(c) 2000,2008 Peter McCollum
Surveillance and Bugging Devices
While one part of the Agency handled the traditional communications role, including the design, construction, and use of radio equipment; there was a separate group known as the Technical Services Division (TSD), which was responsible for providing a wide range of devices to operatives; including equipment for audio surveillance, clandestine photography, and lock bypass. Later, the equivalent of TSD became the Office of Technical Service (OTS).
For more information about TSD, OTS, and the technical devices, projects, and operations, see the book “Spycraft” ( click here ).
The SRR-4 Surveillance Receiver
This receiver is for general-purpose surveillance work. Based on tube date codes, it was likely made in 1961 or 1962. It receives FM, AM, and CW signals in a single band from 50 to 200 MC, with calibration points every 5 MC. The design includes 13 subminiature tubes, plus several germanium diodes, and 3 transistors (in the power supply module).
The SRR-4 would be ideal for monitoring “bug” transmitters, such as the ST-2A (described in the next sub-section). The set is featured in H. Keith Melton’s book “CIA Special Weapons & Equipment” on page 52.
The SRR-4 receiver, serial # A59. The whip antenna can
be mounted as shown, or perpendicular to the front panel when the receiver is positioned
face-up. The antenna extends to a length of 53 inches. Since the set has a BNC
connector for the main audio output, an included accessory is an adaptor to
allow a 1/4-inch phone jack to be used with standard headphones. The power cord
shown is for 220 VAC operation. This particular unit was part of a
“stay-behind” program in
The 10-pin power input connector mates with a U-77 plug,
the same as the audio connector on many 1950’s-vintage military sets. The
DETector AUDIO output is suitable for connection to a recorder (wire or tape).
The
Inside the rear of the case is a “PP-1A/ASR” power supply (the module in the middle), and battery compartments on either side. The batteries (1.5V and 45V) are accessed from panels on each end of the case.
The circuitry includes 9 plug-in modules (the gray
objects with colored arrows), plus 4 additional subminiature tubes. The plug-in
modules perform functions such as IF amps,
An upper view of the chassis. Note the 1N21B cartridge-type diode, under the screwdriver cap at bottom-center.
Inside the PP-1A/ASR power supply. Note the two unusual dome-shaped power transistors used in the DC-DC converter. Directly below the transistors is a toroidal inverter transformer, and another early germanium transistor. Two of the original electrolytic capacitors have been replaced with newer Japanese-made units.
The ST-2A Surveillance Transmitter
[Thanks to Jim Mahaffey for finding an example of this equipment.]
The ST-2A is one of the earlier models in a long series of equipment. The purpose of a surveillance transmitter (ST) is to transmit the sounds (conversations) from within a room to a person or recording device monitoring a receiver nearby. For example, an ST may be hidden in a hotel room before the targeted person arrives, and the opposition can set up equipment on an adjacent floor to monitor and record any conversations that take place.
The ST-2A as shown in the manual.
A view of an ST-2A with the cover removed. One of the 1AD4 tubes is visible on the far right. The two gold connectors are for RF out and audio in. On the bottom right corner is an access panel for tuning. The AC power cord comes in from the left. Author's collection.
This model is a hybrid design, using two 1AD4 tubes and 3 type 2N207B transistors. The three transistors are a basic audio amplifier, one tube is the RF oscillator, and the second tube functions as a doubler. The unit operates from 115 or 230 VAC, 50-60 cps, unswitched. The output frequency is in the range of 56 to 84 mc, FM, and produces at least 30 mW of RF power into a 50 ohm load. It measures 5-5/8" X 3" X 1-1/4", and weighs 19 oz. The suggested microphone is a Shure MC-11 (1K ohm dynamic, 400-4000 Hz), and the antenna is a 40" length of Amphenol No. 14-500 cable (Amphenol lists this as a "Sub-Minax" cable). The mic input connector is a type SMC, and the RF out is an Amphenol "Sub-Minax" connector.
Referencing the picture above, the major components in the unit, from left to right, are: power transformer, low-voltage rectifiers and filters board, high-voltage rectifiers and filters board, audio board (3 transistors plus a deviation adjustment pot), and RF board.
The only controls or adjustments are an oscillator tuning coil, a doubler tuning coil, and an audio FM deviation control pot. There is an access panel that allows adjustment of the tuning while the cover is in place.
