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(c) 1999,2015 Peter McCollum

Clandestine equipment developed for the wartime OSS consists primarily of the SSTR-x series. An early unit, developed before the creation of the OSS Communications Branch, had some serious design deficiencies, and was accepted only as a stopgap until something more suitable could be developed. However, this early unit had an interesting feature: it would operate from DC (or AC) power - it had no power transformer, and used series-strung tube filaments. This early unit was replaced by the SSTR-1:

The SSTR-1 "Suitcase Radio"

Probably the most famous clandestine radio used by OSS personnel was the SSTR-1 set. It was a portable HF receiver, transmitter, and power supply combination that was typically carried in a "suitcase". RDR was involved in the development (at least for the later versions; see the "RDR Corp." section), as was Pioneer Electric and Research in Forest Park, Illinois. A manufacturer of the SSR-1 receiver is reported to have been Finch Telecommunications of Passaic, NJ [ref. 28, page 233].

The SSTR-1 set was still in fairly common use by the CIA at least through 1953 [ref 124, 125], although the RS-1 and RS-6 were delivered for new projects.

Major Henry Shore, a former RCA employee, was in charge of the development of the SSTR-1. Shore wanted RCA labs in NYC to work on the project, but they were much too busy with other wartime projects, so it was agreed that an RCA employee, Earl Anderson, would work at home on his own time. Anderson was given one of the existing AC/DC sets as a starting point, but he had to make major design changes, especially in the transmitter. According to Dean Cortright, the dimensions of the units were chosen so that they could fit inside a typical European loaf of bread. During the war, updates were made to the design, which resulted in changes in the specifications. Receivers went up to at least version "G", and transmitters to version "E". National Archives photos show at least 5 variations of the SST-1, each of which is different from the SST-1-E pictured below [see Brunner, ref. 28, pages 234-235]. One variant includes an RF ammeter to indicate antenna current, while 3 other variants appear to have a round filler panel to replace the meter with an antenna tuner knob that is marked 'RF Amperes' in conjunction with a resonance indicator lamp. The Archives photos also show two variants of the SSR-1 that are each different from the SSR-1-G pictured below. One of the SSR-1 models appears to be a very early version, as it covers 2.7-16 MC (not 17 MC), and uses a 0-100 tuning dial that is not calibrated for frequency.

SSTR-1 Radio Station Specifications

 

 

 

 

Receiver SSR-1

Transmitter SST-1

Power Supply

Weight

 5 lbs

 4 lbs

SSP-1: 10 lbs.

SSP-2: 7 lbs.

SSP-3: 23 lbs.

SSP-4: 11 lbs.

GN-35 or GN-44: 25 lbs

Dimensions

9.5" X 4" X 3"

9.5" X 4" X 3"

SSP-1: 6" X 3.5" X 9.5".

SSP-2: 4" X 3.5" X 9.5".

SSP-4: 4" X 3.5" X 9.5".

Tube complement

SSR-1-A: 6J5 RF, 6K8 osc/conv., 6SC7 IF/detector, 6SC7 audio.

SSR-1-E: 6SG7 RF, 6SA7 osc/conv., 6SG7 IF (2000 KC), 6SQ7 detector, 6SN7 BFO/audio (2000KC IF)

SSR-1-G: 7V7 RF, 7Q7 osc/conv., 7V7 IF, 7V7 BFO, 7F7 detector/audio, (455KC IF)

6L6 or 6L6G oscillator/final

SSP-1 and SSP-4: 7Z4 rectifier.

SSP-1: Mallory 642-C vibrator.

 Input power

400 VDC, 30 mA; 6.3V AC/DC, 1.5 amps

400 VDC, 75 mA; 6.3 V AC/DC, 1 amp

SSP-1-D: 90,110,125,150,200,230 VAC 40-60 cycles, or 6 VDC.

SSP-2: 6 VDC.

SSP-3: (thermo-couples).

SSP-4: 110-220 VAC, 25-60 cycles.

Frequency Bands

2.7-17 MC in 2 bands

3-14 MC in 3 bands

 

Power Output

 

8-15 watts

SSP-3: 1-2 amps for charging battery

 

The SST-1-C and earlier models had a different panel layout compared to -D and later models shown below. The -C is missing the antenna coupling indicator, has rectangular knobs, and most of the controls and indicators are located differently.

Earlier versions of the SSR-1 receiver used 6Sx7-series octal tubes; while later models used 7x7-series Loktal tubes.

The SST-1-D and SST-1-E include a rotary inductor that is described in U.S. patent 2,453,477, filed July 1944, inventor S. Irving Weiss of Radio Development & Research Corp. (see the “RDR” section). Since it is known that Earl Anderson of RCA worked on the early models, perhaps RDR was brought in to make improvements for the later versions.

The typical antenna was various types of simple wire arrangements, although the "Field Set Antenna Data" document mentions using the whip from the MAB paraset for short range (up to 15 miles).

