[VHFcontesting] Brain pickin' time

[James Duffey]

Mike - You asked:

"...for a rover what are your "opinions"... for the minimum, and  
maximum height for a 4 band (50/144/222/432) portable tower..."

The minimum height for a rover antenna should be such that it is a  
half wave away from the nearest metallic surface. Less than a half  
wave and most of the radiation is straight up where you don;t want it,  
particualrly for troposcatter.Usually this is the roof of a car. A  
half wave is about 10 feet on 6M, and I find that my loop is just over  
10 feet away from the roof of the car when it is about 12 feet above  
ground. That requiement may be difficult to achieve in some  
installations. At stops, I can extend it to over 15 feet and it does  
perform a bit better.

On two meters a half wave is 40 inches and this criteria can be met  
pretty easily, although it may be a stretch for roof mounted antennas.

On the higher bands, there should be no problems getting the antenna  
this high.

A second consideration is to get the antenna above local obstructions.  
In most cases, 10 to 12 feet will do OK for this.

As to maximum height, that is probably driven by your pocket book, not  
only in tower cost, but also in feedline costa and gasoline costs. A  
bigger consideration may be how long it takes to erect the antenna,  
and the complications of that. Stopping and operating without any  
preparation is clearly the best. Stopping, getting out, pushing up an  
antenna on a push up mast, or folding over an antenna and extending  
it, takes only a few minutes. Stopping, getting out, setting  
outriggers, installing antennas, and cranking up a tower all takes up  
a lot of time and that is time that could be better used making  
contacts.

Still a rover with a long boom Yagi at 30-40 ft on 6M certainly has  
its attractions. - Duffey
--
KK6MC
James Duffey
Cedar Crest NM