[R-390] R-391/URR (MOD) - Direction Finder Set AN/FRA-44 --- Receiving Set AN/FLR-7

[Clay Curtiss WA7KBR]

Hi,
I'm new to the list and looking for some advice on an R-391 (S/N 145) that I
have.  It was an original 1951 Collins unit (contract 14214-PH-51-93) and
was modifed by RCA for the Navy and has an additional 3"x2"metal tag on the
front panel below the function switch.  It reads as follows:

R-391/URR (MOD)
RECEIVER, RADIO
-------------------------------------------------------------------------
A UNIT OF DIRECTION FINDER SET AN/FRA-44 (XN-1)
COUNTER MEASURES RECEIVING SET AN/FLR-7 (XN-1)
-------------------------------------------------------------------------
MODIFIED FOR
NAVY DEPARTMENT - BUREAU OF SHIPS
BY CONTRACTOR
RADIO CORPORATION OF AMERICA
CAMDEN, NJ
CONTRACT NObsr 81315
US

I've searched this list's archives, but find no mention of it.  I tried
google and came up with a reference to Antenna AN/FLR-7 on www.r-390a.net in
the FAQ as follows:

This Wullenweber antenna, also known as a Circularly Disposed Antenna Array
(CDAA), consisted of a large number of 200 foot towers arranged into a ring
more
than 1300 feet in diameter.  An inner ring of shorter towers competed the
array.
The antenna reportedly operated from VLF well into the VHF frequency range.
It
provided direction finding accuracy to within two or three degrees,
according to
some reports.

When I first got it, it worked but always had ringing in the audio.  I
suppose it could have been modified to have a very narrow IF bandpass.

Does anyone have any info on how this R-391 was modified by RCA?  I suspect
that there weren't very many of these made, and I don't know if it is rare
enough or interesting enough for anyone to care about.  Would it be best to
leave a unit like this in it's current configuration, or to try to convert
it back to a stock R-391 again?


Thanks for any and all help.

Clay
WA7KBR