AN/GRC-109 Special Forces radio set
The AN/GRC-109 Special Forces radio set consists of the R-1004 receiver, the T-784 Transmitter and two power supplies, the smaller PP-2685 for AC input of a variety of voltages from 75 to 260 volts, and the larger PP-2684 for 6 volts DC as well as the same variety of AC voltages. The set came with a 5820-00-788-5496 Maintenance Kit (a spares kit with fuses, tubes and other spares, as well as tools and some accessories.)
As used by the CIA The AN/GRC-109 is a relabeled copy of the RS-1 set designed for use by the Central Intelligence Agency (CIA) as a clandestine radio set. The RS-1 was designed in the late 1940s and used by the CIA in various undercover locations such as Eastern Europe, Cuba, and Asia for a reported 12 to 15 years. Not only could it be used with a variety of input voltages, but it was capable of loading nearly any antenna. The set was designed to be modular so that the receiver, transmitter, and power supply could be separately handled and hidden as smaller packages. Each piece with its cover in place was designed to be waterproofed to about 7.5 psi pressure and could be directly buried in the ground for later use or retrieval. A special dessicant tube with rechargeable dessicant granules was screwed into the side of each case to remove internal moisture. All of the control bushings use a neoprene gasket material that maintains waterproofing while still allowing easy turning of the knobs.
Adopted for use by Special Forces The CIA set up special teams to work directly with the Montagnard tribesmen in Vietnam in the early 1960s. The RS-1 set was used initially. The Army's chief signal officer ordered identical sets made with the military designation of AN/GRC-109. Both the RS-1 and the GRC-109 were made by the Admiral Corporation. Later during the Vietnam War, the GRC-109 was used extensively in forward areas.
This set arrived at my QTH with nearly all the spares and in the original boxes as tested and overhauled by the Tobyhanna Depot in the 1980s. Special thanks go to Chuck M. for practically giving me this set. When first contacted, I had no idea the set would be as clean and complete as this one turned out to be.
Repairs
Other than some cleaning and testing, this set needed nothing. I thoroughly inspected and tested each of the pieces.The quality of construction for the components is very evident. They were built as if men's lives would be dependent on the ruggedness, versatility, and ease of use. The only problem I found was solved by applying a bit of deoxit to the contacts under the "crystal oscillator" cover on the receiver. The "crystal oscillator" connection allows the receiver to be crystal controlled with a crystal that is 455 KHz higher than the receive frequency. With no receive crystal inside, the internal connections need to be maintained.
R-1004/ GRC-109 receiver chassis.
The R-1004 receiver is a single conversion superhet with an IF frequency of 455 KHz, manual RF gain (but no AGC), BFO, one stage of RF and two stages of IF amplification. The audio output is designed for 4000 ohm headphones but can handle a speaker with a proper matching transformer. The circuit reminds me of a Zenith Transoceanic with battery miniature tubes but adding voltage regulation, a second stage of IF, a BFO and with precision in construction that is reminiscent of a WW II frequency meter. Tubes are 1U5 as audio amplifier, 1L6 as converter, and four 1T4 with one used as RF amp, two as IF amp, and one for BFO. Frequency coverage is from 3 to 24 MHz in three bands. Reception is for AM or CW. Power is supplied by either of the standard power supplies or battery.
Bottom of R-1004/ GRC-109 chassis with shields removed.
The T-784 transmitter is crystal controlled for CW (Morse Code) operation with the built-in or external key. Coverage is from 3 to 22 MHz in four bands. A chart on the unit shows recommended initial control settings for the various frequencies. The circuit is a MOPA with 6AC7 as oscillator and 2E26 as RF output. Power output is 10 to 15 watts depending upon frequency. Power requirements are 6 volts for filaments and 450 volts at 100 mA for B+. Neon lamps are used as tuning indicators and a #47 pilot lamp as loading indicator. A connector is provided for an external burst keyer.
T-784/ GRC-109 transmitter chassis. Note brass dessicant cartridge.
T-784/ GRC-109 transmitter chassis.
The power supplies can be switch-selected to operate from nearly any AC line voltage in the world. AC input is from 75 to 260 volts at 40 to 400 Hertz.
Testing the PP-2684/ GRC-109 power supply (ser #190) at no load.
AC power plug and adapters.
Performance The receiver's lack of AGC and relative wide receive bandwidth limits its performance to some extent on the ham bands. It also easily overloads with a strong nearby signal. However, it is very stable and is a delight for shortwave listening. The transmitter is very usable on the ham bands. If both are used together on the same frequency, an external switching arrangement that shorts the antenna input to the receiver during transmission and opens it to the transmitter during receive is necessary. I am assuming that for use in theater, separate receive and transmission frequencies were used.
Eric WD8RIF borrowed the transmitter for the 2011 ARRL Straight Key night. His report can be found at this link.
More information
Here is a link to a Google book that describes the use of the RS-1 and GRC-109 for reliable distance communications
in Vietnam.
An underground long-wire antenna in a bamboo pipe buried 18 inches underground? Apparently it worked as an emergency antenna according to the original sources referenced in this book!
Peter McCollum has an excellent web site on spy radios. Here's his page on the GRC-109 complete with several pictures of the set in use in Southeast Asia.
For more historical information and the use of the set for ham purposes see this page by Dave VA3ORP .
Tim N6CC has a simple solution for hooking a VFO to one of these. His full website has lots of other good info.
The Technical Manual for the GRC-109 is TM 11-5820-474-14 and is available from BAMA at this link.
Your story? If you used the GRC-109 (or the RS-1) in theater, share your story and any pictures you might have of the equipment in actual use. See my BA Pix home page for e-mail address. And thanks for your service.
