In EZNEC the RDF number is the difference between the average gain and
the gain at the elevation angle you select. W8JI uses 20 degrees as the
reference and some other systems use a slightly different angle. You
have to run a 3 dimensional plot and the average gain number will appear
at the bottom of the main page.
Jerry, K4SAV
On 1/24/2020 8:43 AM, Artek Manuals wrote:
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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