AN/GRC-109 “Special Forces” Radio Set

Probably my favorite radio set.  The “COOL METER” is Pegged on this one! Used extensively from the early 1960′s through the 1970′s and beyond by US military Special Forces worldwide, including  SF “A” Teams, ARVN units operating inside North Vietnam, Navy PTF boats and others in Vietnam, it did the job well.  Extremely rugged and designed for lengthy burial in the ground as part of an equipment cache, these radios have a Cool Factor 36.6 db higher than any plastic RiceBox ever made by KenYaeIc.  They were, and are extremely reliable, fun and quite EMP-proof. GRC-109′s will be operational LOOOONG after those custom LCD displays and proprietary microscopic microprocessors flame out in all those modern RiceBox appliances. Not to mention those modern, Mil-Spec software defined rigs….

Listen in !

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AR

Designed as an “Armyfied” version of the CIA’s previous RS-1 radio set which had been in widespread use in the 1950′s.  They are very similar in appearance and operation.  The Army adopted it (circa 1962) with minor modifications as the AN/GRC-109 to be supportable with standardized training, repair parts and depot maintenance within the Army supply  and logistics system.

With a transmitter output of around 10 watts, a built in key that works well, versatile power supply and a sensitive receiver, they did the job.  In approximately 1969 the Army introduced the AN/GRC-109A, basically the same radio system however the A model had substantially thicker and stronger cases and it included a quick-remove cover with snap closures versus the screw-down types of the basic 109.  The 109A also included the connector for the GRA-71 burst keyer; apparently most or all of the previous 109′s were subsequently modified for this as well.

Below is the CIA’s RT-3, the transmitter of the RS-1 system. Almost identical to the GRC-109 transmitter (T-784/GRC-109 as described above) but note the absence of the connector for the GRA-71 Code Burst Keyer and a different arrangement of the CW key and receive antenna connector posts.  No other “US” markings – I bet that fooled ‘em !

Reference (3) describes the use of the GRC-109 by US Army Special Forces in Vietnam. It states that the GRC-109 apparently was not issued to conventional Line units in that era.  Other references state otherwise.   In those days, typical Line units depended upon easy-to-operate voice radio systems they had available, especially as the CW skills of many RTO’s atrophied along the way. The 109′s were deployed at SF camps and in fortified villages throughout the country as the only means of reliable comms back to HQ in Saigon and between themselves for mutual support.

The GRC-109 / RS-1 was also used by Special Forces world-wide in the 1950′s – 60′s and likely beyond. I have seen a BA-48 battery (also used with the GRC-9) with a date code of May, 1984 although it’s possible it was made under a foreign sales contract to support these radios being used by our allies. – Or not -

Apparently they were reliable and quite successful in the Special Forces networks in Vietnam. Due to their simplicity and all-weather ruggedness, I would assume they were more reliable than the FRC-93 (Collins KWM-2) that SF was beginning to deploy at SF camps.  Especially when you consider that the FRC-93 required AC power and associated generator not to mention the serious environmental protection.  The GRC-109 could use AC or the hand cranked generator thus increasing its dependability in a combat environment.  They were installed in the “commo bunkers” as a basic means of protection and operational security, however when under attack the VC and NVA were good at spotting antennas. The reference states that as a countermeasure the wire antennas were put inside bamboo “pipes” and buried 18 inches underground – and were still effective in communicating. It’s an authoritative reference but I will take it for face value, no mention of freq or operating range was noted. That’s an experiment I will try to duplicate this summer and see for myself. I’m a bit skeptical, especially during the “wet” season there. I have made contacts with mine using only a 1/4 wave wire laying on the ground – that works OK – but that’s a different story.

