(c) 1999,2008 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:
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 (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].
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 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.
A more-detailed image of the SST-1.
A more-detailed image of the SSR-1.
The SSTR-1 set mounted in a suitcase.
Transmitter panel layouts (66 KB)
Power supply panel layouts (57 KB)
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.
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.