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EM 038 B
Aperiodic suitcase receiver

EM-038-B was a binaural aperiodic receiver 1 with selective search capabilities, developed and built in the early 1960s by MTB in Boulogne (France) for the French counter intelligence service – Direction de la Sécurité du Territoire (DST). It was housed in an unobtrusive brown travel suitcase, and was used for intercepting and locating the clandestine transmitters of foreign secret agents.

The receiver covers the entire frequency range from 2 to 30 MHz, divided into six overlapping bands, each of which can be received as a whole (aperiodic) or as individual tunable narrow-band channels (selective). The desired band is selected with a large rotary knob to the left of the scale.

The device is designed for the reception of AM (A3) and CW (A1) signals, in close promimity of a suspected transmitter. Due to its dual capability, the transmitter's frequency can be determined by listening to the aperiodic receiver, whilst tuning the selective receiver to the same signal.
  
Aperiodic receiver in suitcase, with headphones

For this reason, a pair of stereo headphones is supplied, of which one side produces the sound of the aperiod receiver, whilst the other half is connected to the selective receiver. Once both sides produce the same sound, the actual frequency of the clandestine transmitter has been found.

  1. French: Valise Aperiodique (aperiodic suitcase).

Suitcase with aperiodic receiver (closed) Aperiodic receiver in suitcase, with headphones Aperiodic receiver in suitcase, with headphones Headphones (stereo) Telescopic antenna stowed in the lid of the suitcase Front panel Six band scales Adjusting the frequency
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Suitcase with aperiodic receiver (closed)
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Aperiodic receiver in suitcase, with headphones
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Aperiodic receiver in suitcase, with headphones
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Headphones (stereo)
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Telescopic antenna stowed in the lid of the suitcase
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Front panel
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Six band scales
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Adjusting the frequency

Features
All controls and connections are at the front panel of the receiver, as illustrated in the diagram below. In normal use (inside a suitacase), the control panel will be horizontal, whilst the supplied telescopic antenna is installed in the PL259 socket at the upper edge. If necessary, an external antenna can be used instead. Power is supplied by a 9V battery pack that should be connected to the 12-pin socket at the top left. The device is turned ON with the switch at the bottom right.


At the centre of the device is a rotary switch that is used to select the desired mode of operation. When searching for a clandestine transmitter, the selector is first set to APERIODIQUE to check the entire 2-30 MHz band for a station in close proximity. Next the sub-band is found by setting the selector to GAMME and check each of the six bands for the presence of the clandestine station.

When the station is found, the selector is set to SELECTIF, after which the sub-band is course-tuned to find the signal again. In this mode, the aperiodic signal is continuously heared through one half of the headphones, whilst the tuned signal is heared through the other. This is known as binaural reception. Next, the selector is set to FREQUENCE to find the exact frequency by means of zero-beat tuning. After that, the selector is set to ECOUTE for listening to the station.

Legend
  • A (Arrêt)
    OFF
  • M (Marche)
    ON
  • HP
    Loudspeaker (Haute Parleur)
  • Controle
    Check
  • Hors
    None
  • Sortie
    Output
  • Casque
    Headphones
  • Ligne
    Line
  • Attenuateur
    Attenuator
  • Quarz
    Crystal (1 MHz marker)
  • Selectif
    Selective
  • Aperiodique
    Aperiodic
  • A3
    Amplidue Modulation (AM, phone)
  • A1
    Telegraphy (CW, morse)
  • Recharge
    Search
  • Ecoute
    Listen
Meter function   controle
  • 9V
    Check input voltage (should be in the black area)
  • Hors
    None (off)
  • Sortie
    Audio output (shows VU level)
Search mode   recherche
  • Aperiodique
    Check entire 2-30 MHz band for near-field signal
  • Gamme
    Check each individual sub-band (1-2-3-4-5-6) for signal
  • Selectif
    Find station by using binaural reception (stereo)
  • Frequence
    Find eact frequency using zero-beat tuning
  • Ecoute
    Listen to the intercepted station
Operation
The following operating notes are translated from the original French instruction sheet [A]:

I. With one of the two supplied battery packs
  1. Select battery 1 or 2 — Check the voltage using the meter on the receiver with the selector CONTROLE (Check) set to 9V.
  2. Connect the headphones and install the antenna.
  3. Set the power switch to M (marche, ON) at the bottom right of the control panel.
  4. To perform an aperiodic check, set the selector RECHERCHE (search mode) to Aperiodique.
  5. To find the frequency of the intercepted transmission:

    1. Set the selector to GAMME (band).
    2. Find the band in which the transmission takes place by rotating the BAND-selector (1-2-3-4-5-6) until a tone is heared. Turn the Attenuator clockwise if the signal is too strong.
    3. Set the selector to SELECTIF (selective). The scale of the selected frequency band will be illuminated. Search for the approximate frequency of the transmission by adjusting the frequency tuning knobs.
    4. Set the selector to FREQUENCE (frequency) and find the exact frequency by means of the zero-beat tuning.

