First of all, many many thanks to those of you who responded to my original
posting. Your
thoughts were both insightful, and extremely interesting.
As to the antennas, the clear winner was the Georgia Bugcatcher ( just kidding
you Texas )
and the Carolina Bugcatcher seems very similar. Their disadvantages are that
you must get
out of the vehicle to change bands, and they have a fairly high wind loading.
The screwdriver antennas by High Sierra and BB3 also rate alongside the Bug
collectors.
Others mentioned were the Hustler, Outbacker, and a few obscure ones. These
definitely
came in last.
Thanks also to the gentleman who sent me a program called "mobile.exe". It's
ARRL shareware
and allows one to change any of the many variables of a shortened antenna. (
matter of fact,
it probably could also be used for antennas larger than a mobile with good
results )
The bottom line is that a center ( or up to 66% ) loaded antenna is absolutely
a necessity,
and the DIAMETER of the COIL MUST BE LARGE!!! If not, coil losses will eat you
alive.
For example, the Hustler coils have a loss of between 42 and 47 ohms. Add that
to a ground
loss of between 2 and 12 ohms, and you'll see why the things match so well.
Here again, I'm
afraid (myself included ) that we let the SWR god take us for a ride. Base
loaded antennas are
next in line to the center loaded one.
Rather a surprise to me to discover that ground loss is a function of the
height above ground
at which the antenna is mounted. Typical values range from 10-12 ohms for a
BUMPER mount to
4-6 ohms for a midmount ( about 4 feet off the ground ) to around 2 ohms if you
mount the
thing on the roof of the vehicle.
SO, a center loaded mast with a LARGE diameter ( 3"is best )coil will put you
in the range
of 40-48% efficiency. And of course, the longer ( taller? ) the beast is, the
better.
Again, my thanks to all of you who responded. I've been playing with antennas
for over 40
years, but my entry into the mobile field is brand new, and there are a lot of
very
knowledgeable gents out there.
And it's nice to be on a reflector with all of you.
Thanks a $$$$$$$.$$-the $350 or so I'm spending for a new antenna.
73,
ED
-------------------------------------
Name: Ed Sleight
E-mail: k4sb@avana.net
To: <towertalk@contesting.com>
Date: 1/8/97
Time: 2:36:07 PM
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