AN/GRC-109 “Special Forces” Radio Set

UPDATED 10/18/16:  Probably my favorite “Black Radio” despite its few quirks. The “COOL METER” is Pegged on this one… They were used extensively from the early 1950’s (as the RS-1) through the 1970’s and beyond by the CIA, Special Forces, other US military and allied units worldwide. That included US Navy PTF boats and Army LRRP units; it did the job well.  In direct lineage from the SSTR-1 set used by the OSS in WWII; it includes a “mystique factor” second to none..

Extremely rugged and designed to survive parachute drops, they were built to withstand lengthy burial in the ground or even under 16 feet of water as part of a clandestine equipment cache. These sets have a Cool Factor 36.6 db higher than any plastic RiceBox ever made by KenYaeIc. They were, and are extremely reliable, rugged and quite EMP-resistant. The “GRC-109″ will be operational and operating LOOOONG after those custom LCD displays and proprietary microscopic microprocessors flame out in all those modern, boring “computers with antennas”.

The AN/GRC-109 is eminently usable in stock configuration, without any “Hammering” modifications by Hams or others. A Radio Operator’s radio.
They will find them very simple to plug together, tune up and make contact. However, today’s “appliance operators” will surely turn up their noses at this set.

The Tech Manual is TM 11-5820-474-14 and is available on the Interwebs.

The GRC-109 described below is my “Daily Driver”.

When repair by Swaptronix isn’t an option……………………Ditty Dum Dum Ditty

From the GRC-109 manual

So there I was……..
The iconic drawing from the manual.  Just makes you want to be there.

Listen in !  Click the “arrow” button…

Audio clip: Adobe Flash Player (version 9 or above) is required to play this audio clip. Download the latest version here. You also need to have JavaScript enabled in your browser.

(Cut Numbers crypto transmission from the Socialist Utopia of Cuba, 5800 Kc, late one night)

The “Angry 109″: The AN/GRC-109 is the Army’s designated follow-on to the CIA’s RS-1 radio set which had been in widespread use by them and the US military in the 1950’s and 1960’s.  They are essentially the same in operation and appearance, except for the panel labels and transmitter antenna and keying connector layouts.  Much of the following applies equally to either set, as noted.

The Army adopted the design of the RS-1 (circa 1961) as the AN/GRC-109 to be supportable with standardized training, repair parts and depot maintenance within the Army supply and logistics system. (More on that below.) Subsequent Modification Work Orders caused the GRC-109 to further diverge from the RS-1 design with minor modification and usage upgrades.

Anecdotal evidence has GRC-109’s in Special Forces unit inventory as late as 1978. They were being overhauled at the Tobyhanna Army Depot as recently as 1983.

The Department of the Army Radio and Radar Reference Data manual, FM24-24, dated December 1983 still listed the AN/GRC-109 as “Standard A” issue. “Current inventory item available to fill operational requirements”. NSN 5820-00-892-0881 (Reference 36).

Special Forces team radio gear.  Photo courtesy of W1OC

Special Forces team radio gear. Photo courtesy of W1OC

Above: A mid 1970’s photo of the US Army 10th Special Forces Group (E) team radio equipment laid out for inspection. In addition to the two complete GRC-109 sets, note the GRA-71 Code Burst keyers, the PRC-74 transceivers, PRC-25/77’s, PRC-90’s and the Homelite XLA115/1/400/1P gas powered, 400 cps AC Gensets for the GRC-109’s. Accessory gear included the G-43 hand cranked generators, AC/DC power supplies, antenna bobbins, spare parts kits, camera kit, 7×35 and 10×50 binoculars. By the time of this photo, the PRC-74 was taking over the comm tasking formerly met with the GRC-109’s but the 109’s were still in active inventory.

It is clear that early in the Vietnam war the GRC-109 was a primary long-range communications workhorse of MACV-SOG operations (Military Assistance Command Vietnam – Studies and Observations Group). Prior to the stand-up of MACV-SOG in 1964, the CIA would have used the earlier RS-1 sets in previous comm circuits in Southeast Asia in the late 50’s and early 60’s.

It can also be surmised that MACV-SOG units inherited some RS-1 sets from their predecessors and continued to use them post-1964 in Southeast Asia, when or where they were available. The historical record does not always differentiate between the sets in field use. From a “report writers” perspective, they may have been considered to be equivalent. The CIA’s RS-1 set was very likely in use by the US Army and others in that earlier time frame before the GRA-71 high speed burst keyer appeared, the necessary transmitter design modifications introduced and communications doctrine changed to require the usage of “burst”.

G-43 Generator with GRC-109

G-43 Generator with GRC-109

Above: The GRC-109 powered by the G-43 hand cranked generator via the CN-690 Voltage Regulator. Earlier sets were powered by the older GN-58 Generator; they are functionally equivalent. Some fun with the camera: DZ Back Yard

Reference (3) describes some of the use of the GRC-109 by US Army Special Forces in Vietnam. It states that the GRC-109 was not issued to conventional US Army or South Vietnamese units in that theater, ostensibly because it transmitted CW-only. Other references imply wider spread Army usage. In those days, regular Line infantry units in Vietnam primarily depended upon the easy-to-operate tactical voice radio systems they had available, especially as the CW skills of many RTO’s atrophied along the way. This was especially true considering the limited geographical TAOR that most regular Army units operated within; and that was usually (ideally) within range of their supporting artillery (and VHF radio range).

Long range recon units in Vietnam probably had the GRC-109 in addition to the Special Forces units. However, LOS VHF voice-to-relay sites or aircraft within South Vietnam would have dominated, since it was easier, faster and we had air supremacy above that country. In contrast, the Long Range Reconnaissance Patrol (LRRP) units in Europe routinely used the GRC-109 for their primary communications of Intel back to G2 at their base (Reference 38). However, they were training for operations “further east” in western Europe where air supremacy would not be assured; hence, HF.

The GRC-109’s were deployed at SF camps and in fortified villages throughout South Vietnam as the only means of reliable comms back to HQ and, initially, between themselves for mutual support. This was true especially in the “early days” and later on they were used as backup systems to the AN/FRC-93’s (Collins KWM-2) as those became available in fixed camps. The KWM-2’s were far more fragile and arguably far less “soldier proof” than the GRC-109’s however. Also see Peter McCollum’s excellent GRC-109 article here: It includes some photo’s of the GRC-109 in operational use with the US Army Special Forces in Europe and Southeast Asia.

The GRC-109 was also utilized as the primary communications set by indigenous personnel working behind enemy lines in unconventional warfare operations deep inside North Vietnam (Reference 1, MACV-SOG Communications). Notably for their long range but also because on-scene air support (and its inherent radio voice / relay possibilities) was not in operation.

The predecessor RS-1 was also likely used by US led teams operating in Laotian and Cambodian border areas (later to become SHINING BRASS recon patrols), initially as they took over those missions from CIA control prior to 1964. The GRC-109 was also used early and elsewhere in Southeast Asia, 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, especially with its heavy and bulky hand-cranked generator reduced the mobility of these men working on MACV-SOG missions. (Reference 1) Of course, the PRC-25/77 VHF and URC-10 UHF radios were commonly used for coordinating extracts with the Forward Air Controller and supporting strike aircraft where voice was the only practical mode after the PRC-25’s became deployed in 1965 (Reference 44 et. al.)