    Note: When the selector is set to SELECTIF, the aperiodic signal can be heared through one side of the headphones, whilst the other side produces the output of the selective receiver. The volume levels can be set independently at the bottom left. It is possible to demodulate both A1 (CW) and A3 (AM) signals.

II. With an external power supply unit (PSU)
  • At the top right of the battery pack, set the selector AL to AL. EXT.
  • Connect a 9V DC source to the 3-pin socket at the bottom right of the battery pack, using the supplied power cable.
For further instructions, please consult the manual [B].


Parts
Travel suitcase Receiver
RX
Headphones Telescopic antenna Rechargeable batteries Various cables Operating instructions External power supply unit
PSU
Travel suitcase
The receiver was supplied in an unobtrusive brown fibre-board travel suitcase, from within it could be operated. Inside the suit­case is a metal base plate that holds the receiver, one or two battery packs, and (optionally) a mains PSU.

The cables and any other accessories are stowed in a compartment towards the front of the case. A telescopic antenna is stowed diagonally in the lid of the case, held by two metal clips.

  
Suitcase with aperiodic receiver (closed)

Receiver
The receiver measures 380 x 265 x 220 mm and is fitted to the metal base plate at the bottom of the suit­case, by means of the large knurled bolts at the four corners, in the same way as the two battery packs are fitted.

The receiver is powered by the rearmost battery pack that is connected to the power socket at the top left. After connecting the headphones to the CASQUE socket at the left, and the telescopic antenna to the PL259 socket at the top, the receiver is ready for use.
  
EM-083B receiver

Headphones
The EM-038 comes with a special pair of head­pones, of which each side is wired separately (stereo), so that one half can be used for the aperiodic signal, whilst the other half produces the sound of the tuned signal (selective).

The headphones are connected to the receiver by means of a hard-to-find 4-pin UMD plug, of which the pinout is given below. The head­phones can only be stowed in the suitcase when the foam ear pads are (temporarily) removed.
  
Headphones (stereo)

Antenna
For operation in close proximity of a potential target, the receiver was commonly fitted with a simple telescopic antenna that was stowed in the lid of the suitcase.

The telescopic antenna was installed directly onto the PL259 socket on the front panel, and was suitable for short-range reception. If a wider range was needed, an external antenna could be fitted to the PL259 socket by means of a cable.
  
Telescopic antenna with PL259 plug

Batteries
Each EM-038 comes with two complete battery units that are installed in the left side of the suitcase, fitted to the bottom by means of two large knurled bolts. Inside each pack are two battery cells, plus a transformer that allows the cells to be recharged from the AC mains.

At the front is a selector that allows each cell to be charged individually. Furthermore, it allows an external power supply unit (PSU) to be connected to the 3-pin socket at the front. By setting the selector to EXTERNAL, the receiver can be powered directly by the external PSU.

  
Battery pack with built-in charger

Cables
The receiver was supplied with a mains power cord that should be used for charging the 9V battery packs, a special cable for the connection of an external power supply unit (PSU), and a cable for the connection of an external antenna.

When they are not in use, the cables are normally stowed in one of the two compartment at the front of the suitcase. The image on the right shows the external 9V DC power cable.
  
Cable for connection of external PSU

Operating instructions
The EM-038 was supplied with a full technical manual with circuit diagrams, plus a single sheet with brief instructions on how to operate the device, both in French. Both manuals are available for download below.

 Instruction sheet (French)
 Technical manual (French)

  
Single-page instructions

Power supply unit   wanted item
An external power supply unit (PSU) was used to power the receiver directly from the AC mains. This is done by connecting the PSU to the 3-pin socket on the active battery pack, and setting the selector to EXTERNAL.

The external PSU is not present with the EM-038 in our collection, so we are unable to show a picture of it.
  

Mains power cable Cable for connection of external PSU Cable for connection of external antenna Telescopic antenna with PL259 plug Lower end of telescopic antenna Headphones (stereo) 4-pin UMD plug Headphones stowed in the suitcase
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B
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Mains power cable
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Cable for connection of external PSU
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Cable for connection of external antenna
B
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Telescopic antenna with PL259 plug
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Lower end of telescopic antenna
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Headphones (stereo)
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4-pin UMD plug
B
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Headphones stowed in the suitcase





Interior
The receiver consists of a strong front panel and a ditto rear panel, in between which all building blocks are mounted. The interior is covered by two metal case shells that are held in place by no less than 24 screws — 6 at either surface. All metal panels are sprayed with black wrinkle paint.

