AN/GRC-109 “Special Forces” Radio Set

UPDATED 5/13/13:  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,  Navy PTF boats and others, it did the job well.

Extremely rugged and even designed for possible 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 and operating LOOOONG after those custom LCD displays and proprietary microscopic microprocessors flame out in all those modern, boring appliances.

When repair by Swaptronix isn’t an option…….

The iconic drawing from the manual.  Just makes you want to be there!

Listen in !  Click the “arrow” button…

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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 and early 1960′s.  They are almost identical in appearance and operation.  The Army adopted the RS-1 (circa 1961) 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.

The US Navy also installed them on the Nasty and Trumpy Class PTF boats for unconventional warfare (U/W) operations “up north” in Vietnam. See the Fast Patrol Torpedo Boats posting elsewhere on this blog. Most “US attributable” equipment was removed from the Norwegian-built Nasty PTF’s in the early phases of MACV-SOG’s OPLAN 34A, however in later years the GRC-109 sets were retained aboard the boats as a primary communications system for long range comms back to DaNang. Declassified Operational Summary documents do not note the difference between the GRC-109 and the RS-1 sets aboard these boats; such nomenclature detail was not germaine to the report authors at the time.

On the PTF missions, the sets operated on split transmit/receive frequencies, crystal controlled CW circuits. It says a lot about the reliability and capability of these low powered CW radio sets in that critical application.  The declassified 1970 Operations Summary report noted the following freqs for CW with the GRC-109 (incorrectly identified as the RS-1 in the document): Transmit/Receive: 4069.3/8217, 4258/4632, 6220/3493 KC as primary, secondary and tertiary circuits respectively. Split T/R operation would have been routine and its likely the Ops officers/OinC’s had authority to pick the best freqs for day/night operations, the “hot work” happening mainly at night. See Reference (7), MACV-SOG Maritime Operations.

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, carrying handles 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.  Once set up and wired together (no thinking required) they are quite easy to operate.

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 !

In addition to the GRA-71 CW Burst Keyer (primarily a transmission-security device), the GRC-109 and RS-1 could have also been used directly with standard offline encryption as well. This would include the M-209, One Time pads and other approved cyphers. Since those were available and considerably smaller / lighter than the GRA-71 it is not hard to guess that they saw considerable use as well. This of course depended on the particular Op Area and transmission security considerations at that time and place. See Mark’s excellent site and his work with the M-209 and other related equipment  WWW.NF6X.NET
Mark has also done an impressive job in decoding/demodulating the GRA-71 system with modern data acquisition and software techniques.

Above: the GRA-71 Code Burst Keyer kit (upper right) is seen along with the GRC-109 system. It is powered directly by the transmitter via the front panel connector which also carries the keying signal. (The big green radio in the upper left is the BC-683, a VHF FM Tank radio receiver from WWII; not part of the GRC-109 system).  In using the GRA-71, the operator manually keys in an encrypted morse code message on a magnetic tape cartridge.  This tape is then used to drive a keyer connected to the transmitter – which then transmits the message at 300 words-per-minute (WPM).  Obviously a shorter transmission than the usual 20-25 WPM message sent with a telegraph key.  The received message is recorded on a tape recorder back at “base”, slowed down and then decrypted.  To the enemy’s ears, its just a very short noise burst that is difficult to detect, tune in, record and most importantly, locate with Radio Direction Finding (RDF) equipment.  By then, the Team is gone.

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.  Also see Peter McCollum’s excellent GRC-109 article here: http://www.militaryradio.com/spyradio/grc109.html  It includes some photo’s of the GRC-109 in operational use with the US Army Special Forces.

The GRC-109 was also utilized as the primary communications set by allied agents working behind enemy lines in unconventional warfare operations in Vietnam and elsewhere in SEA, again taking advantage of the long range and ruggedness of this system.  It was noted that Comms were dependable with this system however it was also noted that the weight of the GRC-109 set with its heavy and bulky hand-cranked generator reduced the mobility of these men.  (See Reference 1, MACV-SOG Communications).