From Reference (1):
3) To support SHINING BRASS teams, AN/PRC-25 (FM) ground-air radios were procured as well as AN/PRC-64’s (CW/AM) for field-base use. The PRC-64 was issued to replace the bulkier and heavier AN/GRC-109 radio.
SHINING BRASS communications between the C&C detachment, the FOBs and launch sites consisted of CW and voice radio utilizing one time pads or operations codes. Communications from the teams to launch sites consisted of CW initially but also via voice as that evolved. As PRC-25s were introduced, an FM voice capability between the team and base evolved by utilizing forward air control (FAC) aircraft as relay points. High points in Ground relay stations established at sensitive areas inaccessible to the enemy due to terrain features were also activated to assist teams in communicating with their base.
4) Despite its heavy weight, agent teams in NVN continued to use the GRC-109 in 1965 as it was the only dependable equipment available to meet their long-term requirements.”
[my emphasis added]

The US Navy also installed GRC-109’s on the Trumpy Class (and probably also the Nasty Class) PTF boats for unconventional warfare (U/W) operations “up north” in Vietnam. That inclusion makes sense since many of the PTF missions to North Vietnam were to insert and extract cross-beach commando teams that were primarily equipped with the GRC-109’s. The PTF’s installed ARC-94 SSB/AM/CW sets could not operate CW on split frequencies with the teams’ GRC-109′, so that type of comm channel is very understandable. See the Fast Patrol Torpedo Boats posting Fast Patrol Torpedo Boats (PTF-17) 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 or elsewhere. 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 significant to the report authors at the time.

Below: A post-war (1975) photo of PTF-17 that was equipped with a GRC-109 set among other radio systems.



On the MACV-SOG PTF missions, the boats operated on split transmit/receive frequencies on these crystal-controlled CW circuits. It says a lot about the reliability and capability of these low powered morse code radio sets in that critical application.  The declassified 1970 MACV-SOG Maritime Operations Summary report (Reference 7) noted the following freqs for CW with the GRC-109 (incorrectly identified as the RS-1 in the document):

4069.3 / 8217 KC  Primary
4258 / 4632   KC  Secondary
6220 / 3493   KC  Tertiary

Split T/R operation would have been routine and it’s 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.
It is interesting (distressing) to note that Reference (1) describes a 6-11 month delay in obtaining new crystals via the SOG Logistics Support Department in Okinawa. This is especially strange since the FT-243 crystals used by the GRC-109 were readily available from numerous US commercial companies for use by Ham Radio Operators for a few dollars each. These either from the massive WW2 surplus crystal stocks readily available, or custom made for specific frequencies on short notice.

The T-784 and RT-3 transmitters include provisions for 2 different types of crystals via independent sockets on the front panel.. The “upper” set accommodated FT-243’s but the “lower” set is designed for 1/8 inch pins with 3/4 inch spacing. I’m not sure what holder the lower set may have been for. But again, built-in versatility.

It is not known what the in-country inventory of spare crystals was available over this time period. Maintaining tactical comm circuits on the same frequencies for long periods of time is very dangerous but this delay implies that this may have been the case. In contrast, today’s tactical SINGCARS radios automatically change frequencies over 100 times every second.

Note the Tertiary transmit frequency of 6220 KC. It is interesting to note that frequencies between 5.0 and 6.5 MC were not possible with the AN/FRC-93 (Collins KWM-2A) radio transceivers used widely by land-based MACV-SOG units. (This was due to internal conflicts with the transceivers’ intermediate frequency amplifier systems.) So who would the tertiary circuit been with – who had something other than an FRC-93? NAD Da Nang (at Command and Control North) had URC-32’s – no problem, nor with any Navy ships. Someone, somewhere, sometime figured out this incompatibility. Just an interesting footnote. Or it could also be just a typo in the reference – there are many.

With a transmitter output of between 10 – 15 watts, a built in key that works well, versatile power supply options and a sensitive receiver, they did the job.  The transmitter covered the frequency range of 3 to 22 MC in 4 bands; the receiver covered 3 to 24 MC in 4 bands.

Note that the frequency coverage is not the usual 2-12, or 3-8 mc of many tactical HF radios of the era. Those were intended to provide local or NVIS coverage over circuits beyond VHF FM sets, out to a few tens of kilometers or sometimes a bit more. The inclusion of the higher frequency bands in the RS-1/GRC-109 out to 22/24 mc is testament to the operational requirement for comms over thousands of kilometers in addition to more regional ops. That is telling.

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.

A Modification Mystery: Some “Internet Folklore” states that most or all of the original “unlettered” 109’s were subsequently modified to add the code burst connector. The modification document sometimes implied was MWO 11-5820-474-35/1.
As stated in TM11-5835-224-12(1) that MWO was to “modify the T-784 transmitter for use with the GRA-71″. (I have never found the actual MWO wording. Did the “T-874 Transmitter” noted already have the code burst key connector?) But what did this MWO actually accomplish? Just minor circuit improvements?

I don’t think that the original T-874 transmitters were modified by simply “adding” the code burst connector to the front panel. This would also require the relocation of the Receiver, Key and Ground posts (and corresponding panel holes) to accommodate the multi-pin GRA-71 connector. The original AN/GRC-109 was allegedly just a renaming of an RS-1 set. However the panel layout of the RS-1/RT-3 transmitter is different from the GRC-109 “plain” T-784 transmitter, so something else was going on here. Was the “unlettered” T-784/GRC-109 transmitter built as an entirely new transmitter from the ground up with the Code Burst connector and its unique front panel and labeling.? (That is my working theory.)
Or did the modification require an entirely new front panel (with all the internal transmitter parts then having to be removed and reinstalled on this new panel?) Unlikely in my opinion. (The later T-784A/GRC-109A appears to have the same transmitter front panel hole layout, with the addition of the burst keyer connector as the basic design.)

Has anyone ever seen a T-784/GRC-109 without the GRA-71 burst keyer connector? I have not. More research needed here.

The RT/D-3 variant transmitter does appear to be a modified RT-3, with the external key terminal post removed and the GRA-71 keyer connector appearing in its place. See photo further down the post of an RT/D-3 which also sports the white MWO-39 stamp on the front panel. Was the RT-/D-3 the first step towards the T-874/GRC-109 transmitter? It may be.

Once set up and wired together (no thinking required) they are quite easy to tune and operate. They are eminently usable “as-is”, no “mods” or “conversions” required or desired. In the hands of an experienced operator, they would get you where you needed to go comms-wise.

Below is the CIA’s RT-3, the transmitter of the RS-1 system. That post-WWII system was developed in the late 1940’s with a principal requirement for ruggedness aside from the usual RF performance.  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 external CW key and receive antenna connector posts.  No other “US” markings – I bet that fooled ’em !

RT-3 Transmitter from RS-1 System

In addition to the GRA-71 CW Burst Keyer (primarily a transmission-security device; it is not a cypher machine), the GRC-109 and RS-1 could have also been used directly with standard offline encryption as well. This would include DRYAD pads, the M-209, One Time pads and other approved cyphers. Since those were available, 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  NF6X.NET
Mark has also done an impressive job in decoding/demodulating the GRA-71 system with modern data acquisition and software techniques.

