[Elecraft] Re: Best way to secure RF ground from 2nd floor- a related question

[Don Wilhelm]

Bob,

The best way to tune the counterpoises is to use an RF current probe and 
tune for maximum current in the counterpoise wire.  Several designs for 
RF current probes have been published in QST and other journals in the past.

An old method (which still works) is to put an RF ammeter in series with 
the counterpoise wire to tune it.

You are correct, cutting a wire to some formula will not necessarily 
yield optimum performance - the counterpoise wires are usually mounted 
low and close to earth and other objects - that proximity will detune 
them, sometimes drastically.

To use the MFJ259, I would think the easiest would be to split the wire 
in half and measure its resonant frequency (with both ends connected to 
nothing) - it would be a half wave dipole on double the frequency - 
prune for zero reactance and reconnect the cut made in the middle of the 
wire.

73,
Don W3FPR


Solosko, Robert B (Bob) wrote:
>  Hi All,
>
> 	I have a related question: how do I tune the counterpoises?
>
> 	My shack is also on the 2nd floor and I had major problems with
> RF in the shack on 15m, 17m and 20m. My antenna is a 100' dipole
> connected with ladder line to a 4:1 current balun that's just outside
> the window where my shack is. Then I have 5' of RG-8 running through the
> window to my KAT100 inside. I also have the braid from some old RG-8 as
> a ground wire running from the KAT100 through the window to an 8' ground
> rod. I had RF in the shack problems with this arrangement that was
> mostly resolved by connecting 3 counterpoises to the ground side of the
> balun, one for each band. It's not perfect, but it's a major
> improvement. The counterpoises were cut approximately for each band - so
> the question is how do you tune the counterpoises, since the effects of
> RF in the shack at this point are somewhat subtle. 
>
> 	I just purchased an MFJ 259B antenna analyzer (mine actually
> seems to work out of the box!), but I don't see any obvious way to use
> it to tune the counterpoises, since the counterpoises are just heavy
> insulated wire, and not coax. Can the antenna analyzer be used to tune
> the counterpoises? If not is there some other way to do so without
> needing other specialized equipment?
>
> 	Thanks.
>
> Bob W1SRB
>
>