The GRC-109 / RS-1 was also used by Special Forces world-wide, beyond SEA 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 (see below) although it’s possible it was made under a foreign sales contract to support these radios being used by our allies. – Or not -

It seems that operational experience with the GRC-109 and its relatives spawned some growth in this type of radio as technology improved.  The mission-needs remained similar.  The transistorized PRC-64 and PRC-74 and 70 came along shortly thereafter along with the TRC-77.  Another interesting set I recently became aware of is the TAR-224 made by Avco in Cincinnati Ohio.  This is clearly in the lineage of the GRC-109 with the AM voice capability of the PRC-64 added – along with 12 volt DC primary power, GRA-71 burst keyer capability, bullet proof environment protection and an optional frequency synthesizer capability.  20 watts transmitter output and only drawing 50 ma on receive.  It’s unusual nomenclature and lack of much mention of it “in the literature” makes it all the more mysterious.

But back to the ’109:

The R-1004/GRC-109 receiver can be operated by itself using the BA-48 dry cell battery as configured above. In this application the transmitter would likely be powered by the hand cranked generator directly. The battery provides 1.5 VDC and 90 VDC for the receiver circuitry only.

Apparently they were reliable and quite successful in the Special Forces and “unconventional warfare” networks in Vietnam. Their use was favored as “long range and dependable” even long after they were being “replaced” by the PRC-64 and PRC-74 radios. Due to their simplicity and all-weather ruggedness, I would assume they were also more reliable than the AN/FRC-93 (AKA: a modified Collins KWM-2A) that SF was beginning to deploy at SF camps.  (That radio was also capable of SSB voice communications which the GRC-109 transmitter could not provide.)  Especially when you consider that the FRC-93 required AC power and associated generator not to mention the serious environmental protection absolutely required by them.

The GRC-109 could use a wide variety of available AC voltages and frequencies, a 6 volt wet cell vehicular battery 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. The reference states that as a protective measure the wire antennas were sometimes 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 75-270 VAC (40-400 cps), an optional 400 cps UGP-12 gas fueled generator, 6 VDC from that captured T-54 tank battery or a G-43/GN-58 hand cranked generator, they could be used anywhere.  The UGP-12 “power unit” provided 115 VAC at 400 cps so one of the PP-2684/5 power supplies were also required when the generator was used. 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.  Arguably the most “bullet proof” radio set in the US military inventory, even (especially) by today’s standards.

Above: The designers of the RS-1/GRC-109 obviously had in mind the need to use this set anywhere in the world under almost any conditions. The versatility of the primary power source options shows someone was not only thinking, but also had input from operational users. They did their homework during the design review process. These options apply equally to the GRC-109 or the RS-1 sets. Image from the Manual.

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.

A typical “camp” station of mine, here 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.  (This IS why you go camping, isn’t it?)  You can also use it to get the latest soccer scores from Radio Australia or coordinate your operations with a time-tick from WWV, BPM or RWM, depending upon your Op Area.  Or just get a good laugh from Radio Havana Cuba, “Free Territory of the America’s” on the shortwave bands.  Reminds you of why this type of radio was designed and employed in the first place.  I wonder how many are buried in Cuba………..

The transmitter will load anything, much like the RS-6.  The GRC-109 however does utilize a Pi Network in the antenna circuit unlike the simpler RS-6 set. 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.

Above: Our setup during Electric Radio Magazines “Vintage Field Day”. Much more fun than the very fun ARRL Field Day. Here we were running the GRC-109 along with a Command Set at a favorite campsite. We could switch the Command Set between 40 and 80 meters by just plugging in a different transmitter – the setup included both receivers. PU-181 generator, dipoles, slant wires etc.  The power supply on the left powered the Command Set gear – no dynamotors in this system right now.

Above: Yep – it’s a cheesy photo – but this was Vintage Military Field Day as far as we were concerned. Makes perfect sense! That’s “Army Al” briefing our perimeter defense force.

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. Well suited for transport as a “suitcase radio” it would be a bit heavy if it included the AC power supply as shown here. Not needing the ruggedness of the GRC-109, an RS-6 set would be better “suited” for this mode of transport and concealment.

Willing to bet there are many still in eastern Europe, 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, quiet 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. This version has the gray wire (off to the right) with a 4-pin plug to power the GRC-9 receiver as well.

I am currently developing a similar 12 Volt power supply to provide the 450 VDC B+ voltage to the transmitter.  When complete, I will integrate both supplies into a single unit for use in the field when running off a 12 volt garden tractor battery.  See the “Design and Engineering Projects” Category from the list on the right for more details on these supplies.

Above: The beginnings of a packaging job for a 12 volt DC-DC power supply to power the GRC-109 transmitter and receiver in the field. The breadboard prototype is working well. This supply will also be able to power my RS-6 set but as usual, the connectors are a challenge. The case is a spare case casting for a GRC-109 transmitter. There will be enough room inside to include a GRC-9 power supply as well.

