(c) 1999,2008 Peter McCollum
The RS-1 HF Transceiver
The RS-1 could be considered the 'flagship' of cold-war U.S.
clandestine radios. It's development started in 1948; and it was used by the
Agency for 12-15 years, and by the Army for several additional years. Although
smaller and lighter sets were to be developed soon after it's introduction, the
RS-1 was valued long afterward for being functional and reliable.
An RS-1 set, configured to
operate from AC mains power. Clockwise from left are: power supply, RT-3
transmitter, and RR-2B receiver. The power supply shown will also operate from
6 VDC, and has a connector for a GN-58 hand-crank generator. Author’s
collection.
Like most clandestine sets, the RS-1 has features that are
necessary or convenient for clandestine work. These features include
ruggedness; portability; waterproof cases, panels, and connectors; operation
from a variety of power sources; and operation with a variety of antennas.
Since the early transceivers were not particularly compact, it was standard
practice to make the major functional parts (transmitter, receiver, power
supply) into separate units. This allowed any one piece to be easily carried or
hidden. Compared to the technology of the day, the RS-1 is relatively large and
heavy, due to it's requirement to withstand both air-drops and burial. One of
the design challenges in the RS-1 development was to choose the correct type of
neoprene for the shaft bushings - the bushing was required to turn easily, and
yet be water-tight after long-term burial.
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RS-1 Radio Station Specifications |
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Receiver RR-2B |
Transmitter RT-3 |
Power Supply RP-1 and RP-2 |
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Weight |
10 lbs |
9 lbs |
RP-1: 24 1/2 lbs RP-2: 12 lbs |
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Dimensions |
8-5/8" X 5-1/2" X 5-7/16" |
8-5/8" X 5-1/2" X 5-7/16" |
RP-1: 10" X 8-1/2" X 5-1/2" RP-2: 8-5/8" X 5-1/2" X 5-7/16" |
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Tube complement |
1T4 RF amp |
6AC7 oscillator |
0B2 regulator |
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1L6 converter |
2E26 final |
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1T4 IF amp (two) |
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1U5 detector/audio |
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1T4 BFO/audio |
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Frequency Bands |
3-6, 6-12, 12-24 MC |
3-5.5, 6-9, 10-16, 17-22 MC |
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Power Output |
30 mW into 4K ohms |
12-15 W, 3-15 MC 10-12 W, 15-22 MC |
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The RS-1 consists of:
Receiver RR-2. Tunes 3-24 MC in 3 bands. The 1L6 pentagrid
converter tube is somewhat hard to find, and is in demand because it was used
in certain models of the Zenith Trans-Oceanic shortwave radio. It is believed
that a 1U6 would work in place of the 1L6, but 1U6's are rare, too. Tuning is
by a VFO, or an FT-243 type crystal - plugging in the crystal disables the VFO.
The receiver requires 90 volts DC and 1.5 volts DC power. The manual shows a
picture of a unit marked "RR-2", instead of "RR-2B". It is
unknown what the difference is, other than the RR-2 uses a rectangular knob for
the Gain control, rather than a round knob. The headset commonly used with the
RR-2B was the "Trimm Featherweight" model.
Transmitter RT-3. Tunes 3-22 MC, crystal controlled, accepts
crystals with 3/4" pin-spacing (i.e. FT-243), or 1" pin-spacing.
Requires 450 volts DC, and 6.3 volts AC or DC power.
Power supply RP-1 or RP-2. Input is 75-260 VAC, 40-1000 Hz; with
switch-selectable input voltage and a meter to indicate the incoming line
voltage. The RP-1 is bigger, has eight AC voltage selections, and also allows
operation from 6 VDC using a vibrator circuit. Also, the RP-1 has a connector
for a hand-crank generator type SSP-11. The SSP-11 is described in the RS-1
manual as a "modified GN-58" - the modification was likely to
permanently attach the power cable, since the RS-1 manual does not mention the
need for a separate cable. The smaller RP-2 does not support DC operation. Both
use an 0B2 as a regulator for the receiver's B+. The RR-2B receiver may also be
operated directly from a BA-48 battery. [Pictures of the GRC-109 equivalents of
the power supplies are in that section.]
The standard set also includes a maintenance kit, which includes
a few basic tools, spare tubes, fuses, antenna wire, etc. [See the picture in
the GRC-109 section.]
Each of the main units of the RS-1 set has a rubber-gasketed lid
that is attached via 4 thumbscrews, thus protecting the front panel during
transport, and when the unit was to be buried or otherwise hidden. The cases
are a single cast piece, with a screw-in dessicant cartridge.
The RT-3 and RR-2B are designed to share a common antenna,
connected via the RT-3. Users report that this hookup results in reduced
receiver sensitivity when both the receiver and transmitter are tuned to the
same frequency. However, it is likely that they were intended to be operated on
'split' frequencies, so that the enemy would have a more difficult time
intercepting both sides of the communication.
Early RS-1 units have "RDR" markings (on the knobs
and/or binding posts of RR-2B's, on the binding posts of RT-3's, and on the
meters of RP-x's). Probably RDR made the prototype and early production units,
and Admiral Corp. did the volume manufacturing (GRC-109 units, discussed in
another section, show Admiral as the contractor).
Many RT-3's have a marking on the panel that reads "MWO
39". This was apparently a Modification Work Order by the Army to add an
RF choke in the antenna circuit, from the top of C16 to ground. This choke
creates a DC path to ground for the antenna.
