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@artekmanuals.com <mailto:Manuals@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@ArtekManuals.com
www.ArtekManuals.com <http://www.ArtekManuals.com>
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