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(c) 1999,2015 Peter McCollum

Other WWII OSS Equipment 


The SSTR-4 Radio Set

The SSTR-4 is a relatively large, semi-portable HF transceiver developed by RDR (see the "RDR Corp." section) in late 1943. It includes the SSR-4 receiver, SST-4 transmitter, and SSP-4 power supply.

The SSR-4 receiver tunes 2-18 MC in two bands with a standard 455 KC IF. One interesting design feature is that the bandswitch appears to be made of 3 bat-handle toggle switches that are mechanically ganged together under the chassis.

The SST-4 transmitter is CW-only, tunes 2.4-16 MC with a crystal or VFO, and has a 100 watt output.

The SSP-4 power supply unit accepts 105/115/125 VAC 60 CPS input at 400 watts, and provides voltages of 1350, 350, 250, 150, 10, and 6.3. The SSTR-4 set also includes a 400 watt gasoline powered generator.

SSTR-4 Radio Station Specifications





Receiver SSR-4

Transmitter SST-4

Power Supply SSP-4









Tube complement

6S7 RF amp

802 oscillator

866A rectifiers (two)


6K8 mixer

802 driver

83 rectifier


6F7 IF amp/BFO

813 final

VR-150 regulator


6SQ7 detector/ AVC/audio




6C5 audio




VR-105 regulator



Frequency Bands

2-6.2, 6-18 MC

2.4-16 MC


Power Output


about 100 watts



A rear view of the SSR-4 receiver, from the manual. No front views are available.

SSR-4 schematic

SST-4 schematic

SSP-4 schematic


The SSTR-5 Radio Set

This set was apparently developed late in the war, was considerably smaller than the SSTR-1, and was carried in a canvas shoulder bag. Components include the SSR-5 receiver and the SST-5 transmitter. The set is designed to be operated from battery power (the receiver uses 135V, 6V, and 1.5V). In addition to the standard model, both "A" and "B" variants were made. The SSR-5A receiver was made by Philharmonic Radio Company of NY [ref. 28, page 233].

SSTR-5 Radio Station Specifications




Receiver SSR-5

Transmitter SST-5


2.75 lbs



7.5" X 3.5" X 4.625"


Tube complement

1T4 RF amp

3S4 osc. (two)


1R5 converter



1T4 IF amp



1S5 detector/audio



1L4 audio





Frequency Bands

2.5-12 MC in 2 bands


Power Output


about 0.5 watts


An SSTR-5 set. Image courtesy of Joe N2GBT.

Another SSTR-5 radio set, with an SSR-5-A receiver. Photo courtesy of Bill Howard.

An SSR-5-B receiver. Image courtesy of Joe N2GBT.

The SSTR-5 transmitter. Photo courtesy of Bill Howard.

The tuning instructions for the SST-5. Image courtesy of Joe N2GBT.

SSR-5 schematic


The SSR-201 Aperiodic Receiver

The SSR-201 is a very wide-band receiver whose output operates relay contacts, presumably to enable a warning device for someone nearby. The circuit has no RF or IF stages – a 1G4 diode detects an RF signal directly.

Tube complement: 1G4 detector, 6SQ7 amp, 6J5 amp, 6C6 push-pull amp (two), 6SL7 DC amp, 6SL7 tone generator, 6V6 audio, 6G5 indicator, VR105 voltage regulator (two).

A front and top view of the SSR-201 aperiodic receiver. This set is on
display at the Dutch Amateur Radio Museum 'Jan Corver'. Images courtesy of Louis Meulstee.

Comments from a user:

Regarding "aperiodic" when applied to radio receivers, it means that the receiver is fix-tuned and designed to have very broad response to incoming signals.  I suspect this one covered the HF signals ordinarily used by clandestine stations. It is designed for "stalking" radio signals by RDF stations and others who are trying to locate the station and put it out of business. A station who has reason to believe that he is being stalked will change frequency often to make it harder for the DF station to get a "fix" on it.  The aperiodic receiver is so broadly tuned that even when the station changes frequency, he will still be within the range of the aperiodic receiver without having to be retuned. A receiver so broadly tuned is not very sensitive and requires that the signal being pursued be quite strong... at least stronger than others who are transmitting at the same time.


SSP-12 Gas Generator

This gas generator is assumed to be another item produced for OSS use, based on the nomenclature. It is a 2-stroke gas generator that produces 115 volts 400 Hz single-phase AC power. Markings say “BANTAMAG, Wilco Electronic Co., Springfield Mass.” The manual (“POWER UNIT SSP-12 Operating Instructions”) is dated February 15th 1945. The manual does not mention use with any radio equipment, but does mention that it complies with Signal Corps Spec. No. 72-0-1. The spare parts kit includes 3 open-end wrenches, a spark plug wrench, Allen wrench, screwdriver, and various parts. The overall functionality appears to be similar to the UGP-12 generator used with the later GRC-109 set. The following images are courtesy of Len Krapcha.

Other OSS Projects

Following is a list of OSS radio systems, and the cost paid by the government for some of them. The costs are apparently available on a National Archives document:

Much info about OSS equipment in general can be found in Dr. John Brunner's book; see .


NDRC Projects

During the war, OSS initiated several projects that were handled separately from the 'main-stream' agent radio designs. OSS provided the requirements, and Division 13 of the National Defense Research Committee (NDRC) worked with contractors to implement the ideas.

In 1942, OSS indicated a requirement for a small radio receiver which, when it received the correct signal, would detonate an explosive. One plan, which was never implemented, was to secretly place many of the receivers around occupied Europe, and they would all be detonated simultaneously by large Allied transmitters. For this plan, the receiver would respond to a signal at 113 KC from a distance of at least 500 miles. Known as the Mitchell Device, it was a 6X9X4-inch metal box, and included a plastic-explosive booby trap so that it could not be disturbed once it was armed.

Another version was to be triggered by an overhead aircraft transmitter using a signal at about 90 MC. Known as the VanVoorhis Device, agents would place the receivers at future bombing targets. The intention was that bombers could "light up" their targets as they approached at night. This project was supervised by Division 13, and the contractor was Galvin Manufacturing Co. with assistance from Bell Telephone Laboratories. The Signal Corps had been kept informed of the project, and they assigned a nomenclature of "Radio Receiver R-37 ()CR". An early version was based on radio-controlled model airplane circuits, and used a QF-6 gas-filled triode as the detector. The QF-6 was found to be unsatisfactory at 90 MC, so the unit was redesigned to use a 957 super-regenerative detector, and a 1S5 audio detector and amplifier. After successful testing in April 1944, the OSS placed an order for 1000 units with the Howard Radio Company in Chicago.

A third version was developed, which was intended to be triggered by a ground-based HF transmitter operating in the 3-8 MC range. It was a 5-tube superhet design, and designated "SSR-204".

Another pair of devices, known as an IFL and IFT B-12, were developed as very short-range (up to 125 yards) signaling devices. The IFL was a beacon transmitter operating from 40 to 60 KC through a small loop antenna; and the IFT was a transceiver on the same frequency. The IFL was attached to air-dropped packages, and the IFT was used by personnel in the same drop to locate the supplies, and each other.

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