On 13 Sep 2005 16:15:08 GMT, "Bill Turner" wrote:

Richard Harrison wrote:

Phil found a simple dipole only a few feet above ground would
outperform a mobile whip on 40 or 75 meters.
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Without more information, this comparison is flawed. A mobile whip has
a lower angle of radiation than a horizontal dipole. On 40 or 75, the
vertical component of radiation can be quite significant for close-in
stations (100 miles or so). At night, working long distances, the whip
may outperform the dipole. During the day, the dipole will probably
outperform the whip.

It all depends.
73, Bill W6WRT


Correct on radiation angle, however the average mobile whip at 3.8mhz
is around 10% efficient. Even at 7Mhz it doesn't improve much
efficientcy wise. The low dipole (low being less than .25WL) is
close or better than 95% efficient but has a rotten radiation angle
for DX however close in it will be very good.

Myself in that situation.. I'd put a poles at either end of the
trailer (thats 50ft length) and if possible get it up 30ft or better
and hang a dipole. If the antenna is 66' (40m) the excess length
can hang. The support poles can be anything that will stay up. At
20m 30ft is 1/2WL up and will be decent. Even if you can't do two
support poles and only one make that one high as possible and mount
a dipole as a sloper. It will be somewhat directional but performace
will be far better than any ground mounted vertical that has no ground
plane.

If money wasn't a limiting factor. put down a base and put up a
freestanding tower.

The rules remain. More metal, higher the better.


Allison
KB1GMX