On Sun, 19 Jul 1998, w8ji.tom wrote:
>
> You can not subtract either 6dB and/or 2.2 dB to get dBd freespace.
>
> 1.) There is no guarantee ground reflection gain is 6 dB, or any amount of
> "dB". It might even be loss!
>
> 2.) If you subtract 2.2 dBi from the yagi's gain, you get a number 2.2 dB
> less than the gain at the angle where gain was measured. You have no idea
> how that number relates to dBi unless you measured the antenna in
> freespace, or over perfect ground at the middle of the lobe maximum in a
> test range.
>
> 73 Tom
Tom is, of course, correct. The exact reference in the report is as
follows:
"At certain vertical angles and distances from the antenna, energy
reflected from the ground may constructively add to the energy coming
directly from the antenna. The maximum value of enhancement from this
effect is 6 dB."
So, it's a rather qualified 6dB and may, as Tom points out, be a loss.
Your mileage may vary.
73, Ward N0AX
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