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[TowerTalk] Murch Tuner Question

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Subject: [TowerTalk] Murch Tuner Question
From: (Marty Tippin)
Date: Thu, 25 Jun 1998 08:55:20 -0500
I know it's not tower-related, but there's a lot of smart fellas here
who may be able to help...

I've got a Murch UT-2000A - works great; can match just about anything.
Only problem is, there's no way to bypass the tuner without one or more
external antenna switches.

So I tried to rig up an internal bypass switch using a DPDT switch with
a ceramic wafer.  The input coax is switched to either the tuning
capacitor as normal or shorted directly to the output coax, which is
similarly switched between the other tuning cap and the input. For runs
to/from the switch, I used RG-8 with the shield grounded to the case,
and the switch mounted in the front panel of the tuner. 

Something isn't right, though - when I put the switch in "bypass" and
run to a 50-ohm dummy load, the SWR is 1.8:1 or so.  Apparently there's
some kind of interaction going on in the switch or coax runs - I removed
the switch from the panel and saw no change.  Re-routed all coax runs to
be as far from the other components as possible (like outside the case),
no change.  Disconnected everything except the switch and the lead from
input to switch and from switch to output, still no change.  Stripped
the shield off of the coax, still no change.

So I'm stumped - only guess is that there's something wrong with the
switch.  Checked for continuity between all inputs and outputs and
nothing was awry there.

Any ideas how I should wire this thing up so I can bypass the tuner?
Maybe I need a different kind of switch - suggestions?


-Marty KI0LO

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