PRC-6 Radio

UPDATED 4/29/2023

Beginnings of some notes on the hand held Radio Set AN/PRC-6 FM radio.  There is lots of information on the Web regarding these radios so I will just discuss general observations and my experience in using this particular set.
The AN/PRC-6 portable radio set, AKA the PRC-6, AKA the “Prick” 6, AKA “The Banana Radio”.

The basic receiver-transmitter unit is the RT-196. Incidentally, the manual does not refer to this set as a “Walkie Talkie” – a term applied to the SCR-300.  It does call it a “Handie Talkie” – a term applied to the SCR-536.

Basic Characteristics:
Frequency Coverage: 47 – 55.4 MC, crystal controlled transmit and receive on 1 preset Channel
Frequency Modulated (FM) voice
Technology: 13 miniature vacuum tubes in circuit
Transmitter deviation: 5-17 KC nominal
Power Source: BA-270/U battery (portable) 1.5, 45 and 90 Volts
Battery life: Depends upon transmit-receive ratio in use.
Power Output: 0.25 watts
Selectivity: 70-90 KC at the -3 db points
Sensitivity: Less than 1 microvolt. There is a Volume control, no Squelch function is provided
Weight: 6 pounds with battery, as carried
Planning Range: 1 mile

Above: The basic radio, what you see is what you get. Simple in operation it includes only a function switch, a volume control and a Push-To-Talk button. It includes a pressure equalization valve on the bottom to assist in opening the case if it had been previously opened at high altitude, or to vent battery gasses. The case cover seal is very effective. The environmental protection is good, the case is made of magnesium, the tape antenna is forgiving. At 6 pounds with battery, it’s reasonably light for what it provides from the available technology back in those days.

The PRC-6 was designed to replace the WWII SCR-536 (AKA the BC-611) “Handy Talkie” which operated on HF frequencies using amplitude modulation. The realization during WWII that VHF/FM was a better mode for local tactical comms ultimately drove the requirement for the PRC-6, a VHF FM set (and the SCR-300 before that). Although they both use vacuum tubes, the PRC-6 was a significant technology jump. Note the differences in appearance:

The use of magnesium for the PRC-6 case is interesting. Certainly lightweight and easy to cast, it could also become its own Thermite grenade in the event of enemy capture. Just get one corner hot enough and off it goes. The GRC-9 and GRC-109 also have this “feature”.

This particular example was made by Raytheon under Contract 3319 Phila 1952, serial number 49843. I bought it NOS from Fair Radio around 1977 for $18, it included a crystal for 51.0 MC. All wear marks, dings and scrapes are mine from occasional use since then. This one had a weak microphone output so I replaced it at some point. Otherwise all original. Fair Radio Sales also shows replacement tubes available (July 2018) if needed. (I’ve never had to replace one…)

The set has provision for an external H-33(*) handset which can be selected by moving the Function switch to “EXT” for external handset. The “INT” position connects the built-in mic and earphone. The installed microphone element is carbon as is the element in the H-33 handsets.  Sometimes they need a good mechanical “whack” to loosen up the granules if they have sit for awhile.

It has provision for an external DF loop antenna via the BNC connector. This connector was for primary use with the AT-339 Homing Antenna that was also used with the PRC-10 radio.  Incidentally that loop is very effective with the PRC-6 in fox hunts at MRCG events.

An external communications antenna could possibly also be used if longer range was needed.  The manual is silent on that application but I am sure it was at least tried by a GI seeking longer ranges. I am not sure the coupling impedance to that connector will match a “50 Ω” external antenna.  The supplied antenna is the flexible steel tape type which can be stowed under the case clips when not in use.

I believe this was the first use of this novel antenna type. Pretty hard to break, unlike the telescoping whip found on the SCR-536/BC-611 Handy Talkie.

Above: The PRC-6 with an eternal H-33/PT attached, function switch on EXT. The handset PTT button actuates the transmitter. This was a good idea. It gave the infantryman the ability to use a weapon or to perform other tasks hands-free, with the radio slung over his shoulder or inside a field pack.

The handset could be hung on a suspender loop or buttonhole on his uniform. However, carrying the radio slung across your back is a bit painful – those case clips always seem to find your backbone.

The design work on the PRC-6 was started in March 1945 and then developed in the late 1940’s as a simultaneous replacement for the SCR-300 (BC-1000) and the SCR-536 (BC-611) as an infantry company radio. In that service it was probably intended for communications between an infantry company commander and his platoon leaders. It continued the leap to FM for tactical communications something the SCR-536 could not do.

