[TMC] Odd plug-in on FFR receiver

[Nick England]

Here's a 1967 photo at the NAVCOMMSTA Iceland receiver site
http://www.navy-radio.com/commsta/iceland/iceland-jd-1705-09.jpg
Three of the FFR receivers (AN/FRR-49) have a very odd "something" where
the tuning unit plugs in. What the heck is that? Maybe an add-on crystal
oven?

FWIW More 1967 photos here -
http://www.navy-radio.com/commsta/iceland.htm#jd

Cheers,
Nick England K4NYW
www.navy-radio.com