Hi Jerry,
65% is in the wheelhouse for DOG VF's. 400 to 600 ohms seems high. In the
12 county area around Raleigh/Durham/Chapel Hill, we measured 120 - 200
ohms resonant R.
The variation you experienced, and also high R readings could be explained
by a few nicks in the wire insulation toward the ends, which could have
been there to start with, or perhaps you experienced critter nibble, or
perhaps the ends were inadequately insulated from ground contact or the
elements.
DOG conductor in contact with ground moisture near the ends could
completely skewer results. That's an electrical 1/4 wave between center and
either end of the DOG. Inadvertently grounding an end will be transformed
around the surge impedance of the wire to a quite higher impedance at
center. An inadvertent partial grounding near the ends along with variation
in ground surface moisture would explain erratic observations of high R and
no resonance.
73 & Good Luck,
Guy K2AV
On Fri, Jul 26, 2019 at 10:34 PM K4SAV <RadioXX@charter.net> wrote:
> K2AV said:
> "Measured resonance of a fixed length gave us velocity factor (VF) and
> other data. VF's based on those measurements ranged from 45% to 85%.
> That huge variability certainly explained the BOG experience, and
> suggested a solution, but that's another subject."
>
>
> When I did those tests at my house the velocity factor of a dipole on
> the ground was usually about 65% but many times there was no resonance
> at all, so no way to calculate velocity factor. Total impedance was
> usually 400 to 600 ohms but resistance and reactance were all over the
> place. That dipole was tested on the ground at various times over a one
> month period and never moved. I can only guess that must have been due
> to variations in ground moisture content.
>
> I was also trying to use that data to help explain BOG performance, but
> I didn't have much success.
>
> Jerry, K4SAV
>
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