With appropriate crystals installed for 47-48 mc overlap, the PRC-6 is interoperable over 6 channels in the “Infantry” radio band with the SCR-300.  Also interoperable with the GRC-3/RT-68 (series), the PRC-10 and the early aircraft FM sets such as the AN/ARC-44 and 131. Later sets such as the PRC-25 and PRC-77 were backwards compatible with it when on the same frequency as the crystal channel.

I am not yet sure of when it entered into widespread US Army service. I have an Army field maintenance manual, TM11-4069 which is also the US Air Force Technical Order TO16-30PRC6-5 dated June 1952. I have seen two photos of its use in Korea in 1953 with the Second and Seventh Infantry Divisions.

Beyond that, I don’t know when it arrived in Korea, with which units or in what numbers. Like the PRC-10 there is little information readily available on its early operational history so more research is needed.

Above: Jean Pierre Van Ick, one of the 3000 Dutch soldiers cross assigned into the US Army Second Infantry Division in Korea operating a PRC-6 in the field with UN forces.

“OPERATION OF RADIO SET AN/PRC-6 UNDER COMBAT CONDITIONS. – AN/PRC-6 radio set has proved to be eminently suited to the operations of an infantry battalion under a wide variety of difficult conditions. In range of transmission, frequency and in durability, it has proved superior to all available transceivers.

[However] The flexible antenna AN/PRC-6 has proved most unsatisfactory under field conditions. The bottom section of the antenna splits even though extreme care is exercised. Heavy taping of this section prevents splitting but destroys flexibility. The push-to-talk button does not stand up under heavy use. The case is not waterproof. (Command Report – 224th Inf Regiment – May 53.)” Korean War After Action reports.  (Reference 103.)

The PRC-6 was used into the early 1960’s in Vietnam; there are many photos online of it being carried and used by US and South Vietnamese forces. I saw a captured PRC-6 in a Vietnamese military museum in Saigon in 2012. I’m sure the Viet Cong and North Vietnamese Army in the south put them to good use as well.

The US Army’s Reference Data for Field Radio Communications, ST-11-174, 1 June 1962 lists the PRC-10 Status as “Standard” B. Still issued in the system. That document also shows the PRC-6 and PRC-25 Status as “Standard” A, implying more routine deployment than the PRC-10. Standard “A” is the preferred item, Standard “B” is an acceptable item but no new procurements should be made. (Ref. 29)

The design was state of the art for miniature vacuum tube circuitry at the time. It is really quite compact with most of the internal volume taken up by the battery. In the below photo you can see the clean layout and the steps taken to make frequency changes something a local unit could accomplish unlike the more difficult SCR-536 frequency changes. All you would need is one new crystal and the purpose-built Channel Alignment Indicator, ID-292/PRC-6; or just a VTVM.

I have checked the alignment of mine on 51.0 with a VTVM – it does the job just fine.  The set issue came with an accessory CY-853/PRC-6 crystal box containing 42 crystals to permit its operating on any of these 42 frequencies within its range.  Channels were spaced 200 KC apart.  The receiver was crystal controlled; the transmitter oscillator was VFO based but locked to the receiver frequency via an AFC loop.  The receiver LO was 4.3 MC below the operating frequency; 4.3 MC being the Intermediate Frequency of the receiver.

TM 11-296 says that all the radios shipped from the factory (Raytheon) came equipped with 51.0 MC installed as a starting point.  The handful that I have seen all have 51.0 crystals installed. That is also true of the PRT-4/PRR-9 Squad Radio’s – again all that I have seen were on 51.0 and they are interoperable with the PRC-6.  With the short range capability of these sets, deconflicting comms among infantry units on the same channel in a battalion’s AO may have been workable.

Above: The circuitry module with the dust cover removed. There are 12 sub miniature pencil tubes and a larger Type 3B4 power amplifier output tube. The pencil tubes can be seen with their vacuum port tips held in place by the black rubber grommets. The various tuned circuits are contained in the orange plastic boxes which each contain a novel 2-digit counter mechanism to indicate the inductor slug position.

These are pre set against the tuning chart as a function of the operating frequency. A metering jack (lower left corner) permits measurement of each stage while its associated circuit is fine-tuned; there is a jumper to enable PA plate current metering. The operating crystal is in the lower left corner and there is a clip provided for a spare crystal.

Good serviceability design here. The tuning chart is “generic” to the PRC-6 and it is pasted inside the radio cover.