My GRC-109 field kit below:

Powered by 70-270 VAC, an optional UGP-12 gas fueled generator, 6 VDC from that captured Zil truck battery or a G-43 hand cranked generator, they could be used anywhere.  The receiver could also be powered by itself from a BA-48 battery for those long watches on the Alert Net.  Environmentally tough, they can withstand and operate in lousy weather.  Plugged into an electric lamp socket in that hotel “safe house” via a screw-in adapter, their CW would not  even blink the house lights during those 0242 hours  SITREP transmissions back to base.  It is capable of running the receiver with crystal control – that works very well but the variable tuning works better for casual Ham operation.  The TX of  course is crystal controlled.  Shown below running a coax-fed dipole for TX and a random RX wire launched into a nearby tree with a pine cone for a weight.

Below is a station on the granite, up in the Sierras, tracking and reporting suspicious canoeing activity on Caples Lake in the background.  The off-camera PU-181 rattling away generating AC power and also discouraging mosquitoes.  A great campsite radio when you are well beyond cell-phone or repeater coverage.  You can also use it to get the latest soccer scores from Radio Australia, coordinate your operations with a time-tick from WWV or get a good laugh from Radio Havana Cuba, “Free Territory of the America’s” on the shortwave bands.

The transmitter will load anything, much like the RS-6.  I have powered up dipoles, inverted “L”s,  random wires, a barbed wire fence, the rain gutters on the home QTH (stealth ops) etc.  As seen in these photos, the T-748/GRC-109 included a TX panel connector for a GRA-71 300 WPM burst keyer so you could send your SITREP with a lower probability of detection before you QRT’d and boogied.

The below photo is another favorite campsite further up into the mountains.  Set up next to my cot, it kept me in touch from a place not covered by VHF FM repeaters and probably 40 miles from the nearest cell phone coverage area. My buddies just shake their heads – but then ask me how to go about getting a Ham license….

BTW, that “hot pink” object in the background is an Army Signal Corps VS-17 visual signal panel laying on the rocks.  They are used to mark friendly positions when working with Tactical Air or other friendlies in the area.  We were using it so that late arriving campers to the general area could locate our position exactly from their avenue of approach.  You can see these things in the bush from many miles away although this photo doesn’t seem to capture its brightness. It must be stressing the color filters in my cheap digital camera!

In fact, it caught the attention of an F-5E Tiger II  jet pilot flying out of NAS Fallon Nevada.  He went overhead about 10,000 feet above us; it caught his eye so he banked and took a second look.  He knew something “military” was going on – civilians don’t usually pack and display these panels; he knew exactly what it was.   He made a wide, descending  turn and then roared directly overhead about 500 feet above us in a hard bank, standing on his wing to see what was going on.   We waved.  His F-5E was painted with Soviet camouflage markings and Red Stars – he was part of the “aggressor” training squadron at the Navy’s Top Gun school off to our east.

My buddies were bragging about how many fish they caught (I didn’t catch any as usual) but I caught an F-5E with MY lure !!

Come to think of it, I was running the GRC-109 at the time.  Maybe the J-STARS aircraft controlling the fight from a hundred miles away detected my CW signal and then got an HF DF fix on my position.  Maybe it wasn’t the panel……

So we then waited for the “duty”  C-130 to parachute us a pallet of MRE’s, water, batteries and ammo but nothing showed up. Well, an airstrike didn’t show up either so I guess we called it a draw.

The only apparent operational shortfall of the GRC-109 while used on Recon patrols was their weight, assisted by the heavy GN-58 or G-43 generator (the transmitter and receivers are relatively light).  Although substantially smaller, lighter and easier to pack than its predecessor GRC-9, it was still a bit heavy even though it was probably viewed as the latest state-of-the-art portable radio station at that time.  It would have been interesting to parachute with one of these strapped on (especially with the G-43 generator and seat) but that was apparently routinely done.  They were ultimately replaced by the PRC-74 or PRC-64 depending upon the unit/AOR, but their use continued on throughout the US military.  Clearly, they were heavily utilized by the CIA along with its predecessor, the RS-1.  One reference stated that they were routinely secreted inside the walls of selected apartment buildings in eastern Europe for use by stay-behind personnel in case the neighborhood went further downhill.

