I don't have the June issue of QST yet. I couldn't wait, so I went to
the ARRL website to read it, hoping for some enlightenment.
It is unfortunate that most of his measurements were done on a buried
BOG. Most of us don't have buried BOGS for comparison. Most of us
don't have NEC4 either.
He did measure the resonant frequency of a dipole 1 inch above ground
and found that it agreed with NEC analysis. He plotted the parallel
resonant point, The series resonant point for that 300 ft dipole should
be close to 1.05 MHz. My NEC analysis agrees with his. NEC says that
my 118.25 ft dipole should have a low freq resonant point at 3.05 MHz at
2 inches above ground or 2.8 MHz at 1 inch above ground. It measured
2.25 MHz. So that is a major disagreement. I had to set the wire at
0.2 inches above ground in NEC to duplicate the measured resonant
frequency and it is actually 1.5 to 2 inches above ground. That gives
me at least one data point from that article to investigate, although at
this point I don't know were to start. Suggestions welcome.
Too bad he didn't compare a normal BOG with measured data for that BOG.
It is interesting to note that he has been using a 450 ft BOG on 160 for
3 years. It would be normal to expect the performance to decline
severely if this BOG became partially buried. Heck even a heavy rain
will lower the gain by 6 dB on the BOGS I have tested. Actually NEC
produces a good pattern and RDF for a 450 ft BOG. The real question is
what is the actual pattern?
Jerry, K4SAV
On 5/13/2016 3:40 PM, Carl Luetzelschwab wrote:
With the recent thread of modeling BOGs, I hope those interested in this
endeavor read Rudy N6LF's article in the June 2016 QST. In the article he
compared modeling to measurements on three antennas: one was low to ground,
one was buried and the third was a vertical with just one ground rod. This
then led to modeling his degraded BOG to understand why it degraded. This
short paragraph does not do his work justice - go read his article (and the
longer version cited below).
For all this modeling he used the NEC-4.2 engine, and the results were very
good when NEC wire rules were obeyed, the dimensions were accurate and the
ground characteristics were measured and used in the model (not the canned
poor, average and good grounds).
The longer article with all the details is available on the ARRL web site.
Carl K9LA
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