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Mason A-2
Portable intercept receiver

The A-2 was a technical surveillance and countermeasures (TSCM) receiver, developed in 1964 by Mason Engineering Inc as the successor to the A-1. The modular A-2 was developed by company director Frank Mason himself, and was hand-built at the factory in Fairfield (Connecticut, USA) for 16 years at a rate of one unit per week [1][3]. 1 It is capable of detecting covert listening devices (bugs) operating in the 2 kHz - 2 GHz range. 2 The Mason A-2 was used by law enforcement and intelligence agencies in the US and in Europe, including the UK, Germany and the Netherlands.
 
Visually, the A2 is one of the most interesting members of the Mason family. The unit is stored inside an unobtrusive leather suitcase, together with a range of accessories and plug-in units.

The main unit consists of a small receiver with a somewhat larger display unit bolted to its side. The various plug-in units are attached to the right side of the receiver. Each tuner is identified by a model number and in some cases a unique colour at the circular front cover of the antenna.

The display unit is basically an oscilloscope that is used as a panorama viewer, with its cathode ray tube (CRT) sticking out at the right. The CRT is slightly tilted, so that it can be viewed without tilting the receiver. On later receivers, such as the A-3B, a hinged mirror was mounted over the CRT screen, which greatly improved its usability.
  
Inside the suitcase of the Mason A-2 receiver

Over the years, the A-2 was modified and improved several times, resulting in different versions. Note that the tuners of the A-2B are not interchangeable with those supplied with the earlier A-2. Furthermore, the coloured caps on the ferrite antennas of the TLF tuners were not present on the initial version. A complete all-in-one version in an aluminium case, is available as the A-2CS.

Although the A-2 was succeeded by the A-3 in 1971, it remained in production until mid-1990. During this time, approx. 800 hand-built units 1 were made [3]. At the time of its introduction in 1964, the A-2 had a price tag of $5,000, but by 1975 this had doubled to $9,995. And ten years later, in 1985, the price had even increased to $14,950. Nevertheless, the A-2 was a very reliable product with an extremely long lifespan. The 1966 sales brochure can be downloaded below [A].
 
  1. Altough it is believed that during the 16-year lifespan of the A-2, only 800 units were built [3] at a rate of one unit per week, there are also claims that approx. 1800 units were built [2]. We believe the former (800) to be correct.
  2. The initial version of the A-2 covered 2 kHz - 1.1 GHz, but later versions of the A-2 and also the A-2B covered the full frequency range up to 2 GHz.

Leather suitcase with Mason A-2 receiver Contents of the A-2 suitcase Interior of the suitcase Close-up of the TLF tuners Panorama unit mounted to the A-2 basic unit Mason A-2 with panorama unit, LFB-1 unit and TLF-4 tuner TLF-4 tuner (70 - 295 kHz) VHF tuners

 
Controls
The diagram below provides a quick overview of the Mason A-2 receiver. The actual receiver is at the front left with the CRT unit behind it. The slightly tilted green phosphor display [6] of the CRT unit is just visible at the far right. To the right of the receiver is an adjustable IF unit and finally a pluggable tuner with its frequency scale at the front. In the image below, the 70-295 kHz tuner is mounted, which can be identified by the colour-coded (yellow) disc at the front of its antenna.


On the internal batteries, the A-2 can be used for 35 hours, or 15 hours when the display unit is in used. When using the optional external BP-3 battery pack, the A-2 can be operated for 120 hours (or 60 when the panorama display is switched on). Three power switches are important:
 
  • A-2
    ON/OFF switch
  • S-1
    Panorama Unit (display unit)
  • LFA-1
    Audio amplifier, battery pack and S-meter (not shown here)
Tuners
In order to cover the full frequency range from 2 kHz to 2 GHz, the A-2 is supplied with no less than 12 plug-in units or tuners. Each tuner covers a specific frequency range and is plugged into the right side of the main unit, in some cases via the LFB-1 unit. To get a better understanding of the concept of tuners, we will divide them into two groups: the low frequency (LF) tuners that are used for the 2 kHz to 4.5 MHz range, and the high frequency (HF) tuners (4.5 MHz - 2 GHz).
 
LF tuners   2 kHz - 4.5 MHz
Tuners TLF-1 ··· TLF-6 each have a movable built-in ferrite antenna that is mounted at the top. In addition it is possible to connect an external wire antenna or a mains antenna. When these tuners are used, the IF amplifier LFB-1 always has to be connected between the tuner and the main unit.
 