The overall tuning range for the ST-2A is 56 to 84 mc, but each individual unit was pre-tuned at the factory to operate on one of three frequencies: 59 mc, 68 mc, or 77 mc. Each unit has a colored marking on the corner of the case to indicate which of the factory tunings has been applied; the colors are green, blue, and white respectively. According to the manual, each unit can be re-tuned by the user over an 8 mc range, which implies that there are some component differences between the green, blue, and white units.
The power supply provides 2.5 VDC for the tube filaments (1.25 V each, in series); 65 VDC for the tube plates; and 5 VDC for the transistors. Rectifiers are germanium 1N91 and 1N93 types.
The ST-2A was used in about 1956 and 1957 (3 extant units have 1957 date codes on some components). There were reliability problems with the 1AD4 tubes - they would often lose filament emission after 50-100 hours of operation. The ST-2A was replaced by the 'Surveillance Radio Transmitter' SRT-3, which was all solid-state, and about 1/3 the size. At that time the nomenclature changed from ST-x to SRT-x. The SRT-1 and SRT-2 were prototype models that were never generally used. The SRT-3 was a well-used item for a number of years, and was eventually followed by a long series of SRT-x units, up to about SRT-44.
DD-4 Microphone
[Thanks to Jim Mahaffey for finding an example of this equipment.]
This mic measures 1-5/8" in diameter and is 7/8" thick. It is a dynamic type, and seems to contain a fairly large magnet. It may be intended for use with the ST-2A, since its features are roughly similar to the Shure MC-11 recommended in the manual.
The type DD-4 microphone. Author's collection.
Induction Coil (Wire Tapping Device)
[Thanks to Jim Mahaffey for finding an example of this equipment.]
This device, marked “F-371 IndCoil”, is an audio wire tap, most likely intended for telephone lines. It is an inductive pickup, so does not require any direct connection to the signal wire. This makes it much more difficult to detect, and does not interfere with telephone operation in any way.
When clipped over the red wire on a traditional telephone line, and connected to a suitable preamp, it can efficiently monitor a conversation. Note that it is necessary to tap only one of the two signal wires – if both wires pass through the device, the signal is cancelled. The tap includes a square, closed armature that is opened by pushing a spring-loaded button. Two sides of the square have fine wire coils wound on them, connected in series.
Although this item formerly belonged to a TSD employee, veterans of TSD that were contacted do not recognize this particular model as a ‘stock’ item. It may be a sample or prototype.
The wire-tapping device. Pushing the black button on the right side causes the armature to open so that it can be clipped over a wire. The oblong aluminum portion is a separate impedance matching transformer, marked “3.2” (ohms) on the input, and “1200” on the output. It has a 1/8” plug on the input side, and a matching jack on the output side. Author’s collection.
Unidentified Subminiature Audio Amp
[Thanks to Jim Mahaffey for finding an example of this equipment.]
The exact purpose of this device is unknown, however
it is extremely similar to an early transistor hearing aid, but without a
built-in microphone. It is a small aluminum clamshell box, about 2.5"
long, containing a 3-transistor audio amplifier. It uses early Raytheon
germanium transistors (one is a CK721 with a mid-1953 date code), and the
stages are transformer-coupled. The required battery is about the size of an
'N' cell - there is a hand-written note inside the case lid saying that the
battery is 2.6 volts. The output connector is a 2-pin hearing aid earphone
connector. The input is a tiny 7-pin
Three views of the submini amplifier. The black component in the lower left, marked "3-21", is one of the 3 transistors. The color-coded resistors are 1/2 watt units (for size comparison). Author's collection.
Japanese-made Audio Amplifier
[Thanks to Jim Mahaffey for finding an example of this equipment.]
This device is another simple audio amplifier, but in
this case it was made in
The inside of the lid and the inside of the box each are stamped "1". Since before WWII, Japanese manufacturing was in the habit of marking pieces with an 'assembly number', since many pieces were hand-fitted to each other. So, it is possible that this unit is a prototype.
The "Japanese amplifier", with the cover removed. The two gray objects are the Sony transistors. The input connector is on the right (not visible), and the output is on the left. The red and blue leads on the left are the power input. The white, blue and brown wires connect to the output connector, but are not attached on the other end. Author's collection.
Maico Hearing Aid
[Thanks to Jim Mahaffey for finding an example of this equipment.]
