Copper Talk » Open Forum » Archived Messages » 2002 » 09/01/2002 to 09/30/2002 » Rooftop mobile antenna « Previous Next »

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GrooveTube
Posted on Monday, September 16, 2002 - 1:38 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

Anybody ever used, lets say, a K40 on the roof? I have an old mag-mount (K40) I'd like to stick-up there. Any issues? I am wondering if the vehicle becomes part of the ground-plane on the car, so would this work on the roof? No metal up there, just the standard ashphalt shingle. Thanks-
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bruce
Posted on Monday, September 16, 2002 - 9:15 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

groovetube youll have a problem making it work now you could take 3 102 inch wires and connect them to the coax sheils under the base and fan them out that would work been there and done that on a old k40
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Tech671
Posted on Tuesday, September 17, 2002 - 5:59 am:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

It will show a poor swr without a GP. Bruce has a good idea, using (3) 102s fanned out just magnetized to the magnet may work. Of course by the time you buy the 102s you coul've bought an Imax 99 (or just about).
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DeadlyEyes
Posted on Tuesday, September 17, 2002 - 9:54 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

Re Tech 671...

I think the 102s that bruce is thinking of is not a 102 steel whip. If I read his post correctly I think he intends to mean 3 wires (speaker wire, telephone wire, any kind of wire) each 102 inches long. You could probably use just some plane old discared telephone or rotor cable wire.

And a technical point. I remember reading in my antenna books that the ground plane elements should be 5% longer than a quarter wave.

But then again, sometimes in actual practice you need to massage what is in the books.

However I do agree with you in that a proper base antenna would produce much better results.