HF tuners   4.5 MHz - 2 GHz
Tuners T-18 ··· T-2000 are always connected directly to the basic unit (i.e. no LFB-1). These tuners do not have a built-in antenna and require a suitable telescopic antenna to be inserted from the right. Three different telescopic antennas are supplied to cover the entire range.

The band spread of the higher frequency tuners is remarkable to say the least. For example: the T-340 tuner covers two octaves (75 - 340 MHz), which clearly demonstrates Mason's experience as a designer of television tuners during the 1950s, before founding his own company in 1961.
 
Initial set of tuners
The following tuners were supplied with the initial version of the A-2 in 1964:
 
  • TLF-1
    2-9 kHz 1
  • TLF-2
    9-43 kHz 1
  • TLF-3
    43-130 kHz 1
  • TLF-4
    130-475 kHz 1
  • TLF-5
    475-1470 kHz 1
  • TLF-6
    1470-4500 kHz 1

  • T-5
    50 kHz - 4.5 MHz (no RF) 2
  • T-18
    4.5 - 18 MHz 2
  • T-75
    18 - 75 MHz 2
  • T-340
    75 - 340 MHz 2
  • T-900
    340 - 900 MHz 2
  • T-1100
    700 - 1200 MHz 2
  1. AC-1, LFB-1 and A-2 (or LFA-1) required.
  2. AC-1 and A-2 required.

Later set of tuners
At some point, the upper frequency limit of the A-2 was extended to 2 GHz, by replacing the upper two tuners (T-900 and T-1100) by three new ones. At the same time, The ranges for tuners TLF-1 ··· TLF-6 were changed, and tuner T-5 was dropped.
 
  • TLF-1
    2-6 kHz 1
  • TLF-2
    6-19 kHz 1
  • TLF-3
    18-70 kHz 1
  • TLF-4
    70-295 kHz 1
  • TLF-5
    295-1050 kHz 1
  • TLF-6
    1050-4500 kHz 1

  • T-5
    50 kHz - 4.5 MHz (no RF) 2
  • T-18
    4.5 - 18 MHz 2
  • T-75
    18 - 75 MHz 2
  • T-340
    75 - 340 MHz 2
  • T-650
    340 - 650 MHz 2
  • T-1200
    650 - 1200 MHz 2
  • T-2000
    1200 - 2000 MHz 2
It is not known from which serial number this change took effect, but the A-2 in our collection, with serial number 417, has the extended range. This range was also used for the A-2B.
 
  1. AC-1, LFB-1 and A-2 (or LFA-1) required.
  2. AC-1 and A-2 required.

Concealed operation
All tuners can be operated when detached from the main unit, by using one of the special cables. For the TLF tuners, a short 50 cm multi-wire cable is supplied. Note that in this mode of operation the fixation bolt has to be removed from the tuner, in order to avoid spurious noises.
 
It was possible to convert the A-2 into a body-wearable receiver, suitable for concealed or covert operation, by using an optional belt clip. In this configuration, the panorama viewer was removed from the set and the bare receiver (A-2 basic unit) was used in combination with a battery pack and one of the tuners.

For the lower frequency tuners (TLF), the IF unit (LFB-1) also had to be present, as shown in the image on the right. A 50 cm multi-wire cable, with DB-9 male/female connectors, is used to connect the selected tuner to the LFB-1 unit.
  
Body-wearable receiver for concealed use

For the higher frequency (T) tuners, a 60 cm piece of coaxial cable was supplied, which allowed the tuner to be connected directly to the A-2 basic unit.

 
Units and accessories
Leather carrying case with receiver and all accessories Basic Unit (A-2)
A-2
IF-strip, BFO and AM detector (LFB-1) Battery pack (BP-3) Mains power supply (PS-1) LF, MF and HF tuner
LF
HF, VHF and UHF tuners
HF
Panorama viewer (S-1)
S-1
Wire antenna Telescopic antenna 4.5 - 18 MHz Telescopic antenna 18 - 340 MHz Telescopic antenna > 340 MHz Mains antenna Multi-wire cable for detached use of TLF tuners Short coaxial cable for detached use of T tuners Headpones 1000 ohms

 
Suitcase
The complete A-2 receiver, with all plug-in units, accessories and documentation, came in an unobtrusive leather suitcase that measures roughly 15 x 31x 45 cm and weights ~ 5 kg.

Inside the briefcase is a pre-shaped foam interior that holds all parts. Each unit has its own tightly-fitting compartment. This way, the parts are well protected during transport and any missing units are easily spotted.
  
