J-4024/U GRC-206 Interconnecting Box

© Brooke Clarke 2013

Shipping Damage


This interconnecting box (modem) allows a teletype (TTY) to be connected to the GRC-206 system.  Since the system is typically used with two operators (Air Force and Army) there is provision to connect the TTY to either side of the system.

I've heard that this was used in the GRC-122 and GRC-142 HF radio TTY shelters.  Now the question is was it really used in the GRC-206?

Shipping Damage

J-4024/U GRC-206 Interconnecting Box Shipping
J-4024/U GRC-206 Interconnecting Box Shipping

The unit arrived in a cardboard box with more than one seam ripped open and a USPS tape talking about missing contents.  There was no bubble wrap or other packing material.
This resulted in damage.  The obvious damage is to the banana jacks for the TTY and one of the switches does not turn and some of the fuses are loose.  There's probably hidden damage.  This is a real shame since this is not a common item.



J-4024/U GRC-206 Interconnecting Box Shipping
                  Damage J-4024/U GRC-206 Interconnecting Box Shipping


Transmitter: 1 or 2
Home Copy: Rec1, Off, or Rec 2
Power: On or Off (green pilot light for On)
Fuses: F1 1/2A, F2 1/2A, F3 3A
Spare Fuses: one each 1/2A and 3A


Power Source: 115 VAC or 230 VAC or 28 VDC

J1: Black DLED (Dedicated Loop Encryption Device) clear text
J2: Red DLED (Dedicated Loop Encryption Device) cypher text
J3: AC Power In
J4: DLED Power
J5: Red Transmitter TTY1
J6: Red Transmitter TTY2
J7: Red Receiver TTY1
J8: Red Receiver TTY2
J9: ?
J10: ?
J11: DC Power In

Modem (banana jacks)
L1 (Black) & L2 (Red): Modem Send loop
L3 (White) & L4 (Blue): Modem Rec loop

Marking lower right: 81 LOT 9298

The interior of the box is divided into 3 sections:
Top: Red transmission and reception
Middle: Power supplies including a 250 volt loop supply
Bottom: Black transmission and reception.


GRC-206 on PRC-104 web page
MT-6250 Mount for the GRC-206 with a lot of details an list of the GRC-206 components
RT-1319/PRC-113 man portable AM VHF & UHF aircraft radio


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page created 6 June 2013.