AN/URM-90 Impedance Bridge Questions

Rob Dunn dunnr at IX.NETCOM.COM
Wed Jul 28 15:38:16 EDT 1999

Hi All,

First I would like to say thank you to all who provided me with insight into
the R-174 that I acquired this weekend.  Special thanks to Tom Norris who
sent me a scanned schematic of the radio and power supply.  I have traced
out the hombrew supply and it parallels the original in function if not in
design (uses a sand-state power transistor as a series pass filiment voltage

Secondly I have what appears to be an even tougher question.  Along with the
R-174 I picked up one each USM-116A and USM-116B VTVM's with RF probes and
one had the basic docs with it so I have a schematic, etc.  Hopefully these
will work as well as a a HP-410B/C for boatanchor work.  I also acquired an
AN/URM-90 Impedence Bridge (along with a mine detector, radiac meter, vacuum
pump, etc).  I looks like a great bridge and appears to be healthy but I
don't have any documentation for it.  A search of the net only results in a
couple of hits and only one manual site, W7FG.  W7FG's web site is down so I
have no source of a manual.  Does anybody have any information/experience
with the URM-90 and/or know how I can get a manual?

As always, thank you in advance for your help.

Rob Dunn

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