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
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.
French: Valise Aperiodique (aperiodic suitcase).
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
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
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.
HPLoudspeaker (Haute Parleur)
QuarzCrystal (1 MHz marker)
A3Amplidue Modulation (AM, phone)
A1Telegraphy (CW, morse)
9VCheck input voltage (should be in the black area)
SortieAudio output (shows VU level)
AperiodiqueCheck entire 2-30 MHz band for near-field signal
GammeCheck each individual sub-band (1-2-3-4-5-6) for signal
SelectifFind station by using binaural reception (stereo)
FrequenceFind eact frequency using zero-beat tuning
EcouteListen to the intercepted station
I. With one of the two supplied battery packs
- Select battery 1 or 2 — Check the voltage using the meter on the
receiver with the selector CONTROLE (Check) set to 9V.
- Connect the headphones and install the antenna.
- Set the power switch to M (marche, ON) at the bottom right
of the control panel.
- To perform an aperiodic check, set the selector RECHERCHE (search mode)
- To find the frequency of the intercepted transmission:
- Set the selector to GAMME (band).
- 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.
- 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.
- 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)
For further instructions, please consult the manual [B].
- 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.
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.
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
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.
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.
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.
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.
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)
Power supply unit
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.
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.
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.
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
BL1Local Oscillator (LO) for zero-beat tuning
BL2HF amplifier with tunable band filter
BL3HF amplifier with tunable band filter
BL4Tunable bandfilter and detector
BL5Amplifier with band filter
BL6Amplifier, filter and detector
BL7Aperiodic circuit (amplifier and detector)
BL8Attenuator and high-pass filter
PL1Audio amplifier (1)
PL3Audio amplifier (2)
PL31 MHz marker oscillator
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.
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
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.
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
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
- BFO not working
- Poor quality battery cells
Power9V DC (from battery pack or external PSU)
Frequency2 - 30 MHz
ModulationA1 (CW, morse), A3 (AM, phone)
Battery4 hours on single charge
- 2.00 - 3.25 MHz
- 3.15 - 5.15 MHz
- 4.90 - 8.00 MHz
- 7.70 - 12.6 MHz
- 12.0 - 19.8 MHz
- 19.0 - 30.0 MHz
RA EM038BReceiver (recepteur aperiodique)
AL EM038BBattery 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
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
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
- 220V AC
- not connected
- not connected
- 220V AC
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.
- Speaker L
- Speaker L
- Speaker R
- Speaker R
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:
20V (minus terminal)
10+9V (plus terminal)
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.
Document kindly provided by Didier Clarençon .