After removing the 24 screws, the case shells can be taken off and the interior is exposed, as shown in the image on the right. At the top are 6 building blocks – marked BL1 thru BL6 – each of which is housed in a same-size metal enclosure.

A common axle – operated by the band selector – runs from left to right through these 6 building blocks, so that each one can select the required circuitry. In between BL4 and BL5 is the 1 MHz marker oscillator which is not housed in a metal enclosure. This oscillator is operated with the QUARZ switch at the top right of the front panel.
  
Internal units, marked BL1 to BL7

Each of the building blocks has a number of band-specific adjustments that can be reached by removing the two 'blind' panels from the front panel, and using a long (isolated) adjustment tool. In addition, BL1 (the main oscillator) has 6 adjustment which are accessible from the right side.

The bottom half of the receiver holds a large black aluminium drum in which the the band scales are engraved. Each band segment can be illuminated by a lamp that is mounted above it. The lamps can be accessed via the blind panel on the front panel, just above the scale window.

Behind the scale drum is the tuning unit, which ensures that the tuned circuits of BL1, 2, 3 and 4 are operated in tandem. The tuner is actuated by the coarse and fine tuning knobs on the front panel. Also mounted at the bottom, are the Beat Frequency Oscillator (BFO) and two AF amplifiers.
  
One of the two audio amplifiers

The BFO is housed in a metal encosure (BL7) and is operated by the potentiometer (with switch) marked A1/A3 at the front panel. The two (unshielded) audio amplifiers are mounted aside BL7 and each provide the signal for one half of the headphones. Finally, the last building block (BL8) is the adjustable attenuator, which is mounted in the upper half, close to the antenna socket.

Receiver with case shells removed Bottom right view of the interior Interior - bottom view Interior - top view Internal units, marked BL1 to BL7 One of the two audio amplifiers 1 MHz marker (calibrator) Battery cell and charge circuit
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Receiver with case shells removed
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Bottom right view of the interior
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Interior - bottom view
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Interior - top view
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Internal units, marked BL1 to BL7
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One of the two audio amplifiers
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1 MHz marker (calibrator)
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Battery cell and charge circuit

Building blocks
  • BL1
    Local Oscillator (LO) for zero-beat tuning
  • BL2
    HF amplifier with tunable band filter
  • BL3
    HF amplifier with tunable band filter
  • BL4
    Tunable bandfilter and detector
  • BL5
    Amplifier with band filter
  • BL6
    Amplifier, filter and detector
  • BL7
    Aperiodic circuit (amplifier and detector)
  • BL8
    Attenuator and high-pass filter
  • PL1
    Audio amplifier (1)
  • PL3
    Audio amplifier (2)
  • PL3
    1 MHz marker oscillator
Block diagram
The much simplified block diagram below explains how the receiver works. At the top left is the antenna input, which first passes an adjustable attenuator and a high-pass filter (BL8). From there, the signal is directly fed to an aperiodic circuit (BL7), followed by an audio amplifier (PL1). The output of PL1 is fed to one half of the headphones and (optionally) to the built-in speaker.


The antenna signal is also fed to the inputs of a band-pass filter with detector (BL5 and BL6), and to a selective direct-conversion receiver (BL2, BL3 and BL4). The audio of these last two branches is amplified in PL2 and fed to the other half of the headphones and to the line output. In order to determine the exact frequency of the intercepted transmission, the signal from an accurate Local Oscillator (BL1) can be added to the input of the selective branch, to allow zero-boat tuning. The LO can be calibrated itself, by turning on the 1 MHz marker (PL3) and adjusting 'CORRECTION'.

The Diode at the antenna input (D1) serves two purposes: it protects the HF amplifiers against strong nearby signals, and also causes harmonics to be generated when the 1 MHz marker (PL3) is enabled, so that it can be heared at 1 MHz intervals. Note that the marker can only be enabled when the MODE selector is set to FREQUENCE.


Restoration
When we acquired the EM-038B receiver featured on this page, it was in pretty good condition and did not show significant signs of use. Furthermore, the low serial number (18) suggests that only a small number of these receivers were made, probably no more than 50 or 100 units.

The most obvious problem was the wiring of the headphones. Over the years, the PVC mantle had become stiff and brittle, and around the actual earpieces, the wires were broken. Furthermore, the strain relief of the plastic 4-pin Amphenol UMD plug [3] was broken and was partly lost.

