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Old April 11th 06, 09:23 AM posted to rec.radio.amateur.antenna
Harbin
 
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Default Counterpoise wire length

Looks like I'm looking for a 1/4 wave. Thanks

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SeeYaa Harbin Osteen KG6URO

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Harbin wrote:
Counterpoise wire length. I've heard that it should be 1/4 wave, and then again I've
heard it should be 1/2. Which is correct, or will they both work?


The lowest impedance presented by a single counterpoise wire is when
the counterpoise is resonant and 1/4 wl long electrically.

When a single counterpoise wire is near 1/2 wl long and resonant, it
has a very high end impedance.

If the counterpoise is under a dipole or some other antenna just to
isolate it from ground losses, a 1/2 wl long counterpoise or longer is
best.

If the counterpoise is used as a termination to allow forceing current
into a Marconi antenna or an end-fed antenna, or used to provide a
ground path for unwanted currents, it is best if it is 1/4 wl long.

More counterpoise wires are always better, because the more you use the
less critical length is and the lower loss is. There is of course a
point where more won't help. With 1/4 wl wires, 50 or so placed
radially are near perfect. Adding more won't make a noticeable
difference. Once the counterpoise wires are .025 to .05 wavelengths
apart at the widest points, adding more will generally not help.

I use 100 200 foot long wires on one of my 160 meter verticals. On my
other verticals I have 1/4 wl radials, and once I reached 40-50 radials
adding more made no measureable difference at all.

73 Tom