My set came from Fair Radio as have all others that I know about. Mine worked “as shipped”. It has obviously seen a lot of operational service, it’s 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 (see power supply in the “suitcase” photo, above). Wonder who that unit was….

The guys at Fair Radio told me they had obtained all their GRC-109′s from the Tobyhanna Army Depot in Pennsylvania when the Army eliminated them from inventory. “Hundreds” of sets were obtained by Fair but none came directly from overseas sources. Tobyhanna was apparently the Army’s item-manager for this system. Fair said that they sold quickly, mostly to US customers but some went overseas. This was before the US decided to “demilitarize” surplus comm gear prior to release as they are doing these days. Thankfully the GRC-109′s were spared that fate but I know of some real horror stories of equipment getting into the wrong hands back in those days. But then again the US DOD is not in the business of keeping a small group of old radio collectors happy – even though we paid for this gear…..

Above: The Maintenance Kit, Electrical Equipment MK-833/GRC-109. This kit with its watertight snap-on lid contained spare parts for the radio set. This included a complete set of spare tubes, fuses, lamps, tools, antenna insulators, adapters, vibrator etc. All contained in the Case CY-4621/GRC-109. There is plenty of extra room in the case for crystals, antenna wire, and interconnect wires. My kit is not yet complete – still working on finding some of the parts but this kit will keep me going for a long time. Like the radio sets themselves, this case could be buried in a swamp indefinitely – good sturdy gaskets and firm closures.

Back to the design: One unfortunate problem they have is the receiver is starved for antenna signal when the antenna is routed through the transmitter during “key up”, especially on the higher frequencies. 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 although they can be tedious if done frequently. The plain GRC-109 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. Carry spares….

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. But then again, you are using the GRA-71 Burst Keyer to send your operational traffic aren’t you? Then, a non-problem.

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. Sending Morse Code with an effective, reliable radio. In any Clime and Place….

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 liked 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.

Here, the G-43 generator is putting our half-power while refueling.

Above: Training future radio operators from the “Young Marines” youth program at the US Marine Corps Mountain Warfare Training Center near Bridgeport CA. (see “Young Marines program” post elsewhere on this website.)  Here the kids were learning to set up and operate the GRC-109 and learned to send their first names in CW to another group operating a GRC-9 nearby.  “Let me try!”…

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!

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

Above: The HF CW station we used at the Military Radio Collectors Group meet at Camp San Luis Obispo in April 2012. We passed CW traffic to our deployed stations and then used the PRC-25 and PRC-6 to coordinate further Ops. HF antenna was a low dipole, 3885 Kc. Lots of guys up on the HF freq with a wide assortment of WWII gear.  A BC-191 and BC-348 on standby in the background…

Note the GRC-109 receiver has a crystal plugged into the socket. I was operating on 3885 KC. If you’ve ever operated a the R-1004 receiver with crystal control, you notice that the receiver antenna noise (sensitivity) may not peak up exactly at that crystal freq. As you then rotate the tuning dial you are tuning the antenna and RF Amp circuits – they may peak at a different freq than the crystal (Ideally this would not happen but it’s tough to align any receiver to track that well). It’s likely that military users primarily used crystal control for the receivers – and so one possibility is the techs may have peaked the Ant and RF Amp circuits to the crystal freq rather than the dial/LO frequency therefore providing max sensitivity on the crystal freq. But someone aligning the receiver later would think the receiver was mis aligned… Of course this all depends upon the units involved, their Comm plans, freqs available, support available and a host of other factors. Try it – bet the receiver tuning does not “peak” at the crystal receive freq.

Below is another shot of the GRC-109 in the field, this time paired with my Command Set operating on another Vintage Field Day from another riverside campsite. Sun starting to go down? No problem, just plug in the BC-696 Command Transmitter into the rack. Fun radios.

RYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRYRY
But Wait! There’s More !!

Below: Another field Op with the GRC-109 up in the mountains. June 2012.  We were using the PRC-74 dipole assembly on 40 meters, up about 25 feet (plus 8000 feet of mountain below us). The GRC-109 was being powered by the PU-181 as usual.

Above, FOB Shangri La, running CW contacts on 40 meters, here working WA6RND down in Orange CA. 350 miles.  The dark wire in the foreground is the feed line for the dipole. The yellow wire runs off to the generator. The separate receiver antenna wire runs up into the tree.

