Topband: Beverage performance VS term resistor

[Artek Manuals]

Thanks...I did not know that. I am running Eznec+ 6.0 here which is 
based on a version of NEC2 but the GUI doesn't address RDF ( will have 
to give Lewellyn a poke about that 8^)

Dave
NR1DX

On 1/24/2020 9:25 AM, Don Kirk wrote:
> Hi Dave,
>
> I use 4nec2 which is free, and it provides direct readout of the RDF 
> value.
>
> Don (wd8dsb)
>
> On Fri, Jan 24, 2020 at 9:21 AM Artek Manuals 
> <Manuals at artekmanuals.com <mailto:Manuals at artekmanuals.com>> wrote:
>
> Steve
>
> I am curious, what antenna modeling program are you using that gives
> direct readout in RDF? Or are you� "estimating"� it from the antenna
> graphical pattern?
>
> Dave
> NR1DX
> >> The recent experiments with my Beverages in the cold weather
> has raised some comments about the termination resistor and the
> antenna performance.� I received a few emails asking about F/B. I
> made the comment that it really is'nt worth the effort trying to
> get the termination value exact. Close is good enough.
> >>
> >> Changing the termination resistor value has only a limited
> effect on the RDF of the antenna.� The F/B can change some what,
> but the zenith and side rejection is mostly preserved independent
> of the termination value.
> >> This is well described by John in the the Lowband DXing book.
> (5th edition, pg 7-64 �conclusions�)
> >>
> >> Today I did some modelling on a 920� wire.� RDF with a 500 Ohm
> term is 11.7 dB, with 200 Ohm term it is 11.3 dB, and with 800 Ohm
> term it is 11.4 dB.� So only about .4 dB of RDF change with a very
> significant (+/- 300 Ohm) resistor change.� Looking at the azimuth
> and Zenith plots, the front-to-side remains mostly unchanged while
> rear lobes develop that diminish the F/B.� However, unless there
> is a specific noise, or QRM problem from the back of the
> Beverages, this will likely go un-noticed.� The important
> parameter is RDF�.the rejection of noise in the full 3D hemisphere
> compared to the max forward gain.
> >>
> >> In fact, I modelled no termination (by inserting 1 e6 Ohms as a
> term resistor) and the RDF of the bi-directional Beverage is still
> 9.7 dB. (almost zero F/B) This is pretty decent, and is better
> than many other small loop antennas and smaller arrays.� The
> azimuth pattern still shows significant side and zenith rejection
> which is why the RDF calculates so well.� This is perhaps why many
> ops have had good success with bi-directional Beverages.
> >>
> >> If you are unfamiliar with what the RDF metric, Greg has a good
> explanation here:
> http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/RDFMetric.htm
> <http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/RDFMetric.htm>
> >>
> >> 73, de steve ve6wz
> >> _______________________________________________
> >>
>
> -- Dave
> Manuals at ArtekManuals.com
> www.ArtekManuals.com <http://www.ArtekManuals.com>
>
> _________________
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> Reflector
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-- 
Dave
Manuals at ArtekManuals.com
www.ArtekManuals.com