(c) 2000,2018 Peter McCollum
The TAR-224 Transceiver
The TAR-224 is a complete radio transceiver. Although it is housed in a single case, the major components are described as the RT-224 transmitter, the RR-224 receiver, a TYPE-224 battery, and the crystal selector CS-224. The manual for it is dated 1 July 1970, and was updated 15 September 1971. The set was produced by AVCO Corporation, Electronics Division, in Cincinnati, Ohio. Since the “TAR-xxx” nomenclature does not match the known CIA standards, and the manufacturer’s ID plate is on the sets, it is possible that “TAR-224” is an AVCO designation.
The set is mentioned in a CIA memo from March 1973, where a commo officer travelled with a TAR-224 set and one-time pads. Another memo mentions that 392 sets were being tested in February 1975, and there is mention of needing to identify a repair source for those that failed. By August, a contractor was on duty to work on the repairs. The set appears on a list of equipment used in Angola in 1975, and a former user reports using a TAR-224 in the field (in Europe) as late as 1981. An October 1976 memo mentions that KE/M-8 [keyers, a modified version of KE/G-8] were about to be shipped with TAR-224 sets.
The time of the TAR-224, the 1970's, represents the beginning of a transitional period for U.S. Clandestine radios. Custom-designed agent radios for long-range communications are being replaced by more commercial-oriented devices and communication networks. CW and Morse code is about to be replaced by complex digital modulation schemes. There is less interest in hiding the source of the equipment, as seen in this case by the manufacturer's name being included on the ID plate.
This set shows some influence from the military community in the design. The audio connectors mate with U-229 plugs, making them compatible with various military phones and mics, such as the H-251A/U headset. The power connector is a MIL-standard type. These connector choices do not allow “field expedient” hookups, as most of the earlier sets did. The inclusion of the AM transmitter mode may also be a military influence. Clandestine users would only require CW, particularly in combination with a burst keyer. A cable-type connector that mates with the 3-pin male POWER connector is the Amphenol PT06A-8-3S. This type of connector is still being made, and sold through electronics distributors.
The TAR-224 set includes a motor-driven auto-tune system for the transmitter antenna matching. Gabriele (IK6QNE) reports that the system does not work well with a tuned HAM antenna. His theory is that the auto-tune is not suitable for a high-Q antenna – it cannot react fast enough during the scan process, so it fails to stop on the “peak”. The system may be intended only for simpler antenna systems, such as a long wire.
There is also a “TAR-224A” set, but the differences are unknown.
A predecessor to the TAR-224 appears to be the RS-101 – see the “Other CIA Sets” section.
Norris D. reports the following interesting information, and provided the 4 documents linked below:
I had the dubious fortune to work on scores of [TAR-224] when I worked for WES Industries in Dumfries, VA in 1971-1972. Evidently, AVCO had run out of resources when the time came to ship, with the result that the TAR-224 units were shipped without final testing; and as a consequence most of them didn’t work. WES Industries must have been the low bidder to put them in working order; we were frequently the low bidder on security projects of this kind. I was one of two techs tasked with bringing them to operational condition. [The other tech] and I disassembled each of the units, made modifications to improve/attain reliability, fixed the known problems, troubleshot where necessary, and ran burn-in tests before returning them to the customer.
The most frequent reliability issues related to solder connections to the ground plane on the back of the receiver PC boards. Although plated-through holes were a known technology at the time, AVCO made the through-board connections with eyelets. I don’t know what those eyelets were made of, but they wouldn’t take solder. We often resorted to soldering a short length of wire through the holes to pads on each side of the board.
I used to keep a big, black shingling hatchet on the wall above my bench, engraved with “TAR-224 Final Test.” I have that hatchet to this day.
Many thanks to Norris for these interesting historical documents:
The TAR-224 transceiver. Author's collection.
A TAR-224 transceiver with the CS-224 crystal selector installed. The plastic lid is visible in the background.
The AC power supply for the TAR-224 set, model W12-6, made by RO Industries. Note that the designation and manufacturer is marked on the set, and it is not a military designation. Image courtesy of Gabriele IK6QNE.
A view of the ID plate. Note that it names the manufacturer.
It is unknown what was changed for MWO 170-1.
This view shows auto-tune motor, the antenna-matching variable inductor (left), and the tuning capacitor (rear center).
The ball-chain is part of the bandswitch mechanism.
The following 3 pictures are believed to be of a prototype frequency synthesizer for the TAR-224 set. The synthesizer is mentioned in the manual, but no details are given. The unit shown here was constructed using the case and panel of a CS-224 crystal selector. It was clearly professionally made, and the smaller chips have date codes from late 1982. Gabriele IK6QNE reports that the synthesizer is functional, however it outputs a signal at all times, even when the transmitter is not active, so it causes a beat frequency in the receiver. Images courtesy of Gabriele IK6QNE.