AN/GRC-9 Radio Set

Updated 4/22/13:

US Marines of a Tactical Air Control Party with the First Marine Division in combat at the Chosin Reservoir operating a GRC-9 transmitter-receiver.  Note the weapon cleaning rod likely being used for a ground rod.  GN-58 hand cranked generator, cold weather, possibly watching Marine Corps Corsairs rolling in on target:  NK or ChiCom troops danger-close.  Hopefully it got REAL HOT for the Reds in short order. Field day of the highest order, not fun.  But I bet it did the job…    The Marine holding the T-17 is likely a pilot from the supporting Marine fighter squadron. The Marines found that this type of assignment produced the best air-ground, close air support coordination possible.   Thanks guys.    Official USMC Photograph.

Later on……”With voice transmissions ruled out by distances, communications specialists must rely on continuous wave radio operation, using the International Morse Code.  They must be able to receive and transmit at the rate of 18 words per minute, perform maintenance up to Third Echelon and even build a working set out of parts at hand.  Other team members must be able to work at least five words per minute and know how to set up and operate a radio.  Workhorse of the Special Forces is still the dependable Angry Nine, officially the AN/GRC-9.” Special Warfare U.S. Army, Chief of Information, U.S. Army 1962.

Left:  The “GRC-9″ at work with U.S. Army Special Forces and Vietnamese irregular forces.  Note the taller G-43 generator had replaced the GN-58 in this instance*. Official Photograph, U.S. Army 1964.

 

 

This frame is from a Signal Corps film following a Special Forces patrol in Vietnam. The filmer or the person that entered the description in the National Archives file mis-identifies the radio as the GRC-109.

Below is my “GRC-9″ set up on the Pacific beach at Spooner Cove near San Luis Obispo CA during less stressful times.  (Actually, it is a GRC-87 – do you know the difference?*) We were running “Coastwatcher Ops” and transmitting Bikini Reports back to a TCS set at Camp San Luis Obispo acting as Net Control.  This was during the Military Radio Collectors Group meeting in May 2010.

(*The RT-77/GRC-9 receiver-transmitter when deployed with the G-43 generator, LS-7A (or LS-203) speaker and the ME-61/GRC field strength meter is defined as the AN/GRC-87 “system”. (TM11-5820-453-10, 10MAY1963 refers) )  If you’re keeping score.

The distance from here to KG6UTS at Camp SLO NECOS was 9.2 Miles over hilly, rocky terrain.  From here to N6IHU was 3.3  miles and N6IHU to Camp SLO was 5.8 miles.   N6IHU was running another GRC-9 in a portable configuration however he was using the DY-88 Dynamotor power supply.  Under the conditions at that time (appx 1000 hours local) the signal to noise ratio of received signals was 2 to 3 times better on the whip than the AT-101 wire which surprised us.  It was running approximately northwest, broadside to Camp SLO, averaging about 6 feet off the sand.  Comms with the 15′ whip antenna were Q5.  I didn’t note the FoF2 critical freq at that time to see if the low wire would work in NVIS mode under those conditions.  Apparently it was lower than our 3885 freq and/or the D Layer absorbtion was very high then.  We ran the standard ground radial wire array, G-43 hand cranked generator and a battery for the receiver to save the “power supply”.  The TCS was running a 30 foot inverted L and N6IHU was running the standard whip antenna.  This setup would have been a very workable tactical circuit. Photo: Tim Sammons

Below is a typical mountain top campsite to cover all circuits. There is the GRC-109, GRC-9, PRC-47 and the mobile GRC-9 all on-line. However, looks like the flash caught the Midwatch off guard. Zzzzzzzz.  Good thing the Sergeant wasn’t around!

Below is a shot of our Perimeter Defense Force checking out the Company Command Post.  Note the GRC-9 AC Power Supply built in the .50 Cal Ammo Box on the ground.  Provides all voltages from 120 VAC.