Some RT-3’s have also been modified to add a pair of
back-to-back germanium diodes connected between the receiver antenna connection
and ground, thus making it the same as a T-784/GRC-109 (which has the diodes in
the standard design). The unmodified RT-3 does not have the diodes, but rather
is shipped with a jumper wire installed between the "RCVR" binding
post and "GND". According to the RS-1 manual, the purpose of the
jumper is to allow the key-click filter to work correctly when the RT-3 and
RR-2 are not sharing the same antenna. The manual also mentions that
using an external key can cause high RF voltages to appear on the "RCVR"
connection, because of the loop impedance of the extra wiring. These RF
voltages can be high enough to cause damage to the receiver. So, adding the
diodes solves two problems: it eliminates the need for the jumper wire when the
RT-3 has it's own antenna; and it acts to protect the receiver when an external
key is being used.
An RR-2B receiver, part of the RS-1 set. The oblong
object in the bottom center is the crystal socket. The earliest version (RR-2)
has a rectangular-style Gain knob, instead of the round knob seen here.
Author's collection.
An RT-3 transmitter, part of the RS-1 set. All
connectors and controls are waterproof. This example is an early-production
unit, as indicated by the smaller, more-rounded key knob; and by the font used
on the panel markings. The binding posts have "RDR" markings.
Author's collection.
An example of an early RR-2B. This unit was
originally marked “RR-2”, and the letter “B” was added as a white ink stamping.
The two round knobs and the 4 binding posts have “RDR” markings. The serial
number has been mostly scratched off, but was probably 2 digits. The bandswitch
knob is round on this unit – it is possible that a previous owner swapped it
with the rectangular gain knob. Author’s collection.
RS-1 notes from a user:
Re: the headphones [for the
RS-1]. As I recall they were "Trimm Featherweights" and did fit
nicely in container and could be put away quickly. At the base we preferred the
larger types because we used to slide them up on our forehead instead of over
our ears. Of course we slid ‘em down over our ears for weak signals.
A GN-58 hand-crank
generator, commonly used to power the RS-1 in the field. Author's collection.
Some general RS-1 notes and observations
The RP-x power supply, in combination with the 'lampholder
adapter', allow the RS-1 to be operated from AC mains practically anywhere in
the world. Physically, you can plug into either US-style AC outlets, or into
round-pin (European-style) outlets. The round pins can be unscrewed and
inverted to change the diameter of the pins, plus the rubber plug is somewhat
flexible to allow changing the spacing of the pins. One part of the lampholder
adapter can be used to get power from a standard light bulb socket, or from a
bayonet-style bulb socket. [ Radio Shack sells a Euro-to-US AC plug adapter
that can be used in place of the 'lampholder adapter'. ]
The RR-2 and RT-3 are also designed with flexibility in mind.
Note that with the exception of the burst-keyer connector (not included on
standard RT-3s) and the power supply connectors, everything uses simple binding
posts for electrical connections. The author believes that this was to
facilitate emergency hookups for antennas, headphones, etc.; and these types of
connectors allow the front panel to be made water-tight more easily. For
example: One can imagine an operative in a low-priced east-Asian hotel room,
with his RS-1 set plugged into the bare bulb socket hanging from the ceiling,
the antenna wire draped across the curtain rods, and the ground wire clamped
onto the cast-iron radiator. Discovering that his headphones are missing, he
uses the TL-29 knife to cut the handset off of the telephone, strip the wires,
and connect it to his RR-2's 'Phones' binding posts. This would be a more
difficult task if the radio had something like a 1/4" phone jack to
contend with.
[See the related historical notes in the GRC-109 section.]
The introduction date of the RS-1 is about 1950, with
development work done in 1948 and 1949. As for dating any particular piece of
extant equipment, only the tubes have date codes (sometimes), but it is often
uncertain if the tubes are originals. No early-production RS-1 units have been
seen with tubes that are likely to be originals; but some late-production
RT-3's appear to have never been used, so the tubes in them are probably the
originals.
The CIA used the RS-1 extensively in S.E. Asia, Bulgaria, and
Albania; and there are documented uses of the RS-1 also in Vietnam, Tibet, and
Cuba (and probably many other places). [Ref. 27]
The U.S. Army's Special Military Intelligence Activity issued
the RS-1 to agent handlers in Vietnam, starting in about 1961. Agents used
letter drops to communicate with their handlers, and the handlers used the RS-1
to communicate with bases in Saigon, Hue, and Ban Me Thuot. Some agents also
used small commercial receivers to monitor broadcasts from their handlers. The
RS-1 was also used for training by Special Forces "Reserve" units in
1960. [Ref. 6]
Estimated dates are summarized as follows:
- RS-1:
1950-1964 (RT-3 #6487, a late-production unit, has apparently-original
tubes dated early 1964).
- GRC-109
: 1961-1969 (PP-2685 #88 has parts dated 1961).
It is noted that for RT-3 and RR-2B units, the lowest observed
serial number is 3336; and a single RP-2 has been seen with #2155. It could be
conjectured that the first 2000 to 3000 units were delivered to CIA, and
therefore never found their way into surplus channels. The higher-numbered
units (above about 3000) were perhaps the only units to go to the Army, and
thus some of them ended up in surplus.