On Sun, 26 Sep 2004 09:33:47 -0400, "Noltz"
wrote in
:
snip
So I guess my only question left is tuning. Can I tune a ground-plane
type antenna if there is no ground plane at the back of the truck? If it's
mounted to the edge of the bed, the ground plane would be a 4" by 6 foot
strip of metal, not counting the floor of the box, of course. I've seen
antenna's mounted there before, but I have no idea if they work.
They work fine. And the reason they work fine is because of the
confusion between 'ground-plane' and 'RF ground', as I stated before.
The location you have chosen for your antenna should provide a good RF
ground, and that's all you need.
The antennas that are frequently referred to as "ground-plane"
antennas are usually base antennas that have an -artificial- ground
plane. A mobile antenna uses both the vehicle and the ground below the
vehicle as the ground plane, so there is no need for an artificial
ground plane.
IOW, your mobile antenna already has a ground plane regardless of
where it's mounted.
Here's my
options;
1) a 2' or 3' whip mounted to the left front fender, using the hood as a
ground plane.
2) a 2' whip mounted to the center of the roof, using that as a ground plane
3) a 4' whip mounted to the edge of the bed at the rear of the truck, with
no effective "ground plane" available.
Which of these will give me the best performance for my money?
.....uh, the 102" whip on the bumper. I have mine mounted dead center
on the donkey-guard in the front and tied back. Even when tied back it
works better than a 4' fiberglass whip. But if I can't talk you into
the bridge-buster, just remember that longer is better, and anything
shorter than 3' is mostly worthless beyond a few hundred yards.
I will be
buying a SWR meter since 2 or 3 others at the shop will also be installing
radios.
Forget the SWR meter and buy a "field strength meter". Reason: A dummy
load has an SWR of 1:1 but is a very poor antenna; a field strenth
meter measures the field strength directly, which is the point of
tuning the antenna in the first place. And they both cost about the
same (actually, the FSM is even cheaper if you have another radio with
a good signal meter!).
I'm looking at FireStik brand kits, as they've been recommended
everywhere and have an easy-to-adjust tip.
Other antennas are just easy to adjust using a hex wrench -- loosen
the set-screw, slide the whip up or down, then tighten the set-screw.
Either way, both types score pretty low on the even-an-idiot-can-do-it
scale. Just don't limit yourself (and your wallet) to brand-name
products because they claim it's "easy to tune".
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