Leather suitcase

 
Leather suitcase Leather suitcase with Mason A-2 receiver Leather suitcase All units nicely stored in the pre-shaped foam interior Interior of the suitcase Close-up of the TLF tuners Close-up of the VHF/UHF tuners Mains PSU stored aside the receiver

 
Basic Unit   A-2
The actual receiver is marked 'A-2' and is fairly small. It contains an IF-stage, an AF-amplifier and the S-meter. All other modules connect to the A-2 which acts as the Basic Unit.

The battery pack (BP-3) or mains power supply unit (PS-2) can be attached to the left side of the A-2, whilst the LFB-1 and/or the tuners are fitted at the right side. The T-tuners can be fitted directly, whilst the TLF-tuners require the LFB-1 unit to be fitted as well.
  
A-2 Basic Unit

 
IF Unit   LFB-1
The A-2 receiver has its 1st IF frequency at 23.5 MHz. For the lower frequencies (LF), this means that the signal has to be 'up-converted' before it can be detected by the A-2 receiver.

The LFB-1 unit has to be inserted between any TLF-tuner and the A-2 Basic Unit, and contains an IF-strip, a Beat Frequency Oscillator (BFO) and an AM detector. A 'flying wire' with a black mini jack plug has to mate with the socket marked 'black' on the A-2 unit. If the panorama viewer (S-1) is used, two of its wires (black and red) should be connected to the LFB-1.
  
Control panel of the LFB-1

 
LFB-1 unit Control panel of the LFB-1 LFB-1 showing the connection to the A-2 Basic Unit LFB-1 showing the connections to the tuner Fixating the LFB-1 to the A-2 Basic Unit Complete setup without tuner Inserting an LF tuner into the LFB-1 LFB-1 and an LF tuner attached to the A-2

 
Battery pack   BP-3
For portable use, the A-2 could be powered by batteries, by using the BP-3 battery pack. The BP-3 takes 14 AA-size penlight batteries of 1.5V each, giving a total of 18.8V DC.

The BP-3 was attached to the left side of the A-2 Basic Unit. The device could be operated for 120 hours, or 60 when the panorama viewer (S-1) was installed as well. In the latter case, the S-1 unit needs two extra batteries for the filaments of the Cathode Ray Tube (CRT).
  
BP-3 battery pack

 
Mains power supply   PS-2
For stationary use, the A-2 was best used in combination with the mains power supply unit PS-2. It was installed at the left side of the A-2 Basic Unit, instead of the BP-3 battery pack.

The PS-2 is suitable for a wide range of AC mains voltages, that can be selected with a slide switch at its back. The image on the right shows a typical PS-2 unit with a US wall socket plug.
  
PS-2 mains power supply unit

Warning: be careful when connecting the PS-2 after so many years of inactivity, as its capacitors my have dried out by now, and the mains wiring may have become brittle. Connect and use the PS-2 only if you known exactly what you are doing.
 
BP-3 battery pack BP-3 battery pack (reverse side) Inside the BP-3 battery pack Close-up of the BP-3 battery pack BP-3 battery pack aside the A-2 receiver BP-3 battery pack attached to the A-2 receiver PS-2 mains power supply unit PS-2 mains power supply showing the AC voltage selector

 
Tuners
In order to cover the full frequency range from 2 kHz to 2 GHz, the A-2 is supplied with no less than 12 plug-in units or tuners. Each tuner covers a specific frequency range and is plugged into the right side of the main unit, in some cases via the LFB-1 unit. To get a better understanding of the concept of tuners, we will divide them into two groups: the low frequency (LF) tuners that are used for the 2 kHz to 4.5 MHz range, and the high frequency (HF) tuners (4.5 MHz - 2 GHz).
 
LF tuners   TLF-series
Each A-2 receiver was supplied with 6 tuners to cover the lower frequencies in the 2 kHz to 4.5 MHz range. These tuners are marked with TLF-numbers and cover the Long Wave (LW), Medium Wave (MW) and partly the Short Wave (SW) bands.

Each TLF tuner has its own ferrite antenna mounted at its top, that could be rotated for maximum or minimum signal strength. In addition, a wire antenna or a mains antenna could be connected to the side of the tuner. It was also possible to connect one of the supplied tele­scopic antennas, but with limited effect.
  
LF tuner

The exact band spread of each TLF tuner differs between the various A-2 variants, but the total frequency range was always 2 kHz to 4.5 MHz. The different sets are listed below. Note that the variants with the colour-coded ferrite antenna caps were the most common ones. Also note that when the TLF tuners are used, the LFB-1 module also has to be present. It contains the IF-strip, the BFO and the AM detector and is connected between the TLF tuner and the A-2 Basic Unit.
 