Above: The GRC-9 was operational at the Military Vehicle Collectors of California April 2013 Rally at Camp Delta. A Battalion Communications Center capable of handling comms relay between any possible Time Warp from 1944 through the 1970′s. We worked lots of stations on 40 meters CW with the GRC-9 and its’ simple whip antenna. Always a hit with the visitors.

Above: Later that night…..

Don’t let this happen to you! Do your PMS and then double-check everything!

Above: QSL Card from the USS Pampanito SS-383, normally moored in San Francisco near the Golden Gate bridge. I worked their ham station, NJ6VT aboard the sub on CW with my GRC-9 from our Forward Operating Base in the Sierra Nevada mountains. Her wartime Navy call sign was NJVT.

Below is a shot of the GRC-9 in the field using the .50 caliber AC power supply. “You have a strange rushing sound in your Transmit audio”….Yup…. This is the setup I used to work the USS Pampanito submarine on CW during a “Museum Ships On The Air” weekend. Better than 150 miles on 40 meters during the day.

Below is another shot while sending Ditties from FOB (Forward Operating Base) Margarita….The little AC power supply in the .50 Cal ammo can makes it convenient to work in camp. Especially when you bring the generator to run the Blender anyway!
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Below: Would you believe a solar-powered GRC-9? Been there, done that. Here we are set up in the mountains west of Lake Tahoe at OP COMMANDO, monitoring kayak traffic 2000 feet below us on the North Fork of the American River. Panel charged the deep cycle battery which powered the sine wave inverter that powered the ammo box power supply which powered the GRC-9. Inefficient as hell but it worked!

Below is another shot of that same position – we also had a PRC-47  going on CW and LSB as well. There is the wreckage of a C-46 Commando somewhere within a mile of this location.  Very dense forest in here.  It’s on our list for a search expedition. This spot will make for a very good base camp.

Above: Mounting my other GRC-9 in the back of the old Bronco makes it pretty convenient while camping. I can check into the Saturday night West Coast Military Radio Collectors Group net on 3985 KC AM, even from my sleeping bag if it gets cold. I usually run 80/40 meter coax-fed dipoles but sometimes just a quarter wavelength wire or the MP-57/MS vehicle-mounted whip depending upon how long I plan to camp in one place. If the racoons wake me up at 0345 I can check the propagation worldwide without getting up.

The Bronco is pretty cramped with camping gear so I had little room for a huge DY-88 dynamotor power supply. So I built a small transistorized power supply that runs off the vehicle 12 Volt battery; with the little supply sitting under the passenger seat. It works well and is more efficient than the dyno but I miss the Dyno Whine during Transmit !

Above: The GRC-9 at work down in the Commo Bunker sending out the nightly SITREP at Zero Dark Thirty.
(BTW, it’s an old military phrase that has been around since clocks were invented and the troops had to get up early. Then the Hollyweird crowd discovered it and was so enthralled with it they named a movie after it…. Same with “Hurt Locker” but I digress…Those people need to get out more often – yeah, right.)
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A note on the GRC-9 homebrew power supplies discussed above: I have gotten many requests for the design of the AC and DC power supplies that I have built.

As we know, the GRC-9 requires a number of different voltages from the power supply. 580, 108 Reg, 6.3, 1.5 ……I was able to build supplies around junk box parts I had on hand, but the design is entirely dependent upon the kind of transformers you can get – it is central to any design you could make. It completely defines the circuit specifics you will need. The AC transformer I used in the Ammo Box supply is from an old oscilloscope PS, I think the transformer is a Stancor R-50C if I recall – long obsolete. It had lots of different voltage windings. The DC supply is built around a transformer from an old Heathkit mobile transceiver DC supply that was scrapped – and it also had a lot of winding voltages I could work with and adapt. Especially the all-important primary and feedback windings needed for a 12 VDC transistor power oscillator.

