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Old November 26th 04, 08:44 PM
Dave Platt
 
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Has anyone tried mounting a magnet mount hf antenna (Hamstick) on the top of
a metal toolbox, the kind that are used in the back of pickup
trucks......just curious...I realize the best place is on top of the
cab....tnx...Gary, K8BY


There are two aspects to this: mechanical and electrical.

Mechanically, I'd imagine you'll be OK. A Hamstick is pretty thin,
and wouldn't have a large amount of wind-drag force on it. Assuming
that the toolbox is solidly constructed, the magmount's grip on its
roof would be sufficient to keep the antenna in place, and the drag
and torque on the toolbox lid's hinges probably wouldn't be enough to
matter. If I were you I'd arrange to snub the feed cable - clamp it
down to the frame somehow, so that if the mag-mount does pop loose you
don't find yourself dragging the antenna on the road behind the vehicle.

Electrically, there are a couple of issues. For one thing, if the
tookbox is immediately behind the cab, this arrangement might put the
Hamstick quite close to metal portions of the cab roof or uprights.
This sort of close antenna-to-body coupling tends to reduce the
antenna efficiency. Keep the antenna as far away from the metal body
as you can safely manage.

From what I've read, HF magmounts often don't have enough coupling
capacitance to give a really satisfactory grounding, even when mounted
right on the roof. It's usually desirable (and often necessary) to
run a short, fat grounding lead from the antenna base/feedpoint to a
solid grounding location on the vehicle frame. You should probably do
something like this if you do decide to mag-mount on the toolbox.

--
Dave Platt AE6EO
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