[Lf] [Fwd: LF: Counterpoise Experiment]

[Andre Kesteloot]

Les Rayburn wrote:

> At 15:11 6/5/02 +0200, you wrote:
> >Hello Jim,
> >
> >keep in mind that an elevated counterpoise will reduce the effective
> >height of the antenna (by "pulling up'' the RF ground level.
> >So a part of the improvement could be lost again due to the lower
> >radiation resistance of the antenna.
> >It is interesting to notice that the counterpoise increased the total
> >antenna current by 7.5% (32 Ohm vs 37 Ohm) while it takes 20% of the
> >current. Maybe it is a bit simplified, but based on that 20% one could
> >assume that the RF ground level was raised by 40cm (20% of 2m).
> >In that case the effective height would decrease from 9.5m to 9.1m (-0.37dB).
> >The increased current (7.5%) gave an improvement of 0.63dB, so the overall
> >gain could be as low as 0.26dB.
> >
> >It seems that an isolated counterpoise is only worth the effort with :
> >- high antennas (so the loss in effective height is minimal)
> >- a lot of space (and $$ to buy the wire)
> >- very tolerant XYL and neighbours
> >
> >73, Rik  ON7YD
>
> I'll have to respectfully disagree with Rik on this one.
>
> There are lots of advantages to the use of counterpoises on LF. The biggest
> one being
> that the antenna is a lot more resistant to de-tuning from weather, dew,
> etc. Using
> high-Q coils, losses from even small amounts of de-tuning can be very high
> indeed.
>
> Also, I'm currently using a "stealth" counterpoise. Insulated #14 AWG house
> wiring has
> been stapled to the underside of my outdoor deck (which is very large).
> I've literally
> covered the bottom of the deck with wire. It is completely hidden from
> view, was
> much easier than attempting to bury wire, and the cost was minimal. Less
> than $50
> dollars total by buying the wire on sale at home improvement stores.
>
> My tuning coil is mounted to a wooden post on the end of the deck, and a
> flattop three-wire vertical is positioned on two masts on opposite ends of
> my yard. All this on an average 1/4 acre lot.
>
> Performance is unchanged vs. my former extensive ground radial system which
> could only be used during the winter months.
>
> I'm a huge fan of counter-poises and think that more amateurs should
> give them a try. Since most of your losses occur at the base of the antenna
> and it's virtually impossible to lay down resonant radials at this frequency
> anyway, even small counterpoises can perform better than most
> ground radial systems within amateur limits.
>
> 73,
>
> Les Rayburn, N1LF
>
> Les Rayburn, N1LF
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