Without either of those transformers my design would not be useful to anyone trying to replicate them. That said, however, the designs are otherwise straight forward and follow the ideas in any of the older ARRL handbooks for providing those voltages. I used adjustable LM-350 voltage regulators for the +108 and 1.5 volt supplies. I chose to regulate the receiver filament voltage to protect the tubes and I also regulate the receiver B+ in the supply. Consequently, the VR105 (OC3) tube in the GRC-9 does not “fire” with externally regulated +108V applied and this works well.

Unfortunately no one makes suitable HV power supply transformers anymore in the “transistor age”. Especially DC-DC HV converters. You must work with what you can find – and that took some digging….
And that was part of the fun……
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Problem areas:  Both of my GRC-9′s have been very reliable, they have all the original tubes and capacitors and I have not needed to make any repairs on them despite 20+ years of frequent use, both mobile and portable. The only item needing attention is the bias battery used to keep the receiver 3Q4 pentode AF power amplifier tube properly biased. (The receiver will work without a battery installed, however the audio will be somewhat distorted and that tube will draw excessive plate current as a result of no bias voltage – not good). For that application, I use three 1.5 volt cells from an ordinary 9 volt battery. Left in series via the spot-welded stainless steel jumper straps, they make a good replacement battery of -4.5 volts. A bit of heat-shrink tubing or tape, and a salvaged battery connector, it fits in the original battery holder.  That battery will last for years – the shelf life of the cells.

That said, one of my GRC-9 receivers had an annoying, intermittent receiver “cut-out” problem that occurred while turning the tuning knob. The receiver would just quit, sometimes preceded by a scratching noise while the knob was being turned. I assumed it was debris between the tuning capacitor plates causing that (high impedance) stator circuit to short to the grounded rotor plates. I tried several times to blow the plates clean with a micro duster – that seemed to help – but not permanently – sometimes the problem re-appeared at a different knob position. On the right track.

It started doing it again! I pulled the receiver and removed the shielding covers and blew it out again. Kinda worked. Upon CLOSE examination with a high-magnification eye loupe, I saw a few tiny fibers protruding off the rotor plate but they were not positioned to touch the stator. Ah Ha !! Tin Whiskers. They were about 2-3 mm long, and looked to be about the diameter of spider web silk – if you can get the light just-right to even see them. Maybe a couple of microns in diameter.  If they are here, they are probably elsewhere in the capacitor assembly. They are apparently strong and stiff enough to withstand the micro duster gas blast in some areas that were hard to get to.

Tin whiskers are a well known problem.  They have greatly compromised all kinds of electronics since the environmental-cases started banning lead from tin-lead solder; and apparently even before that. This is the “RoHs” initiative started by the EU and then adopted by the US and others in a knee-jerk reaction.  “A planet completely free of any and all risks.”  But just a little bit of lead alloyed in  significantly inhibits the formation of these tin crystal “whiskers”. Tin-lead alloy solder does not have this problem; lead-free solder and native tin plating DOES. Some really interesting physics going on here….(If you have done any soldering with the lead-free stuff, you know it does not work very well as a solder, future whiskers notwithstanding).

My radio was made well before that decree started causing short-circuit problems, but the plates of my variable capacitor are apparently tin plated. A thorough “cleaning” with a slice of a business card slid inside each rotor-stator plate gap knocked off any other whiskers that were causing the problem with this set. Back in operation, no more receiver drop-outs. (By the way, the problem section of C7 was the local oscillator tuning – the LO stopped at certain rotor positions, thus killing the receiver).

Take a look at the tin whiskers on this variable capacitor frame. (Obviously not a GRC-9 capacitor – but you get the idea!)  Holy crap! (Photo: NASA)

 

 

 

 

 

 

According to NASA, at least 10 satellites have been lost and up to 7 nuclear power plants have been partially shut down due to tin whiskers shorting out critical circuits. Is the “cure” worse than the problem? Look at that photo and extrapolate – you be the judge.