HF tuners   T-series
The higher frequencies, from 4.5 MHz to 2 GHz, are covered by another set of 6 tuners, marked with T-numbers. These tuners cover the HF, VHF, UHF and partly the SHF frequency bands.

With the initial version of the A-2, just four T-tuners were supplied to cover the 4.5 - 1100 MHz range, but the upper two tuners were later replaced by three new ones to cover an extended range up to 2 GHz. The T-tuners do not have a built-in antenna and require one of the supplied telescopic antennas to be used. The antenna is connected to two banana sockets at the right.
  
VHF tuners

Two such telescopic antennas are supplied: on for the 4.5 - 18 MHz range, and one for the 18 - 340 MHz range. Note that the three tuners for the highest frequencies (T-650, T-1200 and T-2000) have a BNC socket for connection of the antenna. A separate telescopic antenna with a BNC plug at its base is therefore supplied as well. It covers all frequencies from 340 MHz to 2 GHz.
 
TLF-4 tuner (70 - 295 kHz) LF tuner VHF tuners

 
Panorama viewer   S-1
The A-2 could be expanded with the (optional) panorama viewer (S-1). It is larger than the A-2 receiver itself, and is mounted to the back of the receiver, by means of two large bolts, so that it becomes one unit. The green phosphor screen of the Cathode Ray Tube (CRT) is slightly sloped for bettery visibility from the user's position.

The S-1 is connected to the A-2 and the LFB-1 (when used) by means of three 'flying wires' with colour-coded mini jack plugs: black, red and silver. The S-1 takes its power from the A-2, but has its own batteries for the filament of the CRT.
  
S-1 panorama viewer

 
S-1 panorama viewer Rear side of the S-1 panorama viewer Controls on the S-1 panorama viewer S-1 panorama unit placed straight up Close-up of the adjustments Close-up of the controls Fixating the S-1 panorama viewer to the A-2 basic unit Panorama unit mounted to the A-2 basic unit

 
Wire antenna
Each of the six TLF-tuners has its own ferrite antenna mounted at the top. In addition it is possible to connect a wire antenna directly to the banana socket at the right side of the tuner.

A suitable piece of wire with a banana plug at one end, wound onto a piece of carton, is supplied with the set.
  
Wire antenna

 
Telescopic antenna   4.5 - 18 MHz
For Short Wave (SW) frequencies between 4.5 and 18 MHz, a suitable telescopic antenna is supplied with the set. It can be inserted into the right side of a T-18 tuner by means of two fixed banana plugs. Note that this antenna is not suitable for any of the other tuners.

At the bottom of the antenna is a small switch for selection of the required sub-band: eiter 4.5 - 10 MHz or 10 - 18 MHz.
  
Telescopic antenna for 4.5 - 18 MHz

 
Telescopic antenna   18 - 340 MHz
A similar telescopic antenna is supplied for the VHF/UHF 18 - 340 MHz range. It is nearly identical to the antenna show above, but does not have the sub-band selector.

This antenna is suitable for the T-75 and T-340 tuners only. It can be used in combination with the TLF-tuners, but with limited effect.
  
Telescopic antenna for 18 - 340 MHz

 
Telescopic antenna   > 340 MHz
The three tuners for the upper frequency ranges (T-650, T-1200 and T-2000) are not equipped with banana sockets. Instead, they have a BNC socket for connection of the antenna shown in the image on the right, or an external antenna.

The antenna shown here is supplied with the set and is suitable for all frequencies between 340 MHz and 2 GHz. As a general rule of thumb, the lower the frequency, the further the antenna should be extended.
  
Telescopic antenna with BNC connector

 
Mains antenna
In addition to the antennas shown above, it was also possible to use the wiring of the mains AC power network as an antenna. A suitable mains plug/wire combination is supplied with the set.

This type of antenna is suitable for use in combination with the TLF-tuners only. The banana plug should be connected to the lower banana socket of the tuner.
  
Mains antenna

 
Wire antenna Telescopic antenna for 4.5 - 18 MHz Frequency range selector on the antenna Selecting the appropriate frequency range Telescopic antenna for 18 - 340 MHz Antenna connected to a T-tuner Telescopic antenna with BNC connector Mains antenna

 
Multi-wire cable for detached use
When using the TLF-tuners in a detached configuration, this 50 cm piece of multi-wire cable should be used to connect the TLF-tuner to the LFB-1 unit.

It allows the tuner to be held (and tuned) in the operator's hand, whilst the receiver is attached to the operator's belt. For concealed use, a special belt clip was available.
  
Cable for detached use of the TLF tuners

 
Coaxial cable for detached use
The six tuners for the higher frequencies (T) can also be used in a detached configuration, by using the 60 cm coaxial cable shown in the image on the right. It connects the T-tuner directly to the A-2 Basic Unit.

