operating frequencies. Doing so causes high current in the radials and you
> John, as a general rule I try to get at least 1/4 wavelength of radiator
> up.
> That's not always practical but it's worth striving for since below 1/4
> wavelength the feed point impedance and so the efficiency drops very
> quickly.
>
> If you are working against a counterpoise, something close to 1/2 wave is
> ideal since it raises the impedance is highest at the length. However, the
> impedance can easily rise above that which the tuner can match.
>
> An easy way to adjust the length of the antenna is to loop the wire through
> an insulator that is up as high as possible (at times I have used some
> monofilament fishing line with a loop through which the loop of lightweight
> antenna wire passed). Now, depending upon the amount of sag allowed, I can
> adjust the length by simply letting out or pulling in the radiator wire.
> The
> RF sees the folded back-wire as simply a thicker single wire since the RF
> field passes over wire, not through it. That adjustment is often enough to
> move the feed point impedance to something the tuner can handle.
>
> A 1/4 wavelength counterpoise is ideal since it minimizes the RF voltage at
> the rig. For that reason, it's good to avoid 1/2 wavelength counterpoise
> since that puts a voltage maximum at the rig.
>
> A "random wire" antenna like this with one "counterpoise" wire is really
> just an off center fed radiator. The counterpoise and radiator are one RF
> circuit. The advantage is you only need one elevated point. The
> disadvantage
> is that the counterpoise also radiates but it only "warms the worms" Hi!
> So,
> whenever possible I try to get both wires up into the air with at least a
> 90-degree angle between them (so the RF fields won't tend to cancel each
> other) even though one wire might be a lot longer than the other.
>
> Ron AC7AC
>
>
>
> -----Original Message-----
> From:
[hidden email]
> [mailto:
[hidden email]] On Behalf Of John Shadle
> Sent: Friday, June 17, 2011 7:20 AM
> To:
[hidden email]
> Subject: [Elecraft] [K2] wire antenna lengths for portable operations
>
> I'm headed up to KL7-land next week and am going to take the K2 with
> me. I was thinking about using the KAT2 to tune a wire attached to the
> BL2 (at the 1:1 setting).
>
> Probably going to cut some teflon-coated wire this evening and pack it
> away in the bag.
>
> I'm seeking input on the best lengths of wire to cut for the active
> part of the antenna as well as the counterpoise.
>
> If you have any other comments on this setup, I'd love to hear them,
> too. In the past, I've used the K2 attached to my homebrew vertical
> (SGC SG-239 at the base of a elevated ground plane vertical), so this
> is my first adventure with "random wire" antennas.
>
> Thanks!
> -john W4PAH
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