GRA-71 Code Burst Keyer with GRC-109

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 GRC-109 transmitter – which then transmits the message at 300 words-per-minute (WPM).  Obviously a shorter transmission than the usual 15-20 WPM message sent with the built-in, or external telegraph key.  Back at the Base, the received message is processed (by the GSH-17 system) and recorded on a magnetic tape, slowed down and then decrypted.  To the enemy’s ears, it’s just a very short noise burst that is difficult to detect, tune in, record and most importantly, to locate with Radio Direction Finding (RDF) equipment.  By then, the Team is gone.

I believe the GRA-71 may have been designed and built specifically for use together with the GRC-109, I can find no usage of the GRA-71 with earlier transmitters. The burst keyer of course was used with later sets such as the PRC-64A, PRC-74 (A, B and C models), TAR-224 and probably others. More research needed here.

The GRC-109A system (less incorrect speaker) set up for AC powered Ops

Above: The GRC-109A Model: T-784A transmitter, R-1004A receiver and “small” PP-2685A AC power supply set up ready to go. That speaker was inappropriate, but handy for initial checkout (where did I put those headphones?)  With the receivers’ 4000 ohm output impedance, it will drive a 600 ohm speaker in a pinch. Improvise, adapt, overcome.  Note the separate transmitter and receiver wire antennas.  This particular set was an old service veteran but it had been packed away for over 25 years since even those days.  It fired right up. My right thumb can attest to that!

The GRC-109 / RS-1 was also used by Special Forces world-wide, beyond Southeast Asia in the 1950’s – 60’s and likely beyond. But how far beyond? I have seen a BA-48 battery (also used with the GRC-9) with a date code of May, 1984 (see below). Fair Radio Sales is currently selling (“weak”) BA-48 batteries with 1986 date codes. (I am not aware of any other US radio sets besides the SSTR-5 and SCR-694 that used the BA-48.) It’s possible they were 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 hybrid TRC-77.  Another interesting set 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.  Covering 2 to 24 MC, it is fully transistorized, with a built in motor-driven antenna coupling network. It’s unusual nomenclature and lack of much mention of it “in the literature” makes it all the more mysterious. Anecdotal references have it being used by the CIA well into the 1980’s.

I have learned that the Jet Propulsion Lab in Pasadena worked on a project to convert the AN/GRC-109 from its vacuum tube technology to an entirely solid state design. This information was provided to representatives of the Republic of Korea as part of a Technology Transfer program in 1970 (Reference 43). Presumably the ROK’s were using the GRC-109 then as well. I wonder what ever happened to that project. It may be possible that JPL’s design work eventually resulted in the TAR-224. More research needed…
Back to the ‘109:

R-1004/GRC109 Receiver and Battery

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. The issued headphones are the H-65/U but any high impedance headset will work with the 4000 ohm output impedance of the receiver. Above: receiving with a set of High Z Brandes headphones; the HS-30 headset with the C-410 impedance matching transformer is also appropriate. It will also drive any 600 ohm headset or speaker in a pinch.

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 notionally “replaced” by the PRC-64 and PRC-74 radios. (The initial deployment of the PRC-74 began with 15 sets delivered to MACV-SOG in 1967 as an interim radio to the PRC-70 which came even later.)

In 1965, fifteen PRC-64 sets were evaluated by the 5th Special Forces group in the Mekong delta and central highlands of Vietnam and its performance was contrasted with the GRC-109. The report (Reference 40) stated they felt the PRC-64 was “far superior” to the GRC-109 for patrol (my emphasis) operations but it also notes that this was due to its smaller size, weight and easier set up. Critically important differences for a small, fast moving team operating in enemy held territory. Capability wise, they were found to be equivalent by the Special Forces teams however they noted that the PRC-64’s 1.5 watt AM voice capability was unreliable. Just a few years later a MACV-SOG Communications Officers report in 1969 stated that the PRC-64 “is receiving little use but should be retained in inventory” (Reference 1). However, the future was becoming clearer – the days of the portable vacuum tube combat radio were coming to an end.

Due to their simplicity and all-weather ruggedness, I would assume the GRC-109’s were also more reliable than the AN/FRC-93 (AKA: a modified Collins KWM-2A) that SF was beginning to deploy for fixed-site work 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 substantial 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.

Powered by 75-270 VAC (40-400 cps), an optional 400 cps UGP-12 or Homelite 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 Homelite (TM5-6115-405-15) or 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.

It was “The Jeep of the radio world” as dubbed by a former Special Forces radio operator in Vietnam (Reference 53).

GRC-109 Power Options

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.

GRC-109 with UGP-12 Generator and GRA-71 Burst Keyer

GRC-109 with UGP-12 Generator and GRA-71 Burst Keyer

Above: The UGP-12 gasoline powered AC power generator in a friends’ GRC-109 system. Rarely seen in the wild, this well traveled UGP-12 had been painted white some time in the past, along with its fiberglass carrying case, for reasons unknown (deployed at Ice Station Zebra perhaps?). This 2-stroke generator was rated at 115 VAC, 400 cps, 125 watts and was designed specifically for the GRC-109. 400 cps was chosen for the generator to reduce the size and weight of the associated magnetics. Deployment date unknown but it may have been an accessory from the beginning as this set (and generator) replaced the WWII OSS SSTR-1 set with its similar gas generator. The generator is acoustically, surprisingly quiet, starts easily and smokes very little. It incorporates a shielded ignition system to suppress radio interference. (The 2 small black boxes on the left side of the photo are unrelated to the GRC-109.) That little gasoline can is cute.

UGP-12 Data Plate

UGP-12 Data Plate

Above: The data plate as mounted on the generator. Standard stuff for a 2-stroke field generator. Note the absence of origin identity, manufacturer, contract data etc. Nothing to see here, move along.

When operating without the gas generator and when plugged into an electric lamp socket in that hotel “safe house” via a screw-in adapter, their low power CW would not even blink the house lights during those 0242 hours SITREP transmissions back to base.  The set 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.

On The Air with the AN/GRC-109 “in civilian clothes”

My GRC-109 probably retired from military service in the early 1980’s but it is still going strong on the Ham Radio bands with call sign N6CC. I bought mine from Fair Radio Sales in 1984. They first appeared in their Fall 1984 catalog suppliment, probably shortly after they were declared excess by the US Army. I ordered the set for $ 109.50 which included the transmitter, receiver and the large and small power supplies. I never get tired of playing with it and testing its capabilities from remote locations, operating it as intended.

My T-784/GRC-109 serial 775 transmitter has a JAN CLRV 2E26 made by GE in Canada in 1965, the JAN-CG-6AC7WA was made by GE in 1964. This set was made by Admiral Corporation, apparently all “plain” GRC-109’s were as well. The contract for the GRC-109A models went to Oklahoma Aerotronics as I understand it. My R-1004/GRC-109 receiver Serial number 74 has tubes with date codes of 1965 and 1966, no markings or date codes on the IF transformer cans. I have no reason to suspect that these are not the original tubes.