Responding to my request, Dave KD4WR wrote on my guestbook about his training experienes in SF (Special Forces):
- Reference the AN/GRC 109
SF Radio.
I was in SF right at the end of the Vietnam War and did my training in winter-spring of 1973. Students were assigned to all the positions of an Operational Detachment (A-Team) depending on their occupational specialty. I was the team medic but being a Ham, I took special interest in the radio gear. We used the set type that you show on your website. Two pieces of equipment that we used, were the "coder/burster device" I forget it's designation and the infernal hand-driven generator. An aluminum affair with a stool type bicycle-like seat attached to an enclosed circular disk (containing the generator) with bicycle pedal handles on each side of the disk. Memories fade so the description might not be accurate, but I will never forget those nights when it was my turn to operate the generator! Everybody took a turn. No batteries, to my recollection- the generator was the only power we were allowed to use. The generator was air dropable attached to a single jumper and the rest of the set was divided among the team when we jumped into an operation. More on the way we used the system, if you are interested.
"Hi Dave, Of course I am interested. Did you use the equipment in theater or was this training for a possible?
The code-burst attachment connector is unique to the 109 and was not part of the earlier CIA version to my knowledge. It was a compact solid state thing that plugged into the transmitter so as to limit the time needed on the air to avoid direction-find detection.
Hello Rich,
Thanks for your response. Unfortunately, I remember very little about the antenna and feed line. We all were trained on how to cut a wire to frequency and set up an long-wire antenna, presumably to be used for this radio, but I don't remember much about that. What I do remember is the way we used the radio. The classic mission of the Green Beret A-Team is to infiltrate into a country that has a faction or formal government that is hostile to the interests of the US. In order to combat this hostile faction or government, an A-team or multiple A-teams are deployed in country in a clandestine role to advise, train and equip up to 1500 guerilla troops per A-team to bring the situation in line with the interests of the USA. Obviously the team must avoid military contact with all hostile elements in the country but must make and sustain contact with guerillas, key political supporters and operatives from the indigenous population and they must do this without being detected.
Radio communications with command elements/support units, must be handled very carefully. The configuration of the AN/GRC-109 played a key role in maintaining the clandestine nature of the operation. The command element, usually, outside the country of operation, (though not always - Vietnam is primary example), was then called the Joint Unconventional Warfare Task Force (JUWTFA). It included elements of a Special Forces Group Headquarters and any other elements from other service branches. (That's where the "Joint" comes from.) The A, by the way stands for Airborne. Early on in Special Ops, this was referred to as the C-Team. In addition to the C-Team, there was the B-Team which contained supply, medical, transport and communications. Later referred to as a Group Support Battalion. Hope I have not bored nor confused you at this point. Focusing in on the B-Team (Combat Support Battalion), there was a Signal Company in it that operated/maintained some really cool radio equipment. Large vans with portable Yagi-type antennas.
A-team communications were two-way but with send and receive at different times and frequencies. Command level radio messages were sent at human CW speed and were called BTB's or Blind Transmission Broadcasts. Each A-Team had a designated Freq. and Date/time for its BTB. All messages were sent encoded via cipher systems and arranged in 5-letter code groups. The A-team radio op. would turn on the receiver just prior to the start of the BTB. He would copy the 5-letter groups then shut down and decode the message manually using the prearranged cipher system and keys.(These were simple-to-use cipher systems with pads of printed characters and an algorithm for translation - WWII methodology).
If the A-team needed to send a message, to the JUWTFA, the process went like this: I believe, but not sure if, messages were taken anytime, but nevertheless, the A-team Radio Op. would take requests for supplies using a coded catalog supply system, he would then include situation reports and any other traffic that was required. Then he would use the same paper-pad cipher system to encode his message into 5-letter code groups. Here's where we used the coder/burster device. I remember that it looked sort of like a "Dymo Home Label Maker" One of those machines that embossed letters into sticky plastic tape. Just like the Dymo, you turned a wheel to the letter you wanted and then squeezed the handle to emboss the letter; only this device somehow delivered the letter to magnetic tape, just like audio recording tape of the day. Then he plugged it into the transmitter, tuned up and in an instant the entire message was sent truly in just a few seconds of on-air time. I don't know if the tape was electrically or mechanically powered but I do remember that it didn't take more than a few seconds to send a really long message!
The signal company on the JUWTFA end had the sophisticated receivers to detect, capture, slow down and copy off the message accurately. Reply communications would occur during the next BTB, usually the next day.
To answer your question, I went through the Special Forces Officer Course to qualify to become an A-team leader. Officers and Enlisted personnel were trained separately at that time. Officers were not allowed to stay in Special Forces. Today, commissioned officers can qualify for Special Forces as their principal branch, and the Army puts everyone together in one course and builds an A-team from scratch. In my opinion, a much better way! . Since I was a Medical Service Officer, I was assigned to the 5th Special Forces Group Combat Support Battalion (B-Team) where I was a medical operations officer. Explaining this would take another discourse on the multiplicity of Green Beret missions. But, No I was not in theater in Vietnam. I stayed at Ft. Bragg and after some really fun stuff in SF, I moved over to the 82nd Airborne Division for a year and then on to other assignments in strictly medical units. Hope this sheds some light on how the AN/GRC-109 was used. BTW we used VHF (AN/PRC-77) for internal Team communications - each team had two of them. Writer's Cramp,
Again glad to hear from you, Rich,
I can take a crack at more questions if you have them.73
Dave, K4DWR
Thank you Dave!
Date 12-4-10, updates 12-15-10, 1-11-11, 7-2-14, 11-19-14
Heathkit test equipment circa 1948-49 consisting of the G-1, C-1, and T-2 were the previous items on the bench.