John Geiger wrote:
> Another local VHFer and myself were having a
> discussion as I was driving to work today about
> antenna height for VHF. One thing we wondered about
> is if there is an "optium" antenna height for VHF, or
> is "higher always better." Is there a point where the
> extra height isn't worth the cost of tower, coax, etc,
> and the extra loss in the coax-in terms of the
> increased distance you will work? Or does extra
> height always outweight these other factors?
>
> 73s John W5TD
>
>
>
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John,
It's been my experience that there are two answers to the question: 50
MHz, and the other higher bands.
On 50 MHz, I think the key is to match the radiation angle of the
antenna to the incoming signal. There are two reasons for this: 1)
Because the radiation angle of 50 MHz antennas at realistic heights are
usually significantly affected by height above ground, and 2) Signals
from the various 50 MHz propagation modes often have wildly varying
arrival angles. 50 MHz F2 signals usually arrive at low to moderate
angles, E-skip signals usually arrive at moderate to high angles, and
ground wave signals usually arrive at low angles. So you can see, there
are a varying heights which could be "best".
At 144 MHz and up, you local geography and any obstructions plays a
major part. Most signals on these bands are low angle, and because a
wavelength is short at these frequencies, the radiation angle from
realistic antennas about 144 MHz are not significantly affected by
height above ground. For these reasons, 30 or 40 feet is high enough if
you have a hilltop QTH or a flatland QTH with no local obstructions.
Most of us don't have these "perfect" QTHs, and find that greater height
is beneficial.
For realistic QTHs, 70-80 feet is probably "good enough" in the absence
of major obstructions or tall trees. The latter can be a real absorber
of signals on in the higher VHF and lower UHF spectrum.
73,
Dave/K8CC
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