[TowerTalk] Johnson Matchbox Question

[Tom Hellem]

Rob-
I think you are on to something. My tuner still has the link (primary) coil, but the relay has been removed, and the lone tap is one turn or so from the grounded end, which as you suggest is for a coaxial input according to the schematic.
I am using the Matchbox to tune an 80 meter dipole fed with a roughly 90 foot piece of 450 ohm window line. My VNA indicates the impedance at the tuner end of the line to be 63-j132 on 80 meters, where I seem to have the most trouble getting a perfect match with the tuner. With the cover off I can see that C-2 is maxed on the upper (ungrounded) section. My best match is around 1.5:1 swr, and it gets worse from there depending upon the weather.
Thoughts?


Tom 
K0SN

> On Mar 14, 2022, at 5:13 AM, Rob Atkinson <ranchorobbo at gmail.com> wrote:
> 
> The "link" (that's the larger outer coil) originally had two taps.
> One just one or two turns from the grounded end.  That was the 50 ohm
> unbalanced input.  A second tap was a  few turns over from that.  It
> was for 300 ohm receiving line.  A lot of receivers had terminal
> strips on their back panels for the option of 300 ohm twin lead
> balance line for receiving, in the 1950s and '60s.   A Matchbox that
> doesn't have the link has been extremely modified into something else.
> It can no longer be a link coupled balanced line network.  Which
> brings me to a question:  Are you using your Matchbox for coax, or
> ladder line to your antenna?
> 
> I have one in regular use here with ladder line and a dipole.  It will
> be easier to determine what's going on with it if you get it out of
> its cover and run it in the open so you can see what's going on WRT
> capacitor meshing.  Just unscrew the zillion screws and put the knobs
> back on and connect the feedlines back up and you'll be able to see if
> you are running out of capacitance, or don't have enough etc.
> 
> 73
> Rob
> K5UJ
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