The 102" whip is not tunable except by adding or taking away the spring from
the ball mount. As I said the 102 never was a perfect match anyway with
about 36 ohms of radiation resistance instead of the desired 50 ohms for a
near perfect match. Since the 102 is not a perfect match the coax length
does matter but if it did match close to perfectly then coax length would
not matter. As for the "counterpoise", that is just another name for the
ground plane. Yes the counterpoise/ground plane is important but any metal
car or truck body has enough metal to form a good ground plane. The vehicle
body is half of the antenna and the 102" plus 6" ball and spring is the
other half of your center fed, half-wave dipole antenna system. As far as
SWR depending on the "counterpoise", the antenna must be mounted, as I said,
with plenty of metal all around it or to put it another way in the middle of
your vehicle roof to give it a good ground plane/counterpoise. If people
enjoy getting their 102 to "flatline" by using 18 feet of coax and having
good performance that's fine but their antenna is not going to work any
better than if they had the proper half-wave length of coax and the small
amount of reflected RF should not hurt their system.

Scorpio
"Nannar Sin" wrote in message
news
On Mon, 15 May 2006 14:47:42 GMT, "GHB"
wrote:

Make sure your mobile has low SWR before installing an amp. You should
be
using an exact half-wave length of coax in your mobile which, depending
on
what coax, will be around 12 to 13 feet but not 18 feet as so many people
say.

Oh boy is this an old argument.. I dont even want to get started.
Search google this has been talked about forever in here. Some of the
most successful key down guys have used 18 feet and are successful
talking skip and shootouts. Truth is the swr of your antenna will
depend on your counterpoise. Oh well if your antenna is tuned properly
the amount of coax may not matter.

A real old timer!