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(c) 1999,2008 Peter McCollum

 The GRC-109 HF Transceiver

[See the RS-1 section for other technical details.]

The GRC-109 is the Army adoption of the RS-1, and consists of receiver R-1004, transmitter T-784, and power supply PP-2685 or PP-2684. The RS-1 and GRC-109 are identical except for labeling, although all known T-784's have a connector for a Burst Coder (GRA-71) on the front panel. This difference is an "MWO" (Modification Work Order) on the T-784. Other than the burst-coder connector and the markings, the GRC-109 is virtually identical to the RS-1.

The T-784 characteristics are described in NSN 5820-00-892-0880. Original cost: $532. The R-1004 characteristics are described in NSN 5820-00-892-0882. Original cost: $1122. The units are waterproofed and tested for 7.5 PSI.

There is also a GRC-109A set, which is a later model and has a different case with hasp-type lid fasteners, instead of thumbscrews; and there is a carrying handle built into one side. It also has some cost-saving design changes: for example, the window for the tuning dial is a part of the front-panel casting, instead of being a separate screw-on piece. The "A" model is probably more rugged, due to the thicker case and heavier construction, but it is 'less attractive' than the earlier model. The CIA did not have an equivalent to the GRC-109A, and production of the RS-1 had probably stopped several years before.

A GRC-109 set in use in the field, from a picture in the manual. See the RS-1 section for close-ups of the receiver and transmitter.

 

AN/GRC-109 Radio Station Specifications

 

 

 

 

Receiver R-1004

Transmitter T-784

Power Supply PP-2684 and PP-2685

Weight

10 lbs

9 lbs

PP-2684: 24 1/2 lbs

PP-2685: 12 lbs

Dimensions

8-5/8" X 5-1/2" X 5-7/16"

8-5/8" X 5-1/2" X 5-7/16"

PP-2684: 10" X 8-1/2" X 5-1/2"

PP-2685: 8-5/8" X 5-1/2" X 5-7/16"

Tube complement

1T4 RF amp

6AC7 oscillator

0B2 regulator

 

1L6 converter

2E26 final

 

 

1T4 IF amp (two)

 

 

 

1U5 detector/audio

 

 

 

1T4 BFO/audio

 

 

Frequency Bands

3-6, 6-12, 12-24 MC

3-5.5, 6-9, 10-16, 17-22 MC

 

Power Output

30 mW into 4K ohms

12-15 W, 3-15 MC

10-12 W, 15-22 MC

 

 

GRC-109 sets with hand-crank generators, part of a static display in Germany in 1959. Image courtesy of Rocky Lewis (the gentleman in the picture).

 

The "A-model" receiver, an R-1004A/GRC-109A serial 141A. Note the lid fastener latches, and the tuning dial window that is integral with the front panel. Internal components appear to be identical to the R-1004.

Admiral Corporation apparently made all of the GRC-109 equipment (and most of the RS-1's), and Oklahoma Aerotronics made all of the GRC-109A's. The "A" models all have an A-suffix on the serial number, and they have snap-type lid fasteners instead of thumbscrews.

All (?) T-784's have been modified as per "MWO 11-5820-474-35/1", which is described in the GRA-71 manual as: "Modification of Radio Set AN/GRC-109 to make it compatible with Coder - Burst Transmission Group AN/GRA-71". Presumably, this MWO was to install the connector on the T-784 that mates with the GRA-71. The "A" models have the burst-coder connector without the need for the MWO. Some (all?) R-1004A's have the word "receiver" spelled incorrectly on the lid's ID plate (they spelled it "reciever").

 

A PP-2684/GRC-109 power supply. It is identical to the RP-1 except for the ID plate. It accepts either AC input, or 6 volts DC from a storage battery, or several voltages from a hand-crank generator (using the capped connector in the lower-right). Author's collection.

 

A PP-2685/GRC-109 power supply. It is identical to the RP-2 except for the ID plate. It accepts AC voltage input only. The cap in the lower-right is for access to the 0B2 regulator tube. Author's collection.

 

The CY-4321/GRC-109 Maintenance Kit. It contains spare tubes, a vibrator, fuses, antenna insulators, tools, etc. Earlier examples are unmarked (as are probably all boxes shipped with CIA RS-1 sets). Author's collection.

Another power supply option for the GRC-109 was the UGP-12 gas generator. It is a 2-stroke engine that provided 115 VAC 400 Hz 125 watts. The UGP-12 is mentioned on page 9 of the GRC-109 manual. Click here for a picture (photo courtesy of Pasquale Lombardi).

