = 70 feet aluminum; soil = average to 
 good; small capacitive hat (spokes, 5’ diameter). 

Orientation doesn't matter.

Place it as you would place any other inductor,
i.e. 1-2 coil diameters away from other metallic objects, and from soil.

Protect it from elements, and that's it.

73,

Sinisa  YT1NT, VE3EA
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Ferrites and verticals

[shristov]

Henk PA5KT pa...@remijn.net  wrote:

 Is a choke needed, and where do I place it on a regular 1/4 
 vertical and where on a HF[6|9]V?

The purpose of a choke is to prevent the coax shield
from becoming a part of your antenna.

Do you want to connect directly to your antenna
a long conductor with random length and position,
connected directly to your household appliances and
to other innumerable sources of noise?'

If not, place a good enough choke at antenna feed terminals.
Additional chokes may have to be placed elsewhere, but that's another story.

What constitues a good enough choke depends on circumstances.
In general, a choke with common mode impedance of at least 500 Ohm
is required for well behaved antennas such as symmetrical dipoles and beams.
Off-center fed antennas may require tens of kOhms.

A resonant vertical (not necessarily full size) with large full-size radials
has a very mild requirements on choke common mode impedance.
But an elevated ground plane antenna with 3 or 4 radials needs a very good 
choke, or several of them.
And a vertical having a few very short counterpoises needs an extremely good 
choke.
Such an antenna is essentially an off-center fed dipole, placed vertically.

So, one either studies in detail the electromagnetics of his own antenna,
and determines the necessary common mode impedance of the choke by calculation,
or just puts in a very good choke (with measured common mode impedance)
on the operating frequency, and hopes for the best.

A choke with unknown common mode impedance
can be likened to a screw of unknown diameter and pitch.
It may fit your purpose, but it also may completely fail to do so.


73,

Sinisa  YT1NT, VE3EA
_
Topband Reflector Archives - http://www.contesting.com/_topband

Re: Topband: Hairpin Matching Coil Questions

[shristov]

A hairpin or a parallel matching inductor should be adjusted this way:
  1. select inductance (hairpin length);
  2. adjust wire length for the desired resonant frequency.

Repeat 1 and 2 until you get SWR = 1 at the desired resonant frequency.
Do not attempt to adjust resonance via hairpin length!

But in most cases inverted L needs no hairpin,
only the wire length should be adjusted for desired resonant frequency,
and a satisfactory SWR follows automatically.

Please note that the hairpin adjustment is NOT a substitute for wire length 
adjustment.


73,

Sinisa  YT1NT, VE3EA
_
Topband Reflector

Re: Topband: Lab style comparison results on 160m small lot antenna changes.

[shristov]

DAVID CUTHBERT telegraph...@gmail.com wrote:

 why must we continually test NEC against measurements? The work by N6LF has
 shown great correlation between simulation and the real world.
 
 Those of us who design electronic circuits (including EM) in the world of
 computer simulation have great faith in the various programs and NEC-4 (and
 possibly NEC-2) should give us an adequate A-B comparison.


The question of correlation with reality
must be answered for each particular sumulation.

NEC works most accurately with straight thin wire antennas.
It leaves much to be desired with telescopic tube elements,
and it fails completely to predict effects of booms in case of VHF/UHF 
antennas, etc.
In those and other cases, there are programs that work much better.

For example, WIPL-D computes telescopic tube elements
much more accurately than NEC (or MININEC),
and can also accurately model influence of booms
and other nearby conductors.


73,

Sinisa  YT1NT, VE3EA
___
Stew Perry Topband Distance Challenge coming on December 29th.

Re: Topband: Vertical Array Over Uneven Ground

[shristov]

Pošiljalac: Lennart M lennart.michaels...@telia.com

 That metric stuff is widely used around the globe.


It's fun to learn that Dr. Maxwell, the inventor of electromagnetic waves,
had used metric units exclusively 200 years ago.

So, why we cannot do the same today?


73,

Sinisa YT1NT, VE3EA

___
Topband reflector - topband@contesting.com

Re: Topband: More Amplifier info

[shristov]

Tom W8JI wrote:

 3.) Like any other device, they will fail with mismatch at high 
 power. They absolutely will require SWR shutdown and temperature monitoring.


I did a detailed study of this device last year,
and can confirm that the marketing story of being able
to handle SWR of 65:1 is an absolute nonsense.


73,

Sinisa  YT1NT, VE3EA

 
___
UR RST IS ... ... ..9 QSB QSB - hw? BK

Re: Topband: Ground loss query (re inverted L, antenna radiation resistance, Jerry Sevick)

[shristov]

wyc wycpub...@gmail.com wrote:

 I did some EZNEC modeling of a planned inverted-L, and came up 
 with some results that surprised me,
...
 I then repeated the exercise with a folded-inverted-L (i.e., with twinlead).
...
 What then surprised me was the feedpoint impedance when I switched to real
 ground, and the same few radials.  Instead of going to about 87 ohms (50
 ohms ideal antenna impedance plus 37 ohms of return path resistance), it
 went to about 200 ohms.


Folding has nothing to do with either radiation resistance or ground losses.
It is impedance-transforming device only.

You've just performed 1:4 impedance transformation, nothing else.

73,

Sinisa  YT1NT, VE3EA
___
UR RST IS ... ... ..9 QSB QSB - hw? BK

Re: Topband: 160 metre vertical with 'top loading'

[shristov]

Joe Subich, W4TV li...@subich.com wrote:

 Any coil that shows a 60% decrease in current through
 it has a significant amount of unexplained loss.


A current decrease (meaning less current at one end that at the other)
is not a loss, and it's far from being unexplained.

It's caused by the standing wave, just like the current decrease on a straight 
wire.
The general nature of the standing wave is not altered by the fact
that the wire is wound insted of being straight.

Consider helically wound vertical antenna.
The current decrease here is from 100 % at the bottom to 0 % at the top,
but it involves no loss (on it's own), just the standing wave.


73,

Sinisa  YT1NT, VE3EA
___
UR RST IS ... ... ..9 QSB QSB - hw? BK

Re: Topband: 160 metre vertical with 'top loading'

[shristov]

 W8JI is correct in that the current into a perfect inductor must equal the 
 current out of it.

Perfectly true.


 It's a piece of coiled wire so where else can the current go?

Wait a minute, a piece of coiled wire is not a perfect inductor!

It's a completely different beast:  the perfect inductor has zero length,
but a piece of coiled wire almost always has a substantial length
(the wire length, not the coil length), which causes all kinds of
transmission-line effects, including differing currents at coil ends.


 Tom's assumption here is a 'perfect' inductor with no distributed capacitance.

True, the 'perfect' inductor has no distributed capacitance, but, again,
perfect inductors are not what we have on our antennas.


73,

Sinisa  YT1NT, VE3EA
___
UR RST IS ... ... ..9 QSB QSB - hw? BK