Maico is a commercial hearing aid brand that dates from the late 30's. The "Transist-ear" is one of their earliest solid-state models, using three CK718 transistors.
This one has had its mic removed, and a 1/8" phone jack added in its place. It was obviously being used as a subminiature mic preamp, similar to the custom-made unit described above.
Front and back views of the modified Maico hearing aid. The added 1/8" phone jack is visible at the top. Author's collection.
Unidentified
[Thanks to Jim Mahaffey for finding an example of this equipment.]
This unidentified battery box was machined from translucent black plastic, with phenolic inserts mounted from behind with small screws. It appears to accept two 30 volt batteries, and six 'N' cells. The box measures 5-5/8" X 2-1/2" X 7/8".
Assuming that the two large batteries are 30V each, and that each small cell is 1.5V; then the box could provide any of the following outputs: +60V (with or without 300 ohm resistor in series), +30V, -1.5V (two cells in parallel), -6V, and -3V.
The battery box with the cover removed. In the center is a pair of contacts that are normally shorted, but when a plug is inserted through a hole in the case, the contacts open and are shunted by 300 ohms. Author's collection.
Centralab "Ampec" Amplifier Module
[Thanks to Jim Mahaffey for finding an example of this equipment.]
The "Ampec" is a commercial audio amplifier module from circa 1952. It was found in the same lot of equipment as the ST-2A, the submini amp, and the battery box described above. TSD may have considered using it as a building block for some device.
It is a 3-stage R-C coupled audio amplifier, using submini tubes and a 1-piece substrate for the other components. The instruction book suggests how to use it as a simple radio, a hearing aid, a phono preamp, etc.
The "Ampec" module and its instruction book. Author's collection.
Home-made Surveillance Devices
Shown here are some devices constructed by the author, as an exercise in building various surveillance devices using 50's or 60's vintage components wherever possible.
This is a “bug” transmitter, built as a working copy of the “book-spine transmitter” shown in Keith Melton’s “Ultimate Spy” book (page 103 of the newer edition, page 83 in the older edition). From the bottom upward, the major components are: mic element, 1st audio stage, 2nd audio stage, RF oscillator, and 3 batteries. The transistors are 2N591 (two, audio) and 2N499. The antenna is a PC trace that goes around the perimeter of the board, thus forming a loop. This loop is also the “L” in the RF tank circuit. The “C” in the tank is the distributed capacitance of the components. The frequency is in the 80 MC range, making it similar to the ST-2A described above. RF power is estimated to be 3 to 4 mW.
Schematic of the “book-spine transmitter” (41 KB)
Shown here is another home-made surveillance transmitter, with features that include: AC power (like the ST-2A), tunable from about 70 to 90 MC FM, all solid-state with early 1960’s transistors, and a built-in microphone. The mic is a tiny hearing-aid element in the top center, glued to the brass tube which provides a coupling to a length of translucent plastic tubing. The antenna connector is a pin jack, seen on the right. The three transistors just to the right of the transformer are the audio stages; while the two near the antenna jack are the RF oscillator and buffer stages.
Schematic of the home-made transmitter (131 KB)
A general-purpose 3-transistor audio amplifier, assembled in a small tin box. On the right is a gain control and a power switch. At the bottom are the input and output jacks.
The schematic of the amplifier. Note that the input provides a source of DC power, which can be used to operate transducers that contain an active preamp. The use of germanium transistors allows the design to be simple, and to work effectively from a single 1.5 volt cell. The 0.01 uF cap at the input is to shunt any RF signals to ground, which is necessary when the amplifier is used to drive a transmitter.
A tiny hearing aid microphone is hidden inside this vintage fountain pen cap, along with a 1-transistor preamp. The small hole near the top is the sound inlet.
The schematic of the fountain pen microphone. It's DC power is drawn from the output connection. As with the amplifier above, there is an RF bypass cap included.
This unit is an AM transmitter assembled in a small tin box. It is designed to connect to the audio amplifier above. On the right, the power switch and antenna wire can be seen. The transmitter is tunable from 1500 to 2000 KC.
The schematic of the AM transmitter. Although it works as designed, it is effective only with a long antenna wire, or a very sensitive receiver. Note the two 3.3K resistors - if one is jumpered, then the power output is reduced. The 2N43 directly modulates the RF oscillator, so there is likely some FM component introduced as well.