[Milsurplus] GRC-109 variant ?

[Don Reaves W5OR]

Robert said,

> a Coder Burst Transmission Group.  I can't guess what 
> "MWO-39" would refer to.

Per Pete McCollum at http://www.militaryradio.com/spyradio/rs1.html

Many RT-3's have a marking on the panel that reads "MWO 39". This was
apparently a Modification Work Order by the Army to add a pair of
back-to-back germanium diodes connected between the receiver antenna
connection and ground, thus making it the same as a T-784/GRC-109 (which
has the diodes in the standard design). The unmodified RT-3 does not
have the diodes, but rather is shipped with a jumper wire installed
between the "RCVR" binding post and "GND". According to the RS-1 manual,
the purpose of the jumper is to allow the key-click filter to work
correctly when the RT-3 and RR-2 are not sharing the same antenna. The
manual also mentions that using an external key can cause high RF
voltages to appear on the "RCVR" connection, because of the loop
impedance of the extra wiring. These RF voltages can be high enough to
cause damage to the receiver. So, adding the diodes solves two problems:
it eliminates the need for the jumper wire when the RT-3 has it's own
antenna; and it acts to protect the receiver when an external key is
being used.

 
Don 
w5or@comcast.net