[Elecraft] O.T. Tuning a Counterpoise

[Drew AF2Z]

Tks, Ron- I'll keep that in mind. My counterpoises lie on a flat roof 
adjacent the shack. I've never tried to tune them other than initially 
cutting them to theoretical best length; I suppose they could be better...

73,
Drew
AF2Z



On 07/16/16 13:39, Ron D'Eau Claire wrote:
> One approach to reduce "RF in the shack" using an end-fed wire is to
> resonate the "counterpoise" for the band you are using. MFJ made just such a
> "tuner" (model 931 IIRC) but any tunable L-network will work. The idea is to
> adjust the "tuner" for maximum current flowing into the counterpoise
> (meaning the counterpoise is offering the lowest possible impedance to the
> equipment it is connected to.) I have successfully used that in a 2nd story
> apartment feeding an end-fed wire running outside. I know one Ham who bought
> the MFJ box and found it worked FB.
>
> For a homebrew "counterpoise tuner" you'll need an RF ammeter but a good
> cheap one is an incandescent flashlight bulb in series  where the
> counterpoise connects to the rig chassis. Tune for the counterpoise for
> maximum brightness with the rig running at the lowest power that will light
> the bulb, then short-circuit the bulb for higher power. Of course, the
> adjustments will interact with the tuner settings for the end-fed wire. But
> the "tuning" of the counterpoise is usually broad enough (low-Q) that noting
> the settings for each band you can return to them without doing the whole
> retuning thing again. (The MFJ box my buddy bought has an ammeter built in.)
>
>
> My "counterpoise" was a thin white wire run around the baseboard of the
> shack and down the hall - about 30 feet total. White wire + apartment white
> wall = invisible counterpoise. Worked FB 40 through 10 meters.
>
> While that will reduce the RF voltage on the rig itself, you will be sitting
> in a high-level RF field from the end fed wire, which limits your maximum
> power to meet radiation exposure limits, depending upon how far from you the
> antenna is located and the band you are using.
>
> 73, Ron AC7AC
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