Also shown is the DC-DC converter module designed by the French for their PRC-6’s. This module is the same size and with the same connector pinout as the BA-270 battery and it gets its power from 9 regular BA-30 “D” Cells which mount inside. This is a really neat addition to the PRC-6 and it is very well designed. Uses common batteries rather than the custom BA-270 and it operates the radio with no inverter “hash” in the receiver or transmitter. Direct replacement for the BA-270. I have used jury-rigged packs of C Cells and 9 volt batteries to power the radio but the French supply is the way to go, get one if you can find one!

As is often the case, the US provides equipment like these radios to our allies to equip their forces and to enable interoperability with ours. As is also the case, our allies sometimes continue using this equipment after the US upgrades to the next generation technology. With an eye to economy, other owners of this radio used it into the “transistor age” which enabled small, efficient DC-DC converters like this one.

The French also built one for the PRC-10 and probably others as well. Smart. The Germans took this one step even further with the PRC-6 – they modified it to include 6 switch-selectable channels making it much more versatile, the PRC-6/6. They also built a single channel fully transistorized version in the original case. There also may have been a 180 channel variant.

Into the Boonies with the PRC-6:

Above: Forward Operating Base Hell’s Half Acre – a typical camping trip into the Sierra Nevada mountains. We were using the PRC-6 along with the vehicle mounted VRC-7/RT-70 on the 6 meter Ham Band. In mountains and dense forest like this it is good for maybe a half mile in the trees, many miles if reasonable line-of-sight paths are used. We were hiking around and testing its range limits back to the vehicle. It worked well and produced about the same range as our FRS walkie talkies. At only 25 times the weight! LOL.

But it was fun and gave us some idea of how they could be used operationally. (They get heavier the longer you carry them.) We were also running an RS-6 HF CW set from this location; both sets were from about the same historical era. We made several hundred mile contacts with the RS-6 on 40 meters on this Op. We also had a GRC-9 running in the back of the Bronco – the PRC-6 felt right at home!

Above: This was our OP at LZ Diablo, up on Mt Diablo east of San Francisco, 3260 feet AMSL. We were running range experiments with the PRC-6, the PRC-25 and the VRC-7/RT-70 mounted in the Bronco driving the stock AB-15/MS whip. My buddy was located on a rooftop in San Francisco 27 miles away and another guy 17 miles away across Carquinez straits near the Suisun mothball fleet, off in the haze in this photo. PRC-6’s all around plus another RT-70 across the straits.

We had solid comms between here and both locations over an optical LOS path with the PRC-25 and VRC-7/RT-70 on my end. We also had good comms with the PRC-6’s but they were right in the fade margin so moving around a few feet in either direction made a lot of difference. My buddies could not work each other due to significant terrain blockages between them.

On the path to the mothball fleet station (and after some kinks were worked out) I was able to work him quite well when I stood about a quarter wavelength in front of a chain link fence at the site. The metal fence worked quite well as a reflector that was basically facing my distant target. This with radios having a Planning Range of 1 mile. Take the high ground! Location Location Location…..

We also tried my 3×5 inch signal mirror to both locations. WOW! Bright Flashes! Lots of fun and lots of curious hikers getting educated on the capabilities of old military radio gear.

Above: Field Day Ops on Mt Diablo, 1986. My buddy and I were running a GRC-109, PRC-10 and a PRC-6 from this perch on the mountain. We ran the GRC-109 and the AC power supply for the PRC-10 from the PU-181/PGC gas generator seen on the right, background. Inverted “L” antenna on HF and working 6 meters FM simplex with the PRC-10 just using its whip.

Six meters was pretty quiet at night so we played with the PRC-6/10 pair around the mountain. We did make many contacts with the PRC-10 on 52.525 MC, the 6 meter calling channel. I don’t remember if we made any contacts with the PRC-6 after moving the QSO to 51.0 MC but we probably tried anyway.

Above: Fun Fact: The same site showing the AB-85 mast we set up for the Inverted “L” and also the clear view from here. Again, playing with the signal mirror we were able to flash a passing P-51 Mustang (either “Kimberly Kaye” or “Merlin’s Magic”, I forget) flying out of the Livermore airport. He saw us, circled around and made a LOW pass overhead, blasting by our position. We waved. He waved back with his wings then quickly disappeared. 10 minutes later the Park Rangers showed up asking us what was going on. “Oh, nothing – but did you see that PLANE???”…. LOL It was a fun Op.

We also ran tests from here 25 years later using an ARC Type 12 VHF AM Aircraft radio on the mountain with my buddies each using Marine Corps MAW radios on 144.450 at their respective sites. But that’s another story. See the Radio News posts elsewhere on this blog for more details on that Op.