[GreenKeys] AN/GRC-122B with MK-2488/G

Sun, 29 Feb 2004 11:31:56 -0800

Hi. I'm restoring an AN/GRC-122B RTTY set, mounted on the back of my
HMMWV:

    http://www.qsl.net/ke6myk/greentruck/truck2/mods.html#shelter

The AN/GRC-122B has one AN/GRC-106 transceiver, a second
receiver-exciter for duplex reception, and MD-522A modem, a PP-4763A
power supply, two TT-98 TTYs, and one TT-76 punch/reader, plus various
junction boxes, inverters, etc, all mounted in an S-250/G shelter.

My set has Modification Kit MK-2488/G, which removes the original
KW-7 crypto gear and/or dummy boxes, changes some cabling, and adds a
J-4024/U junction box to allow a KG-84 Digital Line Encryption Device
(DLED) to be used. Of course, my set does not include the KG-84.

I just got the power amplifier to intermittently work, so I tried to
check in to the west coast mil radio collectors' group net last night,
but I didn't hear the net. I'll try to check into the wednesday
ArmyRadios net with it if I get home from work in time. I haven't
checked into either net for many weeks, because I haven't had anything
new to say, so I don't know if either of them has moved since the last
time I checked in. It's been my experience that the periodic net
posting on the ArmyRadios list is often (usually?) out of sync with
what the nets are actually doing.

I haven't gotten the TTY loops to work yet. Should the system work
normally in clear-text mode with the DLED not plugged in, or will I
have to do something to it (i.e., make dummy plugs to replace the
DLED, disconnect the J-4024/U from the system and go back to
pre-MK-2488 configuration, etc)?

One discrepancy that I've noticed so far between my cabling diagrams
and my set is that my set has a cable between the modem's loop 1 plug
and the banana plugs on the back of the J-4024/U, while the diagrams
show that the modem's loop 1 plug and the J-4024/U both connect to the
SA-1650 switch box (i.e., the J-4024/U connects to one of the phone
jacks on the front of the switch box). I have a spare pile of cables
from another shelter, so I could wire my system up either way.

At some time in the future, I may consider replacing the mechanical
TTYs in my set with a pair of AN?UGC-74B TTYs that I have. In case I
decide to do that, does anybody out there have an AN/GRC-122E
dataplate (for the outside of the shelter door) that they'd like to
part with? Technically, the power panel should be replaced with a
different type, too, but that would take a lot more work! :-)

I also need a set of meters for the PP-4763A power supply in my
shelter. All of the meters were removed. I've managed to dig up
original meters for everything else other than the power panel, and I
substituted some off-the-shelf voltage meters from the local
electronics shop there.

I'd appreciate any suggestions on how to deal with the TTY loops in my
set. Thanks in advance!

--
Mark J. Blair, NF6X <[email protected]>
PGP 2.6.2 public key available from http://www.keyserver.net/
Web page: http://www.qsl.net/ke6myk/