"Hal Rosser" wrote in message
...

"Jimmie D" wrote in message
...

"Rob" wrote in message
...
On Mon, 23 Oct 2006 01:12:09 GMT, "Merlin-7 KI4ILB"
wrote:

I just bought a 10 meter mobile rig (25 watt old radio shack rig).

I was planing on cutting down a 102" CB whip to 10 meter band.

Anyone know of any type of antenna that would work better?

Thanks
Joe
KI4ILB


I know this is an old post, but I only just now found and read it,
so I hope it is of interest to someone, if not the original poster.

Now that that's over, (whew) I installed a 102" SS whip, spring, and
ball mount I got from Rat Shack on the side of my 94 Plymouth Sundance's
left rear fender, (the trunk lid is fiberglass so I couldn't mount it
there)
and it works great as it was. I got a near perfect match across the 10
meter
band without a tuner and I didn't have to trim it one iota. If I
needed,
there is a little room for adjustment in the mount as the whip is
secured
with a hex head set screw in the mount. That should give enough wiggle
room
to get a decent match without having to cut the whip.

I have a tuner, (a Drake MN-4) I use in the car, but I use in bypass
mode for 10 meters. It will tune the whip from 20 through 10 meters with
an
SWR typically under 1.5:1 on all those bands. It won't tune to a useable
SWR
for anything lower in frequency than 20 meters though, so I will have to
come up with another antenna that I can hopefully use with the same
mount
for 40, and hopefully through 80 meters.

Again, I know this is a reply to a nearly 7 month old post, but I
hope it is of use to someone anyway.

Rob


The long antenna probably tunes up on 10M because of the fiberglass trunk
lid. Had the lid been metal it would have been the responsibel for the
largest portion of the capacitance needed to resonate the antenna.
Without this capcitance the antenna will need to be longer than normal to
achive resonance on 10M. One advantage of this that you have noted is a
better match to 50 ohms. Longer antenna = greater L, fibergllass lid =
less capacitance which gives a higher LC ratio at resonance.

Jimmie

He mounted the antenna on the fender (because the trunk was fiberglass).
With that in mind, how does the trunk lid being fiberglass lessen the
capacitance of the circuit?
Doesn't the fender 'take the place' of the trunk lid?
I would reccommend someone using a metal trunk lid as a mounting surface
to install some copper wire jumpers from the lid to the rest of the body.
Some folks even go ahead and install copper jumpers to join all parts of
the body to each other and to the frame, motor, and neg battery terminal.



Which do you think will offer more capacitance to the antenna, a metal trunk
lid wich is a 90 degrees to the antenna and relaatively wide or the narrow
fender that falls away from the antenna quickly.

Jimmie