It allows the tuner to be held (and tuned) in the operator's hand, whilst the receiver is attached to the operator's belt. For concealed use, a special belt clip was available.
  
Coaxial cable for detached use of HF (T) tuners

 
Headphones
The A-2 receiver delivers its demodulated audio (AF) to a pair of 1000 Ohms headphones.

As the original headphones are currently missing from the A-2 set featured on this page, we are not able to show them.
  

 
Modules
  • Basic Unit (without tuner)
  • LFA-1
    AF Amplifier, internal batteries and S-meter
  • IF strip (455 kHz), BFO, AM detector
  • Tuners for the 2 kHz - 4.5 MHz range (see below)
  • Tuners for the 4.5 MHz - 2 GHz range (see below)
  • Accessories: case, antennas, wiring, headphones, tools, etc.
  • Panorama Unit (display)
  • External battery pack (optional) for 120 hour use
  • Mains power supply (95-250V AC in, 18V DC out)
Batteries
  • A-2
    Basic Unit: 2 x Mallory TR137R @ 9.8V
  • BP-3
    Battery Pack: 14 x Mallory RM12R @ 1.35V (18.8V)
  • S-1
    Panorama Unit: 2 x Mallory RM12R @ 1.35V (parallel)
  • LFA
    Audio Amplifier S-Meter: 5 x Mallory TR133R @ 4.05V
Technical specifications
  • Frequency
    2 kHz - 1200 MHz (2000 MHz on the later version)
  • Sensitivity
    Better than 3µV for 10dB of (S+N)/N
  • Modulation
    AM, FM, CW (other signals detected b
  • Gain
    Sufficient to read-out thermal noise
  • Audio
    300 - 3000 Hz
  • Panorama
    3% of center frequency
  • Power
    1.5W (with all circuits on)
A-2 main unit
  • Functions
    IF amplifiers, detectors, AF amplifier, S-meter, BFO, power
  • Dimensions
    143 x 102 x 46 mm
  • Weight
    3 lbs 136 grams
  • IF frquency
    23.5 MHz
  • IF bandwidth
    12 kHz, 90 kHz, 200 kHz (other bandwidths on special order)
  • Audio
    30 mW into 1000 Ω
  • Inputs
    IF (50 Ω @ 23.5 MHz), external power
  • Outputs
    Audio, -18V DC, second detector, -12V DC regulated
Bandwidth
  • Nar
    12 kHz (narrow)
  • Med
    100 kHz (medium)
  • Wide
    350 kHz
Versions
  • A-2
    Initial version (up to serial number 621)
  • A-2B
    Serial number 621 and higher 1
  • A-2C
    With subcarrier option (only 64 ever made)
  • A-2C-S
    All in one unit
  1. Electrically and operationally, the A2-B is identical to the A-2. The only differences are the use of different connectors on the tuning units and the use of different transistors in some circuits. As a result, the modules of the A-2B are not interchangeable with those supplied with the earlier A-2.

Documentation
  1. F. G. Mason Engineering Inc., A2 Brochure
    1 January 1966.

  2. PTT, Funküberwachung, Mason A-2, Kurzbeschreibung
    Short description for the user (German). Switzerland. 13 December 1974. 1

  3. F.G. Mason Engineering Inc., Mason A2 drawings and controls
    January 1971. 2

  4. F.G. Mason Engineering Inc., Radio Receiver with spectrum display, Model A-2B
    Technical Manual. December 1976. First released February 1970.
    Gift from The Military Collection Gausdal 2

  1. Manual kindly supplied by Immo Hahn [4].
  2. Manual kindly supplied as a gift by The Military Collection Gausdal [5]. This site also contains extensive information and pictures of related equipment. More...

References
  1. Personal correspondence with a former Mason employee
    Crypto Museum. January 2009.

  2. Granite Island Group, Used equipment price index list
    Retrieved January 2009.

  3. Kevin D. Murray, Mason Enigineering Model A-2CS, etc.
    Forum discussion on spybusters.com. 16 Jan 2005.

  4. Immo Hahn, A-2 Short German user manual - THANKS !
    Created by the Swiss PTT. See above under [B]. 10 May 2012.

  5. The Military Collection Gausdal, A-2B Technical Manual - THANKS !
    See above under [D]. Received 15 January 2015.

  6. Wikipedia, Phosphor
    Retrieved May 2012.

Further information

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Crypto Museum. Created: Thursday 29 October 2009. Last changed: Friday, 21 October 2016 - 14:59 CET.
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