GRC-109 Operations in the Mountains – N6CC

A typical “camp” station of mine, here on the granite, up in the Sierra Nevada Mountains, tracking and reporting submarine movements and 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 on the shortwave bands; “Free Territory of the America’s” as they call themselves. Reminds you of why this type of radio was designed and employed in the first place.  I wonder how many sets are buried in Cuba………..

My AN/GRC-109 field kit below:

As far as maximum range goes on Ham Radio frequencies, the GRC-109’s 10-15 watt transmitter is easily capable of inter-continental distances in the hands of an experienced operator and under good conditions. Especially so on the 14 and 21 MC Ham bands. Even with a simple dipole up a half-wavelength or a wire Vee Beam and aimed at your target station. It helps if you have a good CW operator at the other end and there are still plenty of them in the Ham radio ranks these days.

Just for fun, I had started on a very casual “Worked All States” effort. In a 4 week period starting in December 2014 I had worked 30 states from Hawaii to Massachusetts, Alaska to Florida, mostly all on 7 Mc, with a dipole antenna.  I’ll get them all as I have time, but the east coast states may require moving to 14 Mc. This transmitter is only about 1.7 “S” Units below a 100 watt transmitter at the receiving end but the main challenge is working with just a few crystals. I have to set up an “ambush” on my crystal frequency and wait for someone to show up there. It works, but slowly.. Calling CQ also works, but is of course, random.

I have worked Japan and South America from California with my set on 14 MC in the past. My best distance so far is 5674 miles to F6KNB in France (on 7031 Mc). You can work pretty much anyone you can hear if the other guy is skilled. On the higher frequencies the receiver selectivity/tuning rate is really the limiting factor in hearing the other guy, but above 10 MC or so the sensitivity starts to fall off somewhat as well. You need uncrowded conditions on these long range frequencies – generally not a factor in well-planned military comm circuits. On the 80, 40 and 30 meter ham bands, reliable CW comms are routine.

If you are working over an unfamiliar path or with different TX and RX equipment or antennas, you can use the online VOACAP program to help you get in the ballpark in finding the optimum frequency/time for that path.  Select TX and RX sites, TX power, transmission mode, R and T antenna types. The program then obtains the current ionospheric sounding data for the path chosen and then it runs the calculation.  This displayed data set clearly shows you what is “doable”, or not. Mission planning – It’s pretty good.  Provides a graph of circuit probability versus frequency versus UTC time of day. I use it and find that it provides reasonably accurate predictions.

The transmitter will “load” (efficiently pump power into) almost any antenna, 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.

Meanwhile: Back in the rear, with the gear and the beer…..

GRC-109 – Vintage Field Day

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.

Vintage Military Field Day

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.

GRC-109A while “Cabin Camping”

Above: The GRC-109A station set up to take food orders while cabin camping at a remote Safe House. Smoked salmon beats MRE’s any time – even when heated with used one-time-pad sheets… Here, chatting with Don, W6JL on 40 meters CW in late afternoon – a 450 mile shot.  My transmit antenna was a 33 foot wire thrown up in a tree; about 15 feet high, oriented mostly horizontally. The separate receiver antenna was similar.

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….So far, 8 of them have gotten theirs….

GRC-109 in the High Sierras

Fun Fact: One day up in the mountains with the GRC-109. That “hot pink” object in the background is an Army Signal Corps VS-17 visual signal panel laying on the rocks by the lake.  They are used to mark friendly positions when working with Tactical Air or other friendlies in the area.  We deployed it so that our camper buddies arriving late to the general area could locate our well-camouflaged position exactly from their avenue of approach.  You can see these things in the bush from many miles away although this photo doesn’t remotely capture its brightness. It must be stressing the color filters in my cheap digital camera!  In the sun, its a REAL attention getter.

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.

F-5E Aggressors

F-5E Aggressors

Above: F-5E “aggressors” in Soviet-style camo and markings (sans red stars); these 3 operated by the USAF. Official USAF Photo. No, they don’t carry GRC-109’s……

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.
But I digress……

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 at 9 and 10 pounds respectively).  Although substantially smaller, lighter and easier to pack than its predecessor GRC-9 at 32 pounds, 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. (The GN-58/G-43, cables and accessories are common to both units for weight comparison purposes).

One online, second hand anecdote I have read stated that “Special Forces personnel that I knew said they routinely threw away the GRC-109’s in favor of the GRC-9” [sic].  Might have happened to someone, somewhere, sometime but in general I don’t believe it; it doesn’t make sense. I’ve not found any actual references to that kind of sentiment.  By the 1960-70’s, the GRC-9 was already long in the tooth and the GRC-109 was specifically available for those types of operations, at least by US forces.  You would most likely be crystal controlled anyway and wouldn’t need, or want to deal with, the complications of the VFO.  You would rarely or never need or use AM voice; so why drag around the added weight, complexity and bulk of a GRC-9 in the jungle or forests or urban terrain of central Europe? A separate GRC-109 transmitter (with CN-690 VR box) and receiver can be easily split up and packed by 2 men versus a heavy, bulky GRC-9 that can’t be subdivided.  The GRC-9 is also not compatible with the GRA-71 burst-CW system either; that would be a critical shortcoming.

GRC-109 with CN-690 Voltage Regulator

GRC-109 with CN-690 Voltage Regulator

Above: The individual radio components are small and relatively light compared with the GRC-9 Receiver-Transmitter unit. Of course, the heavy GN-58 or G-43 hand cranked generator is a beast – but common to both sets while “mudborne”.

For casual Ham operation, and if I had no other choice, and if it was only at fixed sites, and if I didn’t have a good collection of crystals, and if I was not qualified in CW, if my “key” buddies were not CW qualified, if I didn’t have to carry it, if I needed to be vehicle-mobile with it, I’d pick the more versatile (for Ham usage) GRC-9 however.  That’s a lot of “ifs”.  For agent or mudborne, deep reconn operations during that era the GRC-109 would get my vote over a GRC-9, hands down. If I HAD to RELY on comms from The Bush, it’s the GRC-109 every time.  Probably even today.

That said, it would still 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.  The GRC-109’s were ultimately intended to be 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 building rooms in eastern Europe for use by stay-behind personnel in case the neighborhood went downhill again.  Any of you 05Bravo or 18Echo Vet’s care to comment?

GRC-109 Suitcase Clandestine – N6CC

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 lost THAT battle but eventually won the war. 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.

A recent E Bay sale revealed that a complete RS-6 set was found in the attic of a building in the town of Tarrenz in the Tirol region of western Austria. That cache included a complete set of encryption/decryption materials (in German) and related items in addition to the RS-6 set, large NiCad batteries and spare parts. It was placed there in 1961 in a CIA effort to train, equip and support Austrian “Stay Behind” citizens in resisting a presumed Soviet invasion of Western Europe.