The SSTR-1 pictured below consists of the SSR-1-G receiver, SST-1-E transmitter, and an SSP-1 power supply. Power sources could be: AC mains, or 6 VDC, or a hand-crank generator, or wood-burning thermocouples.

 

An SSTR-1 radio set. The receiver is on the left, the power supply at top, and the transmitter on the right. The key is visible on the right-most corner of the transmitter. Photo courtesy of Bill Strangfeld.

 

The SSTR-1's receiver and transmitter. Note the crystal socket (on the right), which accepts several different types of crystal holders. The receiver is marked SSR-1-G, and the transmitter is SST-1-E. Photo courtesy of Bill Strangfeld.

SSTR-1 Manual

A more-detailed image of the SST-1.

A more-detailed image of the SSR-1.

The SSTR-1 set mounted in a suitcase.

SSR-1 schematic

SST-1 schematic

SSP-1 schematic

Transmitter panel layouts

Power supply panel layouts

SST-1-B case

SST-1-B inside (1)

SST-1-B inside (2)

SST-1-B schematic

 

This picture shows an SSTR-1 set being operated from a 6V wet-cell battery, somewhere on the grounds of the OSS training base known as "Area C" (see the Training section for more info about Area C). The two men are Lt. F. Ralph Ward and John Balsamo, who was head of the Morse code section at one time.

 

SSTR-1 notes from a user:

It had a single 6L6 as a tri-tet oscillator/final and had 10 watts power output. However opening the long slender case the 6L6 was mounted horizontally and could be immersed in a jar of motor oil. Then with a better power supply I could turn this into 50 or more watts. Also with more filtering it would follow a bug at 25 wpm, which it would not do so before. There was also an ancillary unit which was a power amplifier using a single 815 tube and a pi-coupler antenna tuner in the same enclosure.

The thermocouple device [battery charger] was [nicknamed] the YTB-1 ("Yak Turd Burner"). The official nomenclature of the YTB-1 was the SSP-3.

The SSR-1 receiver was noted for drifting. We used to remove the screws from the case and remove the guts from the case just a bit, and using a pencil to move the case slightly back and forth it was nudged back to frequency.

 

The following excerpts are from an SSTR-1 instruction sheet and supplemental information:

Power Supply

The following power supplies are available. They all produce 400 v. 75 ma and 6.3 v. AC or DC at 2.5 a.

1)  P-1. Dual supply. Input 110/220 v. AC and 6 v. DC.

2)  P-2. Vibrator supply. Input 6 v. DC.

3)  P-4. Input 110/220 v. AC, 25 to 60 cycles.

4)  Hand generator. Revamped Signal Corps GN-35 and GN-44.

The P-3 is a battery charger with 1 to 2 a. output at 6 v., made of a pile of thermo-couples, and will burn wood, charcoal, gas, or kerosene. Weight 23 pounds. The low voltage side of the Signal Corps hand generators may also be used to charge 6 v. storage batteries.

Various sizes of storage batteries are supplied, the smallest of which is a 25 ampere hour type, weighing 12 pounds. This battery will operate the set for about 1-1/2 hours.

NEON LAMP AS TUNING INDICATOR

A small neon lamp which can be carried in the spare parts kit may be used to tune up the transmitter in lieu of any other means. The neon lamp should be touched against or fastened to the "antenna post". In tuning up the transmitter the lamp will glow brightest when the plate circuit is in resonance with the crystal frequency. It is NOT a good antenna load indicator since the neon lamp will glow at resonance without an antenna attached.

If the neon lamp can be attached to the far end of the antenna wire, then an indication of antenna loading will be possible. Adjust the "antenna coupling" taps until the lamp glows brightest. This method is poor security at night as the neon lamp will glow brightly in the dark.

FIELD SET ANTENNA DATA

CLOSE RANGE UP TO 15 MILES: For close range work up to 15 miles, it has been found that operating the field equipment into the antenna stick now provided with the MAB paraset equipped with a loading coil tuned to the general frequency on which the field equipment is to be operated is very satisfactory. It has the added advantage of complete mobility, since it is possible to mount this antenna on the pack board along with the field equipment.

FROM 10 TO 300 MILES: It has been found after extensive field tests that the best possible type of antenna for use over these ranges is a half wave antenna erected from 7 to 15 feet off the ground. This antenna should be either end fed, or if more convenient, fed with a single wire transmission line tapped 13% off center.



SST-103 Amplifier / Power Supply

The SST-103 is a combination power supply and RF power amplifier, in a case that holds the SST-1 transmitter. The tubes are an 815 final, plus 83 and 410 rectifiers. It operates on 110/220 VAC.

SST-103 images courtesy of Bill Adams.

 



This unidentified SSTR-1 power supply uses an internal dynamotor to operate from 12 VDC. The switch in the upper-right selects positive or negative ground. It is probably a post-war unit, and is likely intended to operate only the receiver, since the dynamotor produces only 160 V at 60 mA. Image courtesy of Tom Bryan.



This unit is believed to be a crystal calibrator for the SSR-1 receiver.

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