The above photo shows my veteran GRC-109 as it might have been stashed under the floor boards in the attic of Der Funkspiel Hotel, on the corner of Lenin Street and Karl Marx Way in Budapest. This was just across the street from the Headquarters of the Soviet “Friends” T-54 Tank Regiment. Circa 1956. The brave Hungarians eventually won THAT battle.

Willing to bet there are many still in eastern Europe, southeast Asia or buried in various other interesting places worldwide.  Someone back at “HQ” still maintains the freqs/times/callsigns/one-time pads and Comm plan in case any of these sets are ever retrieved and activated by OPLAN XYZ.  Hope someone still knows morse code!  All the best agents do, of course…..I have no doubt that these covert rigs will fire right up when needed.

Below is my trusty ’109 operating “tailgate portable”.  That big box of crystals sure makes life easier on the Ham Bands…  This particular setup runs the “small” AC power supply, PP-2685/GRC-109 which is powered by a 300 watt 120 VAC sine-wave inverter installed in the Bronco.  Clean, quite power.  The larger PP-2684 does everything the 2685 does but it can also be powered by a 6 VDC battery; it can also charge that battery.  For field ops requiring light transport, neither AC power supply is used.  In that configuration the GN-58 or G-43 hand cranked generator in conjunction with the CN-690/GRC-109 is used between the TX/RX and the generator.  The CN-690 contains an OB2 VR tube to regulate the RX B+ voltage – and is much lighter and smaller.  The receiver can also be directly powered by a BA-48 battery.

Above is a R-1004/GRC-109 Receiver being powered from a 12 Volt Gel Cell via a DC-DC Converter which solves the “continuous receive” power requirement when in the field. Details on the Converter are in the Design and Engineering post elsewhere on this website.

My set came from Fair Radio. It has obviously seen a lot of operational service, its pretty scuffed up but being indestructible, keeps on going. None of the serial numbers match but some of the units have an interesting pale green lightning bolt stenciled on them. Wonder who that was….One strange problem they have is the receiver is starved for antenna signal when the antenna is routed through the transmitter during “key up”. The key contacts short out the receiver signal to avoid overloading on transmit, but there is something lacking in the design – the only problem I have found. I guess the TX output network loads the antenna circuit too much during key-up. I’ll have to investigate. As a result, I usually run mine with a dipole or inverted L on the transmitter and a random 50 ‘ wire connected directly to the receiver. Works great but takes a little more setup time. The RS-6 set does not have this problem, but it uses a T/R relay to isolate things, the ’109 does not have a relay.

The “GRC-109 A” model uses the “hasp” method for connecting the cast aluminum covers to the radio chassis. Very strong but very heavy and it makes each chassis quite a bit bigger – I prefer the thumbscrew hold-downs of my plain ’109 better. They also fit inside an ALICE pack better.

A few “features” are noted.  The transmitter antenna output tuning indicator is a #47 lamp across a 20 ohm resistor, this in series with the output to the antenna connector.  This is really an RF current monitor since it is in series.  With antennas with high impedance input, there is little if any glow from this lamp although RF power is being delivered to the antenna.  A 1/2 wavelength (or integer multiple) wire is an example – it may seem like you can’t tune it.  To solve this, I carry an NE-51 neon lamp with leads soldered to it; I then place this from the antenna connector to ground, thus serving as an RF voltage monitor since the transmitter is developing a high voltage in this situation.  This will glow brightly with the above antenna since the input to a 1/2 wave wire is high impedance.  I also use this trick on my SCR-284 transmitter as well.  Handy.  With low impedance antennas (like a dipole or a 1/4 wave wire) the installed #47 glows brightly when tuned.

In the receive department, the R-1004 does not have a AVC/AGC circuit so you may have to ride the “Gain” control in the presence of strong signals.  I have not found this to be a problem when operating up in the mountains – few really strong signals to contend with (no locals !).  However, the set does not incorporate a means to generate a sidetone signal so you can’t hear your own keying very effectively.  Since the receiver does not effectively “mute” during key-down (the receiver antenna terminal is grounded via the CW key when using a common antenna), you can hear your own signal but it seriously overloads the receiver.  Then, you must turn the Gain control all the way to minimum to produce a usable sidetone.  A bit of an annoyance if you are used to having KenYaeIc appliances do all the fun stuff for you.  In typical military comms applications you would likely be transmitting on Freq X while receiving on Freq Y, therefore loosing the ability to monitor your own signal.  Takes some getting used to – just “feeling” your fist via the key.