There were six known RS-6/RS-1 communications caches in Austria at that time. (CIA FOIA declassified reports, Project GRCROOND, Reference 48). Those same CIA documents clearly show that these equipment caches also included the RS-1 sets along with the RS-6 radios and a GN-58 hand cranked generator as well. It is clear from this declassified effort that the radio operators involved were trained in the use of both types of sets. Good backup redundancy planning? More to follow on that. For more information on the RS-6 CIA set and the Austrian cache contents, take a look here: RS-6 Transmitter Receiver Set

The Norwegian government also ran an active Stay Behind organization in that country, beginning in 1948. That was jointly funded by the Norwegian, British and US governments well into the 1960’s but later on, solely by Norway. Many equipment caches were placed around the country for use by approximately 100 citizens groups in reporting on enemy occupation forces plus supporting partisan networks.

Wartime intelligence teams operating in Norway reported back to the exiled Norwegian government in London. These agents were particularly effective in reporting on enemy forces occupying that country and were critical in the operations that eventually sank the Tirpitz battleship in a fjord near Tromso and the attack on the heavy water plant critical to the Nazi nuclear weapon efforts..

The Norwegians learned of the necessity of partisan teams operating in their own country the hard way… Communications were critical. Radios provided by the SOE and OSS were likely involved as well as indigenous equipment.

BTW, Soviet disinformation propaganda had a field day with sinister stories about the “real purpose” of these European stay-behind organizations once their presence became known to the general public. Of course accepted by the “Useful Fools” in the west who sucked it all in.

In the 1950’s and 1960’s the principal radio set utilized for these operation was the RS-1 seen below. Earlier caches may have included WWII allied and captured German equipment as available at the time. Later comm gear also included Norwegian-built equipment. (Reference 57).

RS-1 from Norwegian Stay Behind Equipment cache

RS-1 from Norwegian Stay Behind Equipment cache

Above: An RS-1 set from one of the Norwegian caches. Note the CN-690 voltage regulator (lower right) for hand-cranked generator operation and the unusual red connectors at the power supply.

RS-1 Radio cache packaging material

RS-1 Radio cache packaging material

Above: Some of the packing materials from the RS-1 equipment cache now in the museum. The “liner” of the large wooden crate is made of lacquered sheet zinc, solder-sealed to protect the contents. Below is an older arms cache in Norway.

Norwegian Stay Behind arms cache

Norwegian Stay Behind arms cache

The above arms cache is probably from the late 1940’s and was buried underneath that rock pile in a remote mountain location in Norway. It contained a quantity of 9mm pistol ammunition and at least one 2.36″ M6A3 Bazooka round among other “energetic materials”. The supplies in this cache had long since degraded and it was subsequently “rendered safe” in-place by the Norwegian army. It is likely that communications equipment was also cached in locations like this one. The very robust environmental protection of the RS-1 set would be ideal in a cache like this. Photos from the Norwegian Troms Forsvarsmuseum Military History Museum, Tromso Norway.

The RS-1 set was also used by anti-Communist Russian expatriates operating inside the USSR in the early 1950’s. They received training in Germany (and probably elsewhere) and were then parachuted into Operational Areas as teams equipped with this set. The team package included a GN-58 generator modified for use while clamped to a tree or post. Their year-long training and preparation is described in the CIA FOIA declassified report EGMA-00713. (Reference 50)

In the US, Project WASHTUB also planned for “stay behind” personnel in Alaska to provide intel on the presumed Soviet attack and occupation of Alaska during the early “cold war”. These would be locals with intimate knowledge of the terrain, conditions, people and survival skills needed to live in rural Alaska. Potential agents were approached, selected, trained and paid to perform as stay-behind citizens – and locals with an Amateur Radio license was a prime consideration. The CW skills of Hams were a given in those days.
The source document describes notional communications with a submarine or a fixed station in a secure area. The document also mentions the use of one-time-pads. (Reference 35).
Would the RS-1 (later to become the AN/GRC-109) been an ideal radio set for this type of operating in 1950’s equipment caches in Alaska? I think so.

GRC-109A Transmitter ready for packing

Above: A friends’ veteran GRC-109A transmitter ready for cover installation. Both the basic ‘109 and ‘109A sets have space under their respective covers for some small accessories. In this instance, 5 crystals and a 33 foot quarter wave antenna wire for 7 Mc operations. The receiver carries its own antenna wire under the snapped-on cover. There was also room for a small pencil, one time pads and freq/time comm plan if you haven’t already memorized it.

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.
Speaking of the 6 Volt-capable PP-2684 power supply. When running mine on a 6V car battery the vibrator RF “hash” basically wipes out the receiver – it is unworkable. Any of you military, CIA or Ham operators of the GRC-109 been able to use the 6 volt power option successfully? If my power supply is representative, I would guess it was not very usable. Comments?

Above: Fixed-Mobile operation from camp, here running with a dipole in the trees as usual.

GRC-109 DC-DC Converter powering receiver – N6CC

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.

BA-48 Battery Simulator - N6CC

BA-48 Battery Simulator – N6CC

Above: The insides of the prototype “BA-48 Simulator” as packaged for powering the GRC-9 and GRC-109 receivers. Compact, well shielded when the cover is in place. Provides 105 VDC and regulated 1.4 VDC from a 12 volt input.  Built from available, “non-optimum” parts, it needs a PC board layout next…

I am currently developing a similar 12 Volt power supply to provide the 450 VDC B+ and 6.3 VDC to the transmitter.  This will be an updated, functional version of the elusive “PA-109″ DC-DC power supply built for the GRC-109 by Nems Clarke late in the life of their employment. This very elusive device was powered by 12 VDC primary power for use with the new, emerging standard 12 volt auto batteries. I have only seen a photo of one, I have never seen one in the wild.
I know it’s considered Blasphemy to use any military radio with “non-issued” accessories like this. However, I use this radio pretty routinely at campsites and I needed something “12 Volts DC” and practical when not going the “entirely military experience” route. The PP-2684/GRC-109 AC power supply can also run from 6 VDC but it is big and heavy and also requires a big, 6 Volt battery; somewhat rare these days. Then there is the vibrator hash noise as mentioned earlier. Not practical for my ops. So here we go!

UPDATE: Sometimes you can’t find a particular piece of useful or interesting surplus military gear, so then you have to build your own. When complete, I will integrate both the TX and RX 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 the receiver power supply.

To invent … you need a good imagination. And a pile of junk.
– Thomas Edison.

GRC-109 DC-DC power supply beginnings N6CC

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 unobtanium connectors are a challenge – I’ll go with cable adapters. The case is a spare case casting for a GRC-109 transmitter. There will be enough room inside to include a GRC-9 transmitter B+ power supply off in the future as well. First I would have to find an elusive GRC-9 female chassis connector to mount on the side of the box.

Power Supply Initial Layout musings

Power Supply Initial Layout musings

Above: Will everything fit? Some initial layout planning. Almost everything that went into this power supply except for the case, PVC pipe fittings and some molex connectors came from the junk box (whose parts availability drove the design). Total parts cost: about $20 but about 3 weeks of design, fabrication and testing which is the “expensive” part.

GRC-109 DC Power Supply

GRC-109 DC Power Supply

Above: Yes, it all fits, with room to spare for the future HV B+ supply for the GRC-9 as well.

