6 dB whenever you double antenna height at VHF? That sounds a bit optimistic, actually that sounds very optimistic...
Lets see if modeling backs up the claim...
For this test we have a 2 meter 1/4 wavelength antenna measured at 1, 2, and 4 wavelengths high over average ground to test the 6 dB gain every time you double height claim...
So doubling height from 1 to 2 wavelengths high nets 1.7 dB in gain, and going from 2 to 4 wavelengths high gets you an additional 1.27 dB in gain. I have doubled the antenna height twice and only see 1.97 dB total gain. There goes the 6 dB gain every time you double the height idea...
Just to make sure being to close to the ground is not the issue here lets continue this some more...
Here we see 8, 16, and 32 wavelengths high. For a point of reference for those of us who use the imperial measurement system, 32 wavelengths at this frequency is over 200 feet high. That is beyond the height most people will ever get with such an antenna...
The peak gain of 6.49 dBi is only 4.01 dB in gain over an antenna mounted significantly lower than that antenna. Further, the next doubling of height results in a pretty significant drop in gain and a noticeably higher take off angle... Apparently, in this case, to much height is a possibility...
Further, it was stated here that there would be a difference in the transmit and receive gains. The Reciprocity Theorem disagrees with that assessment completely.
You claim that is a Motorola guideline? I've never heard of it, any reference to back that up?
The gain you get from increasing height at VHF is more to do with clearing obstacles and, as has already been stated...
The DB
