Steve - This is a good question and one I have been struggling with as
well. I am a new, 3 time rover, so we are in much the same boat.
After some consideration, study, a little analysis, and conversations
with other rovers, I have come to the conclusion that, as a general
rule of thumb, the minimum height for a rover antenna should be a half
wavelength over any conducting surfaces a half wave or larger within a
couple of wavelengths of the antenna.
A half wave is the lowest height above ground that has no overhead
radiation and starts to concentrate the radiation at low angles. Low
angle radiation is the key to working troposcatter and most of your
rover contacts will be by troposcatter at least when sporadic E is not
in.
The key to troposcatter concentrate as much radiation at low angle as
possible. This maximizes the volume of atmosphere available to use as
a scattering volume. Some studies indicate that for every degree the
angle of radiaiton is lowered, there is a gain in signal to noise
ratio (not antenna gain) at the other end of about 10 dB. So the
significant parameter of interest to look at is the angle of
radiation, and gain at that angle, rather than just straight gain.
While this is fairly easy to achieve on two meters, where a half wave
is about 40 inches, it is harder on 6 meters where a half wave is 10
feet on 6 meters, at least if you want to do it in motion. If I recall
correctly, you have a pickup truck. As a minimum, I suggest that you
try to have the 6 meter antenna at least 10 feet above the bed and the
2 meter antenna at least 40 inches above the cab roof.
If you can't achieve this in all directions, park so that the
direction where the antennas clear the ground is toward the direction
where you want to have the loudest signal. I have a station wagon and
the 6 meter antenna is at 14 feet, so I am acutely aware of this.
Drop offs help, but you need to be fairly close to them.
You don't need to use the same strategy in every contest. My gut
feeling is that the telescoping mast is the way to go, at least in
September and January where activity is low and the probability of
sporadic-E low. In June, where there is more activity and 6 meters is
hopping (not in 2007 though) you may well be able to forego the
telescoping mast and come out ahead because of the increased activity.
How is the CW going? That is the easiest way to add 10 dB to your
signal. - Duffey
--
KK6MC
James Duffey
Cedar Crest NM
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