GRC-109 12 Volt Power Supply - N6CC

GRC-109 12 Volt Power Supply – N6CC

Above: The prototype GRC-109 power supply powered by 12 Volts DC. The standard issue cover screws into those corner holes for transport and storage, just like the other GRC-109 components. It provides 1.40 VDC regulated filament power, 6.3 VDC, 102 VDC and 425 VDC. It is built around custom-designed, high frequency ferrite core transformers and the usual standard power supply parts. A basic “brute-force” design….No fancy “SMPS” technology here – that stuff hurts my head.

The design is based entirely upon the magnetics of the HV transformers, and that NOS core material and form factor are what I had available.. As a consequence, replicating this supply would not be simple – it strongly depends upon these transformers and their resultant frequency of oscillation, turns ratios and efficiency. The final design is the result of much experimentation beyond the “math”.

So that project is coming along. I have built the power supply into the former GRC-109 transmitters’ cast aluminum case and then installed the receiver PS module inside as well. The 12 gauge power cable with Power Pole connector rolls up and stashes inside the screwed-on protective cover. It is working well – the transmitter delivers 13 watts of RF into the antenna while powered by this supply and it sounds very clean, T9. I have included a small fan to keep it cool for any further expansion for the GRC-9 transmitter B+. It is not needed now, it runs only slightly above ambient temperature.

GRC-109 12 Volt Power Supply - DIY Model

GRC-109 12 Volt Power Supply – DIY Model

Above: The DIY power supply powering the transmitter and receiver. The RX and TX supplies are electrically independent so I can just monitor with the receiver when no transmissions are necessary – saves battery power before the Comm Window time arrives. With both supplies running and the transmitter “key down”, it draws under 5 amps. With the receiver alone, it draws 800 ma. So with the low duty-cycle of CW, my little 12 volt garden tractor battery will power the system for at least a week of casual field ops – even if I don’t bring the solar panel. As a bonus, the GRC-9 receiver can also be directly powered by this supply simply by plugging in the GRC-9 battery cable into the front panel receptacle. The GRC-9 transmitter upgrade inside is next on the list.

12 Volt DC-DC Power Supply running the GRC-109 Receiver

12 Volt DC-DC Power Supply running the GRC-109 Receiver

Above: The DC-DC power supply can run the receiver and the transmitter simultaneously. While using a small Gel Cell as above, the transmitter is powered by the G-43 generator with the battery only powering the receiver. That small battery will power both but you could not make many long transmissions before the little battery would need recharging. Solution: Use a larger battery like a Deep Cycle garden tractor or marine battery instead. With a small solar panel you are operational indefinitely. OK, lets try that….Off to Military Field Day 2014.

Solar Powered GRC-109 in the Field

Solar Powered GRC-109 in the Field

Above: The first power supply shakedown operation in the boonies. Here running a small 20 watt solar panel charging the garden tractor battery. This powered the GRC-109 with the new DC-DC power supply for a 4 day operation in the mountains. This setup would run a forward operating base indefinitely, its pretty quiet – and easy to set up and transport while tailgate camping.

The system worked well, plenty of capacity. I worked a bunch of guys in California on 40 meters CW during the day; 500 mile shots are no problem. Just a hint of power supply oscillator harmonics up in the HF band around 25 Kc apart and they drift around a little until the PS warms up for a few minutes – then they stay put – and are not a bother. Not much above the noise level. A snap-on ferrite choke on the 12 V power leads drops it considerably – but I forgot to bring that…No problem….

The long orange power cord to the panel allows me to move the panel into the sun without having to move the equipment. I also brought along my homebrew charge controller with its metering capability. Not really needed since the 1 Amp full sun panel cannot overcharge this battery. But the metering makes it interesting…

GRC-109 Solar Powered in Camp

GRC-109 Solar Powered in Camp

Above: Another miserable day in the mountains…..Elevation 7550′ AMSL about 40 miles north of Yosemite National Park; mid June.
Steaks and trout cooking…..Time for Radio Silence.

Night Ops:

Night Ops Deployed: Field Day 2015

Night Ops Deployed: Field Day 2015

Above: Working Field Day 2015 with the GRC-109 and the new 12 VDC power supply running off the garden tractor battery. Lots of contacts with the “by the book” 100 foot inverted L wire antenna on the transmitter, a 50 foot horizontal wire for the receiver. That’s the TRC-77 in the ALICE pack off to the right.
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…..

MK-833/GRC-109 Maintenance / Spares Kit

MK-833/GRC-109 Maintenance / Spares Kit (MOD)

Above: The Maintenance Kit, Electrical Equipment MK-833/GRC-109(Mod). This kit with its watertight snap-on lid contained spare parts for the radio set. The original set included a complete set of spare tubes, fuses, lamps, screwdriver, needle nose pliers, TL-29 knife, 2 wrenches, 6 antenna insulators, power 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. This box is unmarked; probably of CIA RS-1 origin.
My kit is not yet complete – still working on finding some of the original parts including the original insulators, ground clamp, pliers. However, I have modified the contents by adding a few experience-gained accessories; this kit will keep me going for a long time. The “Mods” include power adapters, jumpers, external key/headset adapters, an official USGI Memo pad with “Skillcraft” ball point pen, tape, coax adapters, wire antennas, a small “amplified” speaker, and a set of laminated schematics etc. Like the radio sets themselves, this case could be buried in a swamp indefinitely – good sturdy gaskets and firm snap closures. This kit will also support a GRC-109A and RS-1 sets; this kit will also support an RS-6 set by substituting the appropriate tubes..

GRC-109 Maintenance Kit with accessories

Maintenance kit with some operational accessories packed out, ready to go.

The T-784/GRC-109 Transmitter:
One unfortunate problem is that the receiver is somewhat starved for antenna signal when a common antenna is routed to the receiver through the transmitter during “key up”. (The CW key contacts “short out” the receiver antenna signal to protect the receiver on transmit; this to enable full “break in” – QSK – operation and especially to keep things simple with the use of a single antenna.) However, a quick look reveals that the receiver antenna coupling capacitor in the transmitter (C-14, an 18 pf silver mica) is much too small to couple significant common antenna signal to the receiver (particularly at the lower frequencies). Increasing it to say, 500 pf or greater would make a definite improvement. However the transmitter circuit cannot tolerate this increase since that same capacitor is in parallel with the pi-network variable loading capacitor when the key is depressed – completely de-tuning the impedance matching pi-network. A big capacitor won’t work.

T-784/GRC-109 TX Schematic

So that 18 pf value was a design compromise – a small enough value so that it doesn’t overly constrict the transmitter antenna matching range with a fixed capacitance – but big enough to pass SOME antenna signal to the receiver. As a secondary issue, the TX output pi-network also loads the receive antenna circuit noticeably during key-up. It presents a “low” impedance path to ground in parallel with the receiver, therefore a signal loss. (“Suck Out” is the layman’s term for this effect, whatever the heck that means. It’s just a passive circuit network branch.)

This component/network compromise was probably viewed in the context of the overall “systems design” for these radio sets. On operational missions they would most often be receiving a transmission from the “Base” station – which had big antennas and was running a high powered transmitter like the URC-32, GRC-19, GRC-106, FRC-93 etc. On tactical operations, those should produce an adequate signal to the GRC-109 receiver even with the above losses.
Also, getting the transmitted information OUT from this long range Recon team would generally be more important than getting information IN to them.

