Brief Overview. 6/11/17
See TM11-5820-489-10 (Operators Manual) for details.
The Control Group AN/GRA-6 Radio Wire Integration (RWI) system enables a remotely located soldier carrying a radio to communicate with a distant subscriber on a field telephone system. Or vice-versa, using this equipment as a “phone patch”.
It is very much an early, battle-tested, simplex “cellular telephone” system. The high powered radio, often in a vehicle, with its efficient antenna and robust power source can be located on favorable (high/controlled) terrain feature to greatly extend the radio range. The “GRA-6” then connects that radio with the wired field telephone system.
The AN/GRA-6 system got its first combat test during the Korean War and was certainly used in Vietnam. By the Korean War, it had largely replaced earlier WWII RWI sets that operated with both AM and FM tactical radio circuits. Those systems included the RM-29/39, RC-261 and others.
When the “New Family” of VRC-12 equipment entered service in the mid-1960’s, the AN/GRA-6 system was replaced by the AN/GRA-39 which provides the same function in those newer systems. RWI is now known as NRI, Net Radio Interface.
(Note that the GRA-6 RWI set can also be used with the “new family” VRC-12 series equipment. For example, the radio could be an AN/PRC-25 and it is connected to the C-434 Local control box via the Cable Assembly, Special Purpose CX-7474/U cable. This cable has a “new family” connector on one end and an “old family” connector on the other.)
Above: The C-434 Local Control (left) and C-433 Remote Control (right) here connected with 150 feet of WD-1A/TT infantry field telephone wire for testing purposes. Cables at the rear of the Local unit plug into the radio(s) to be controlled remotely (not seen above). The Local Control unit can also be directly plugged into the MT-297/8 shock mount supporting the GRC-3/8 sets while installed in a vehicle. In that installation the distant Remote Control unit can select either of the installed radios as needed.
NOTE: In this system “Local” means local to the radio set. “Remote” means distant from the actual radio set being used.
Above: The C-434 Local Control set seen here sitting on the seat underneath the A.R.C. Type 12 Aircraft set (which is not involved). The VRC-7 radio, (AKA the RT-70 as the Receiver-Transmitter), is mounted in the vehicle using its battery and antenna system. The C-434 plugs into the handset jack on the radio for remote control operation. The GRA-6 system will also work with the other “Old Family” radios such as the GRC-3/8, PRC-10 and PRC-47 etc.
Below is the other end of the field RWI set in camp, here controlling the VRC-7 VHF FM set mounted in the truck parked at an advantageous location. The Remote Control C-433 system shown below on the left permits remote operation of “Old Family” tactical equipment over infantry field telephone wire. The remote set may be up to 2 miles away from the controlled radio. (That AN/TRC-77 HF CW set was also located at this field site but not connected to the RWI system.)
Above: The GRA-6 Remote Control set, C-433/GRC seen here on the left, can also provide power ON/OFF functioning of the remote radio(s). In the TEL mode, it functions as a normal duplex sound powered field telephone (both handsets keyed) with the Local Control at the radio location. The addition of the J-654/G Audio Junction Box plugged into either Control set enables the use of a handset and external LS-166 speaker simultaneously.
Although this system uses sound-powered voice circuits, each unit contains two BA-30 (D Cell) batteries to bias the carbon microphone elements in each H-33/PT Handset. The Remote unit also uses a BA-414/U 45 volt battery to send switching current down the line to actuate relays in the Local unit for the purpose of controlling the power to the radio (if needed). Nine volt batteries in series (the number depending upon the wire length) can provide that voltage absent a 45 volt battery.
Above: Meanwhile down in the Commo Bunker. The AN/VRC-10 (RT-68 Receiver-Transmitter) being remotely controlled by the AN/GRA-6 RWI system. Run that commo wire out to your distant OP or TOC.
This system can also be integrated into a larger area field telephone system via standard field switchboards such as the SB-22. This enables any telephone subscriber to connect to distant units via telephone/radio.
The GRA-6 system works great; the sound quality on both transmit and receive is very good. It was well designed and very handy as a “phone patch”.
“That’s right – pepperoni, bell peppers, no anchovies. When can you get here?“