Comm Center, Forward Operating Base (FOB) “PIGOUT”
Above is the basic field setup with the TX and RX powered by the “small” PP-2685 AC power supply and a gas-driven generator, the G-43 standing by.  TM 11-5820-474-14 (18MAY1962) indicates the use of the G-43 hand cranked generator. However the G-43 is functionally interchangeable with the GN-58 and I am not sure when the change from the ’58 to the ’43 occurred. Still looking for a reference on the GN-58 configuration. We were running a coax-fed 40 meter dipole up about 15 feet with a separate 64 foot wire for the receiver. Folding stool and big crystal collection optional while on operational missions.

Ditty-Bopping in the Mountains. An effective, reliable radio.

Above is the same system in action, as used to work WA6OPE on 7050 KC at 2000Z, a 120 mile shot, human powered. Good daytime signals with GRC-109 sets on BOTH ENDS of the contact.  Here we were running the set with the G-43 hand cranked generator and CN-690 Voltage Regulator module to power both the transmitter and receiver.  A pretty good workout (I’m told)!  Without a BA-48 battery just to power the receiver, the hand cranks must obviously be going for both transmit and receive – not recommended for casual operating…  So we compromised later on – ran the receiver off the PP-2685 on AC power for continuous tuning and the G-43 genny to power the TX only on this Op.  Cheating, but effective and easier on the non-Ham power source (who would rather be fishing…).

I had sent the above photo to Ray at Electric Radio Magazine for consideration in the “Electric Radio In Uniform” department.  I guess he liked it, he ran it in the Nov 2011 issue.  I guess he REALLY likes it – he ran it again (by mistake) in the April 2012 edition.  I guess some hams resonated with it – I have gotten some nice feedback on the ’109 in the woods operations.

Below is the ’109 at work in a different camp sending out the daily Fishing Report (got skunked AGAIN).  I was running it off the PU-181 generator (120VAC) at the time..  That generator is well suppressed – unlike my reliable but ignition-noise plagued Honda EX1000.  More on THAT piece of hardware later… The audio output of the GRC-109 receiver is 4000 ohms so an old pair of Hi-Z headphones with tip jacks works great.  I don’t have the issued-headphones just yet.  I often run it with a simple “amplified speaker” as seen here.  It’s from Radio Shack (horrors!) and is just a simple amp using a 486 amplifier IC driving a small speaker, the small white box seen here.  Works great when you don’t want to wear headphones.  Like public demo’s….

Also, I like the built in key but I usually use the J-45 “leg iron” key as shown here – more comfortable for long CW sessions.  It appears that I was using separate wires for TX and RX.  After many years of working HF CW, I have found that almost any piece of wire you can get up in the air will work well, producing many contacts.  Dipoles have the highest performance/complexity ratio and are my usual favorites in the bush.  A pair of dipoles on 80/40, fed by a common coax works extremely well and is simple to get up.

My camping buddies always prefer to arrive at the LZ a little late – helps them avoid big dents in their vehicles while I am slinging 8 ounce fishing weights up over the trees. A source of great amusement for them but I have found nothing better than that simple expedient. Easy work to put a dipole up to 100 feet high, but usually much lower. I’ve become a pretty good shot with these. I use the anchor line sold for duck decoys as the antenna halyards. Lightweight, strong, stealthy. Better than 550 parachute shroud line which is harder to launch and much more visible.  Wear gloves!

Again, much info on the Web regarding these radios so I will continue to focus on my experience with my set and its use in the field.

Above: The GRC-109 in camp for Vintage Field Day.

Below is another shot of the GRC-109, this time paired with my Command Set operating on another Vintage Field Day from another riverside campsite. Fun radios.

AR