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. Modification by installing an internal relay or a PIN diode switching circuit would be simple, but I chose not to go that route. 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 for casual Ham operations but it takes a little more setup time, generally not a good solution for a fast moving tactical unit..

Another ‘109 transmitter oddity is the placement of the B+ HV feed (via RFC L-9) and the DC blocking/RF output coupling capacitor (C-13) on the antenna end of the pi-network inductor. This places HV B+ on the Pi-network inductors and switches. Those are “normally” placed at tube-end of the pi-network. Wonder why the designer did that..

The transmitter crystals can be on a fundamental frequency or doubled/tripled for the higher frequencies.  Multiplication comes at the expense of power output however.  No mention of this in the manual.  As an experiment, I tried (successfully) to drive my transmitter with a Heathkit HG-10 VFO to see if it would work.  More details on that experiment here: In a pinch, when your Comm Window approaches and you can’t find the right crystal, this will work pretty well at your Base Station.

HG-10B VFO driving the RT-3 Transmitter

HG-10B VFO driving the RT-3 Transmitter

Above: Driving the CIA’s RS-1/RT-3 transmitter with a vintage Heathkit VFO on 40 meters. This will also throw off enemy SIGINT intercept – they will detect the slight drift and deduce you are not using a crystal-controlled RS-1/GRC-109. You must be someone else…They are everywhere Tovarish! Could come in handy… Hi Hi.

The GRC-109A model uses the “snap hasp” method for connecting the cast aluminum covers to the beefed-up radio cases. 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 snap hasp closure was likely provided in the “A” model based upon user feedback from fast moving ground units that had to set up, transmit their traffic, repack quickly and then relocate while in the field. Maybe that hasp modification was faster but it caused more unintended consequences. The plain GRC-109 also fit inside an ALICE pack better.

GRC-109A Carrying Handle

Above the spring-loaded carrying handle of the GRC-109A. The “A” model units seem to be particularly dense – small AND heavy. The larger 109A cases add a lot of weight to the basic GRC-109.  The handle comes in, well, handy.

RT/D-3 and GRC-109A transmitter size comparison

Above: A size comparison between the modified CIA’s RT/D-3 transmitter with the GRC-109A transmitter. Those hasp mounts, protective bosses and covers make the 109A appreciably larger, noticeable while trying to jam it into a field pack.  The RT/D-3  transmitter is the same physical size as the GRC-109 transmitter (T-784).  The RT/D-3 variant is the RT-3 but modified for the use with the GRA-71 code burst keyer.  This one is also labeled MWO-39 which adds an RF choke from the antenna PI network to ground. (safety feature in case the output coupling capacitor fails, putting HV B+ on the antenna.) Your Assistant Radio Operator will appreciate that.

A few GRC-109/109A transmitter “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.  While running 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 is then difficult to tune the transmitter by looking at the lamp – which isn’t glowing.  Some Internet commentators attribute this effect to “erratic operation” or “it won’t load some antennas”. Wrong.

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 10 watt transmitter is developing a high voltage in this situation.  The NE-51 breakdown voltage is around 65 volts peak, RF. This will glow with the above antenna since the input impedance to a 1/2 wave wire is greater than 400 ohms.  I also use this trick on my SCR-284 transmitter as well.  Handy.  (You can also facilitate tuning a high impedance antenna with a field strength meter such as an ME-61/GRC.) With low impedance antennas (like a dipole or a 1/4 wave wire) the installed #47 glows brightly when tuned. Carry spares….

Be careful, this transmitter will give your finger a memorable burn if you touch the antenna post or the lead protruding through the post while you are adjusting the nearby Tune control! Note the “Danger High Voltage” foil sticker on the GRC-109A transmitter pictured above. It has a red arrow pointing to the antenna connector. A lesson learned and acted upon!  Hint: Don’t push the antenna wire all the way through the post – halfway is just fine and you finger will appreciate it. Or….

Introducing the ThumbSaver 2000: Your fingers will appreciate it and you won’t compromise your hide site location with loud swearing when you zap your thumb.

GRC-109 Antenna Post Guard

GRC-109 Antenna Post Guard

Above: A simple guard made from a 3/4″ piece of 1/2″ I.D. soft vinyl tubing. Poke a hole in the left side for the antenna wire. The wire does not go all the way through the post, out the other side. Instant finger protection, especially in the dark. Thanks to one R.F. Burns for that idea.

R-1004/GRC-109 Receiver

R-1004/GRC-109 Receiver

The R-1004/GRC-109 Receiver:
They are extremely well-built. Mine is in pristine condition internally despite an external case that speaks of heavy military use. The environmental protection of this 48 year old equipment is superb, not even a hint of corrosion inside. Note the thick neoprene gasket around the front panel interface and the glyptal treatment on the screws that penetrate the panel to the outside. Like the transmitter and power supplies, the chassis is not MFP’d (moisture fungus proofed), a testament to the designers’ faith in the panel and control gasketing and silica dehumidifiers. This makes it easier to work on if you ever need to do any internal soldering (I haven’t). Also note the generous number of stainless steel front panel screws to hold it together. When opening one of these sets up a powered screw driver is your friend!

The R-1004/GRC-109 does not have an AVC/AGC circuit so you may have to ride the manual “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 (only 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.  That’s especially the case when using a separate receiver antenna. Then, you must turn the Gain control all the way to minimum to (maybe) produce a usable sidetone. (Large excursions of the Gain control can pull either the BFO or local oscillator a few KC’s.) 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 anyway.  Takes some getting used to – just “feeling” your fist via the key; that’s a training issue. But then again, you are using the GRA-71 Burst Keyer to send your operational traffic aren’t you? Then, a non-problem.

The receiver IF bandwidth is 9 KC at the -6db points; broad but adequate for its intended purpose on CW, sounds good on AM.  For an operator working under pressure, tuning for the target transmitter does not have to be precise to get the job done.  On 40 meters the dial tuning window “indicator” line is about 9 KC wide. Sort of a graphical representation of the bandwidth that you will be receiving!

The receiver has a single “Gain” control. This control varies the grid bias and hence the gain of the RF amplifier and the first and second IF amplifier stages. The AF amplifier operates at a fixed gain setting. For a simple receiver, this needs to be understood as a compromise where separate RF/IF amplifier gain and AF stage gains are independently variable as in the GRC-9 receiver for example. So operationally, you may have to turn the Gain control high enough to hear a weak signal but in the process cause the signal to now over power the BFO injection in the detector circuit. It’s a tradeoff and part of the “character” of the set. I wouldn’t want to try to compare it with receiver technology of 60 years later. But then again, the new gear wasn’t designed to be buried in a swamp either.

If you want to go the unauthorized “luxury” route (or to put on a demonstration for uncleared visitors), use the receiver to drive a simple “amplified” speaker with its own Volume control.  Then you can adjust the Gain control for best reception and detection performance. Then vary the speakers’ amplifier volume control to an appropriate level. While “unauthorized”, this simple combination makes a major improvement in receiver “system” performance.