This weeks’ mission: Establish surveillance of the Sonora Pass (distance) from an OP at Forward Operating Base Shangri La. Detect, track and report suspicious wildlife, BigFoot or alien activity. Primary Guard frequency: 7050 Kc.

Above – Alex setting up a PRC-74 dipole antenna for the GRC-109 on 40 meters. Although not designed for the GRC-109, a dipole is a dipole and this PRC-74 antenna makes a useful addition to the kit.  A big advantage to using a balanced antenna like a dipole is there is no need to ground the transmitter, either with a stake or ground radial array. Perfect for “shoot and scoot” Ops. Not so with a long wire, vertical, inverted “L” or most “antennas of opportunity”.

Or, if you want to be “true to the manual”, sling up the 100 foot “hank” wire antenna as an inverted “L” and then pound in a ground stake.  It will work pretty well.

Above: The PU-181/PGC-1 generator powered the GRC-109. This is a 2-stroke, 300 watt generator strapped for 120 VAC. It can also be set up for 240 VAC if needed. Weight: 56 pounds. It will run a long weekend of field ops on a tank of gas mix. Well suppressed, it starts on the first pull, every time. Even at this 8100 foot elevation. A little noisy, a little smokey, a little heavy, a lotta reliability. It still has the original Korean War vintage spark plug installed. You don’t get rugged reliability like this with modern consumer-grade junk.

Above – Alex is tuning the transmitter. Note the separate receiver wire antenna heading up into the trees.

The GRC-109 set up on a handy Cedar table high in the mountains, ready to go.  The field antenna kit was essential as usual – carries enough parts for the 75 meter dipole at base camp plus the 40 meter dipole and receive wire and the 60 meter slant wire antenna at this site.  Trees were pretty far apart here so those long heaving lines were necessary.  Eight ounce sinkers are  the optimum weight for launching (light enough) but heavy enough to pull the line down through the branches.  Alex noted that that Red jumper wire intended to ground the receiver to the transmitter chassis was plugged into the Rx Ant jack on the transmitter by mistake.  Didn’t matter – we were using a separate Receiver antenna.  The GRC-109 is pretty soldier proof.  That mistake just grounded the receiver chassis upon key down.  It is “grounded” by the power supply connectors anyway.  Thin air at 8100 feet can cause these things!

Above: I love the sound of CW in the mountains! We are even that much closer to the ionosphere.

Above: The GRC-109 operated while inside my transit case. We were operating the receiver for extended periods on battery power with my “BA-48 Simulator” switcher supply and the PU-181 to power the transmitter as necessary.

Above: Another nice spot for a “Camp with Comms”. FOB Wendy.  Very quiet location

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The 18th annual muster of the West Coast Military Radio Collectors Group was held May 2-4, 2013 at Camp San Luis Obispo (CA). I had the GRC-109 set up along with a PRC-25 for Net Control of a VHF field exercise that included this PRC-6 up on a nearby hill.

Above: The setup I used to copy the encrypted CW transmission from Coast Station KSM in Bolinas CA. I copied the M-209 encrypted message using the GRC-109 with just a simple 40′ wire antenna thrown up on the roof of the building.  It worked great over this 200 mile “NVIS” path. Once again, the ’109 being operated from inside a re-purposed transit case to permit rapid relocating after transmission! After the receiving exercise (26 Group message) I then called K6KPH (co-located with KSM) to acknowledge receipt of the message and then received from them a congratulatory Radiogram marking the successful conclusion of the exercise. See the MRCG-MRHS Exercise Post elsewhere in this blog.

The message sent by KSM was an actual message received by Merril’s Marauders during combat operations in Burma during WWII.  The KSM message was encrypted with a “current” keylist for the M-209.  The Groups read:

AAMKD BPCFM LFRCS GCAYX HNOIT

JSJRN BSGWD KHZHZ UMXJD EICBU

HZUTA SJJKX WSPEQ MELZD GQRXU

GKJWM UYLMJ AQKPA YAABL SZRDK

TUBBQ AAUNO RDORI WJXXX AAMKD

BPCFM

Upon decrypting using the M-209 the plaintext message read:

YOUR MISSION COMPLETE NEW MISSION COVER SOUTH APPROACH TO TANAN BE PARTICULARLY CAREFUL OF YOUR RIGHT FLANK

Good exercise – CW proves its worth once again.  A longer RATT message also sent did not fare so well – the GRC-46 RATT set could not handle the severe local RF noise and signal fading as well as the GRC-109 on CW.

AR