[Johnson] Johnson KW Matchbox on 160 meters

Wed, 26 Feb 2003 20:55:31 -0500

Unfortunately...

Open the box and look at the caps and coil. Double the physical size
of both caps. Double the size of the coil.

That's why tuners that really cover 160 meters are expensive and/or
large.

You can switch in additional capacity to use the same coil. But the
ratio will be off, too much circulating current, and the efficiency
will suffer badly. A recent article in QST laid out the efficiencies
of current tuners. Look how few make the mark cleanly on 160m (one).
Some tuners don't even pass half the power on 160.

You might do better to feed both sides of the feedline shorted
together for 160m use. If you're lucky the 80 m dipole ends (as a
tophat) and the length of the feedline (as the radiator) will be
closer to an electrical 1/2 wave than a 1/4 wave on 160, and you can
use a parallel tuned circuit and a tap on the coil to feed it against
ground.

Particularly from the days when almost everyone had open wire or
ladder line feeding a doublet or "windom", using both sides of the
feedline as a radiator has been an effective antenna for 160 or 80.

The rub is that you have to roll your own matching network. Or the
feedline may not be long enough. If you have 100+ feet of ladderline
you can probably make it work.

73, Guy.

----- Original Message -----
From: "Steve" <[email protected]>
To: <[email protected]>
Sent: Wednesday, February 26, 2003 6:32 PM
Subject: [Johnson] Johnson KW Matchbox on 160 meters

> Does anyone know of a modification for the KW Matchbox that would
allow
> it to operate on 160 meters?
>
> I ran into a ham recently who suggested that such a modification has
> been published but could not recall when or what the details might
be.
>
> I feed 80 and 40 meter dipoles on a common center insulator with
open
> wire.  Would like to use them on 160 with the KW Matchbox.  Any
chance?
>
> Thanks.
> Steve
> K8JQ
>
>
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