[TowerTalk] Murch Tuner Question

[Marty Tippin]

Something I forgot to mention:  The dummy load is working fine - 1:1 SWR
without the tuner in the circuit.  I've tried two different dummy loads
with the same results.

-Marty
> -----Original Message-----
> From:	Marty Tippin 
> Sent:	Thursday, June 25, 1998 8:55 AM
> To:	'towertalk@contesting.com'
> Subject:	[TowerTalk] Murch Tuner Question
> 
> 
> 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?
> 
> Thanks,
> 
> -Marty KI0LO
>  martyt@pobox.com
> 

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