Comm Center, Forward Operating Base (FOB) “PIGOUT”
Above is the basic field setup providing us with reliable comms from a very remote off-grid location. The TX and RX were 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…. Powered by a handy Marine who happened to be in the area……

Field Ops with the AN/GRC-109

Above is the same system in action, as used to work WA6OPE on 7050 KC at 1300 Local, 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.

Refueling G-43 Generator

Refueling G-43 Generator

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

Young Marines Training: GRC-109 Radio Set

Above: Demonstrating the GRC-109 operation to future leaders 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 initials 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, nights/days, fed by a common coax works extremely well and is simple to get up.

Sending the daily SITREP

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. I can come up on LOTS of freqs…..

GRC-109 Operating Position at MRCG Camp SLO Meet, April 2012 N6CC

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 (OK, remote) 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.

By the way, the receiver local oscillator tuning employs “high side” injection. The tuned LO is 455 KC ABOVE the desired receive frequency (which you would never know by reading the manual; it does not mention that). So in using a crystal to set the receiver operating frequency, it must be 455 KC higher (or lower) than the desired working freq. In either case, the mixer output is the IF frequency, 455 KC.

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.

GRC-109 and Command Set at Forward Operating Base N6CC

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.

GRC-109 at Forward Operating Base Shangra La

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.

OP at Sonora Pass California

This weeks’ mission: establish Road Watch 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.

Rigging the PRC-74 dipole antenna to the GRC-109

Above – The Assistant Radioman 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 – and they are of the same era.  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 AS-1722/GRC-109 100 foot “hank” wire antenna as an inverted “L” and then pound in a ground stake.  It will work pretty well. (as an example of grounding, here is a PRC-25 grounded with an 18″ aluminum guy line stake.)  Sand off the paint beforehand.  Dig a fist-sized hole, fill it with water, pound the stake all the way in.  Keep it wet. This is more or less right out of “the book”. It works, but a bunch of long “radial wires” will work much better – more RF into the target receiver.

PRC-25 Half Rhombic Chassis Grounding

PRC-25 Half Rhombic Chassis Grounding

Above: Again it’s advisable to ground any radio, essential at HF frequencies when using a non-symetrical antenna such as a long wire or Inverted L. But here, a PRC-25 running a Half-Rhombic on 51.0 MC. Run the excess ground wire out directly under the antenna wire, preferably all the way to the far end termination resistor.

TRC-77 HF Radio ground stake

TRC-77 HF Radio ground stake

Above: A similar tent stake ground, in this case for a TRC-77 HF CW radio. You would do the same thing with a GRC-109. With a “Bush Antenna” (a semi-random slant wire), ground radials are essential for radiation efficiency and consistent antenna tuning. This ground stake was also necessary at this site to keep RF off the radio chassis. Simple, add a few packets of salt in the hole, keep it wet. Not great, but adequate.

PU-181 Gas powered generator

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. The TM states that it will run for 7.5 hours at the full 300 watts output on one tank of fuel. When powering my usual military radio gear in the boonies running casual operations it will go for over a week on a single tank. Fill it up and go….no need to bring the Jerry can. 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.

Tuning the GRC-109 in the field

Above – The team’s Assistant Radio Operator tuning the transmitter. Note the separate receiver wire antenna heading up into the trees.

GRC-109 ready for operations

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.  My buddy 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 via a parallel path upon key down.  It is “grounded” by the power supply connectors anyway.  Thin air at 8100 feet can cause these things!

Forward Operating Base Comm Center

Above: I love the sound of CW in the mountains!

GRC-109 Operated from my transit case

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.

FOB Wendy GRC-109

FOB Wendy GRC-109

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

GRC-109 Creekside with battery powered receiver

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.

GRC-109 at Camp San Luis Obispo Crypto Exercise

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:







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


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.

UPDATE August 2013:
A recent field Op, this time at LZ Lamb Chop in the Sierra Nevada mountains near Yuba Gap CA. We were running the GRC-109 and a PRC-47. The weather and chow was great and we had excellent comms with many friends and new hams that stopped by the frequencies we had planned.

GRC-109 station at LZ Lamb Chop

Above, the combination CW station, barracks and night stand. I was primarily running an 80 meter dipole on 40 meters for the transmitter and also an Inverted L T/R antenna. The alarm clock helped us to make comm windows (schedules) on time among the usual camping activities. I had used both the J-45 Knee Key and also the built-in key on the transmitter which I also like. (When using the set at home, and for long “rag chew” sessions I sometimes use an ancient Hammarlund HK-1B keyer with a Vibroplex paddle. Much easier on the arm!)

We tried running the ‘109 from my friends’ Samlex 600 watt sine wave inverter driven by a 12 volt deep cycle battery but the hash noise was too much. We then switched to his Honda EU-1000i generator but its radiated ignition noise was terrible despite it being at the end of a 100 foot extension cord laid at right angles to the antennas. The generator has a plastic shell – no shielding. It was connected to an expensive common-mode noise filter at the generator end. But we worked lots of stations through the noise.  I had also used the DIY DC-DC convertor that I had built for the receiver for casual band-cruising.  Powered by a 12V gel cell, it worked fine and was quiet. Perfect for late-night SWL’ing without the noisy generator…Seen below.

GRC-109 / R-1004 powered by DC-DC convertor

Above – the CW station on gel cell power for the receiver. I had also used the little Radio Shack amplified speaker on the output so my buddy could copy along in the conversations.

Antenna-wise we were also using an interesting antenna in addition to the low dipoles. My buddy brought along a wire antenna captured from the Viet Cong by the U.S. Marines in Vietnam, circa 1968. This war souvenir was set up to be an inverted “L” with about 10 meters of vertical feedline and 33 meters horizontal. Below is the insulator at the junction:

Viet Cong Inverted L Antenna

This antenna was made with rubber coated stranded wire and the insulation was mostly falling off during the intervening years. The insulator was broken, as was the end insulator. The “apex” insulator splice seen here was secured with seizing wire made from enamel coated magnet wire. The radio end was a simple open spade lug. We rigged it as an inverted L as it was most likely intended. It worked well with the GRC-109 on 40 meters but our 15 foot high dipole on 60 meters with the PRC-47 worked a little better over the NVIS paths we were working.

This antenna was captured from a Viet Cong or North Vietnamese Army unit working in the “Rocket Belt” around Da Nang. He doesn’t know what radio it may have been connected to at the time. I think it is probably the issued antenna for the ChiCom Type 102E set. The wire looks identical to the antenna wire shipped with the ChiCom surplus Type 102E sets formerly available from Red Star Radio. After we initially connecting it to the GRC-109 receiver we listened carefully for any faint, chirpy 5 character cipher groups using cut numbers, but alas, they had long ago faded away. Long ago and far away……

Viet Cong Inverted L Antenna

Viet Cong Inverted L Antenna

Above: The vertical-horizontal junction of the Viet Cong Inverted L antenna. A nylon halyard going off to the right from the broken insulator.

For more information about the field antennas used with the GRC-109, take a look here Portable Field Antenna Kit

One can learn a lot about how the GRC-109 and its relatives performed under combat conditions by taking them to the field and using them today. I’m a believer…….

Di Dah Di Dah Dit

Your observations, inputs, corrections and comments are most welcomed..