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1-3 of 3 messages
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Page 1 of 1
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antenna height above ground
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by WB6BYU on September 24, 2004
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While testing some antennas this last weekend, we
measured the signal strengths at different heights above
ground when using horizontal polarization. The approximate
difference is 6dB increase when the height above ground
is doubled, at least over the range of heights typically
for a hand-held antenna. (This was for flat terrain
and line-of-sight to the transmitter: the difference can
be even greater when the signal is blocked by terrain
at low heights.)
So holding the antenna over your head can make a big
difference when trying to find a weak signal. And holding
the antenna close to the ground (presuming it is clear
enough, like a nicely mowed lawn) can provide over 20dB
of attenuation if the signal gets too strong to take
a bearing. The antenna pattern is maintained even at
a few inches above the ground.
Has anyone else experienced this difference?
The next step will be to run similar tests using vertical
polarization, though it is harder to get the feedpoint
very close to the ground due to the antenna height.
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RE: antenna height above ground
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by WA6BFH on January 28, 2005
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The basic practice that you suggest is a common methodology for use in antenna test ranges. The antennas are kept low to the ground (less than a quarter wavelength), and in the case of beam antennas are rotated to check the pattern.
As an additional concept that may help your thinking and assessment, what is the dB change as defined by the "Inverse Square Law"?
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