Yet another, probably later power supply option is the PA-109, a switching-type supply for operation from 12 VDC. It does not have military markings, but is clearly intended to operate the GRC-109 set or it’s equivalent.

A “Power Adaptor PA-109”, for operation from 12 VDC. Since the switch is labeled “XMTR PWR”, perhaps the receiver power is available at all times? Note that the lid thumbscrews and the power connectors are extremely similar to the GRC-109. The unit’s weight is about 2 pounds. Image courtesy of Tony Grogan.

The data plate from a PA-109. Image courtesy of Tony Grogan.

 

History of the GRC-109

[See the similar historical information under the RS-1 section.]

The GRC-109 started production about 1961. Compared to the RS-1, GRC-109 units have more date-coded components, and more documentation is available to support those dates. GRC-109A units have a 1969 contract date on the ID plate.

In late 1961, the CIA organized a number of 12-man Special Forces teams to work with Montagnard tribesmen, and used the RS-1 for communications. Meanwhile, the Army's chief signal officer arranged for the RS-1 to be adopted for military use and renamed the GRC-109. Even though the Army had many RS-1 sets in use already, giving it an Army identifier would have simplified logistics. By late 1962, the Special Forces team network had 24 stations. The GRC-109 set in each "A detachment" SF camp was kept in a sandbagged bunker, with several antennas installed. The antennas were a target of Viet Cong raids, but for emergencies, they found that a longwire buried 18" underground in bamboo pipes could be used. [Ref. 6]

The GRC-109 became a standard issue radio to all combat units in forward areas after 1965. It was included in the inventory of all fire bases, and was at least used as a backup radio. Even though Special Forces had access to the latest high-tech radios, by the mid-1970's many units had adopted the GRC-109 as their primary long-range radio. It was rugged, reliable, and maintainable in the field, and offered several power supply options. The newer radios tended to require specialized batteries which were often not available in the field.

Estimated dates are summarized as follows:

GRC-109 notes from John Liner:

[Regarding reliability:] I never had a 109 fail to function. I was always able to communicate and send my traffic through with it. I operated in many different locations, including an A camp in Viet Nam, the forests in southern Germany, and out of apartment buildings in downtown West Berlin.

[Regarding the apartment building use:] I used the big power supply that is part of the GRC-109 kit [PP-2684]. The antenna was a broomstick with about 50-75 feet of wire wound on it, with another 10 feet trailing off the end. The coil of wire sort of made the antenna look electrically longer. I placed the broomstick in a window and let the wire dangle out of it. Other guys have used stairwell banisters for antennas. For a ground I just ran a wire to the radiator in the room (most old German pre-war apartments had steam heat).

GRC-109 notes from Don Valentine:

We had small dry batteries for the AN/GRC-109 receiver so we wouldn't have to crank that %$#@%$# generator to send and receive messages. I never saw a PA-109 while I was in SF. Apparently, it was only for transmitting and the operator had to have a dry cell battery for the receiver or have the team gorilla crank that &%$@#$ generator.

The 109 was very forgiving if you didn't erect a by-the-book antenna. When in Laos, I communicated from Luang Prabang to Vietiane using a coat hanger. It would even load a military vehicle, wire clothes line, or barbwire fence and use that for an antenna.

The AN/PRC-74 replaced the GRC-109 on the SFODs in the mid-60s, except for the A Camps in Vietnam. We helped test the proto-types while we were assigned to Project Delta [Det. B-52, 5th SFGA] in Vietnam. The proto-types were called HC-162s.

 

Image courtesy of Rick Larson.

Pictured above is an antenna device that was perhaps intended to be used with the GRC-109. Details from Rick Larson:

“It was intended to be fired in an M79 grenade launcher. The projectile is a black anodized aluminum cylinder filled with green plastic insulated antenna wire that pays out in flight. One end of the wire was attached to the heavy steel cartridge case and the other in the projectile. When the cartridge is fired, the projectile was supposed to penetrate through the jungle canopy and leave the wire hanging in the treetops. The other end remained attached to the fired case, and when unloaded from the M79, could be cut off and attached to the radio.
I've seen three of these over the years and the one in my collection is marked (in felt pen) for SEAL and SF use with GRC-103 radio. I believe this is incorrect and was actually intended for the GRC-109. One example I've examined was a cutaway that came from the manufacturer, AAI Corp., via a retired engineer. The other was at the EOD unit at Camp Pendelton about 20 years ago.”

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