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Author Topic: Counterpoise question  (Read 642 times)
WD6EJN
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Posts: 1




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« on: February 22, 2003, 06:21:23 PM »

My antenna is a kite antenna with about 400 ft of
no 22 wire to an sgc tuner I fly from the car!
When I find a place to fly it (not many) I throw out
three or four ground wires made from heavy duty extension cords I bought at a discount store, I just plug them into a cube tap which is simply shorted at
the plug end, I can make them any length by just pluging them together parralel for the higher bands or serially for 80-160.
I usually use 1/4 wave lengths for an rf ground then
have a dc ground as well for my ham shack.
Can I just lay out the cords in a random manner for the kite antenna ground, or would it be better to have each leg exactly 1/4 wave?
Can I just use random (longer)50-80' lengths for each leg as a dc ground or is it important to have 1/4 wave to maintain 50 ohms?
It would be nearly impossible to change the length of
the ground wires every time I change bands.
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KF4ZGZ
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Posts: 277


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« Reply #1 on: February 24, 2003, 07:07:59 AM »

I would use a counterpoise for the lowest band and accept what you've got with everything else. No fact, just an opinion.
Matt, kf4zgz
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WB2WIK
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Posts: 20540




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« Reply #2 on: February 24, 2003, 12:01:47 PM »

There's no good answer to this, because:

1.  You don't ever need a "DC ground."  This has nothing to do with antenna performance, and mobile stations never have a DC ground -- it doesn't matter.

2.  Whether you need radials or not, and how long they should be, depends on the exact length of your radiating antenna.  "About 400 feet" doesn't tell us that.  Every time your antenna is an increment of one-half wavelength long, it becomes voltage fed, and requires no counterpoise system.  Every time your antenna is an odd increment of one-quarter wavelength, it becomes current fed, and relies heavily on a counterpoise or image plane in order to function.

So, if you're not changing the radiator length every time you change bands, and you don't really know how long it is electrically, it's impossible to predict what radials will, or won't, do.

In general, though, even if your antenna is voltage-fed and requires no radials, the presence of radials won't hurt anything; with that in mind, I'd lay out as many as possible, as long as possible, and live with that!  The extension cords and cube tap are a pretty neat idea.

WB2WIK/6
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WD6EJN
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Posts: 1




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« Reply #3 on: February 26, 2003, 04:31:05 PM »

I thought it didn't matter with a long wire when
the antenna could be many wavelengths long.
If the actual length of a long wire and ground combination is important,,then I can actually very
easily change the length of both, although I think
I am getting so much signal out that it probably doesn't matter.
If I let the kite out all the way it is exactly 400'
But I can let out any length I want! in fact I have
even grounded the fishing reel and letting
out the antenna till the impedance of the spool is shunt fed close to 50 ohms (almost all the way out). It is a lot easier to let out what ever the local situation dictates,, flying kite over homes, near an airport or gusty wind, I don't know if it makes any difference if the auto tuner sees an impedance close to 50 ohms or not, it's a lot easier to just let out a random length of wire, since the spool is isolated from the antenna anyway.
Stark contrast when I have to run less than 10 watts
in a cc&r invironment!
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