As the headphones are rather critical for the correct operation of the binaural receiver, it was decided to repair it, and replace the deteriorated PVC cable with an era-correct cloth alternative that will last for at least several more decades. The result is visible in the image on the right.
  
Headphones (stereo)

As parts of the plastic shells of the UMD plug were gone, it was decided to drill two tiny holes in the remains, and create a new strain relief with era-correct thick black waxed yarn. In order to protect the headphones against further deterioration, it is best to keep them in the suitcase when they are not in use. Note that it is best to remove the foam ear pads when storing the phones.

When the receiver was first powered on (using an external 9V DC source), it was noticed that the initial current was very high, indicating problems with some of the capacitors. The current was then limited – using a professional PSU – to avoid damage. Once the current had dropped to an acceptable level (20 - 80 mA), the receiver was first tried on a 7 MHz signal from a generator.

Everything worked exactly as described in the brief instructions, with the exception of the BFO. As the receiver can now be demonstrated, we have decided to leave the BFO-issue for now, until any technical documentation – preferably a circuit diagram – turns up.

The following items have so far been restored:

  • Padding inside suitcase refitted
  • Headphones cable replaced
  • Headphones plug partly reconstructed
  • Cracking potentiometers cleaned
Persisting problems:

  • BFO not working
  • Poor quality battery cells
Specifications
  • Power
    9V DC (from battery pack or external PSU)
  • Frequency
    2 - 30 MHz
  • Bands
    6
  • Modulation
    A1 (CW, morse), A3 (AM, phone)
  • Battery
    4 hours on single charge
  • Charge
    4 hours
Frequency bands
  1. 2.00 - 3.25 MHz
  2. 3.15 - 5.15 MHz
  3. 4.90 - 8.00 MHz
  4. 7.70 - 12.6 MHz
  5. 12.0 - 19.8 MHz
  6. 19.0 - 30.0 MHz
Components
  • RA EM038B
    Receiver (recepteur aperiodique)
  • AL EM038B
    Battery with built-in charger (alimentation)
  • ?
    Headset with 4-pin plug
  • ?
    Telescopic antenna (stowed in suitcase lid)
  • ?
    Mains power cable (2×)
  • ?
    External antenna cable
  • ?
    External power cable
  • ?
    External power supply unit
Connections
Mains power
The radio can only be powered by a 9V DC source (see below), such as the supplied battery pack. The battery pack has a built-in transformer that allows it to be recharged from the mains. The diagram below shows the pinout of the mains socket on the battery pack, when looking into it. Do not confuse it with the headphones socket on the receiver. The desired mains AC voltage can be set with the voltage selector at the bottom left of the front panel of the battery pack.

  1. 220V AC
  2. not connected
  3. not connected
  4. 220V AC
Headphones
The EM-038 comes with a pair of stereo headphones that should be connected to the 4-pin socket marked CASQUE at the left edge of the front panel. The pinout of this socket is given below. One side of the headphones is connected to the aperiodic receiver, whilst the other half can be used (simultaneously) to listen to the selective receiver.

  1. Speaker L
  2. Speaker L
  3. Speaker R
  4. Speaker R
9V power socket
The EM-038 receiver should be powered by a 9V DC source, which should be connected to the 12-pin socket at the top left of the control panel. Note that some of the pins of the (male) socket are missing, and that only two of the pins (2 and 10) are used. When looking into the socket:

  • 2
    0V (minus terminal)
  • 10
    +9V (plus terminal)
WARNING — Note that the EM-038 receiver has the (+) terminal of the battery connected to the chassis, which was common in the early 1960s. Be careful when connecting an external 9V DC power supply, as these often have the (-) terminal connected to the chassis. This could potentially cause a short-circuit of the power lines.
Documentation
  1. Instructions pour l'utilisation de la Valise Aperiodique
    Single-page operating instructions (French) [2]. 1

  2. Récepteur Aperiodique, Type EM 038 B
    Technical descriptions and circuit diagrams (French). 10 January 1963. 1
  1. Document kindly provided by Didier Clarençon [2].

References
  1. Crypto Museum, Valise Aperiodique EM-038 B
    Internal research. S/N: 18 Serie 1.

  2. Didier Clarençon, EM-038 background information
    Retrieved July 2019.

  3. UMD Amphenol, Connecteurs Rectangulaires, Série CA/CB
    Retrieved July 2019. No better copy available.
Further information
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Crypto Museum. Created: Wednesday 10 July 2019. Last changed: Wednesday, 24 July 2019 - 14:08 CET.
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