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Autophon SE-20
Secure handheld radio

The SE-20 is a half-duplex handheld radio, developed by Autophon (later: Ascom) in Solothurn (Switzerland) around 1981. The device operates in the VHF-L, VHF-H or UHF band and can be expanded (optionally) with a voice encryption unit that can be mounted at the radio's rear side.

Depending on customer requirements and the radio's application, the SE-20 was available in a variety of colours, including signal orange and dark green, as shown in the image on the right.

In this case, the actual body of the radio is dark green and has a fairly large battery connected at the bottom end. The (black) encryption unit 1 is mounted at the rear and makes the radio about twice as thick as a standard one. The radio was normally carried in a suitable leather carrying case. The price of a single SE-20 radio (without encryption) was around EUR 1500 in 1989 [2].
Autophon SE-20

The SE-20 was introduced in 1981 and was sold under the Autophon brand name, even after the company was merged with Zellweger and Hasler into ASCOM in 1987. Rather than featuring real digital speech encryption, the SE-20 was fitted with an early implementation of a time-division speech scrambler, made by BBC. Nevertheless, it was the start of a successful line of handheld radios like the SE-110, SE-120 and SE-140. The last portable radio in this range, which featured real digital speech encryption, was the Ascom SE-160. It was sold under many brand names.

  1. Although the speech scrambler used in the SE-20C is not truly an encryption unit, we will use that terminology on this page, as that is what the manufacturer called it at the time.

Autophon SE-20 Autophon SE-20 Control panel Controls SE-20 with battery removed Autophon SE20 in leather case with carrying strap The SE-20 and the SE-160C
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Autophon SE-20
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Autophon SE-20
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Control panel
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SE-20 with battery removed
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Autophon SE20 in leather case with carrying strap
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The SE-20 and the SE-160C

The SE-20 is housed in a strong die-cast aluminium body that measures 15 x 9 x 2.5 cm. When the battery is attached at the bottom end, the total length is extended from 15 to 24.5 cm. And when the crypto module is also present, like on the one shown below, the complete radio without the knobs and the antenna socket, measures 24.5 x 9 x 4.5 cm and weights no less than 1.3 kg.

The radio features up to six crystal-operated channels. The Power switch offers three volume levels, plus a silent mode. A small red LED, mounted in between the power and channel selector, is lit when the radio is transmitting. The same LED flashes when the battery is almost empty. At the left side is a large push-to-talk (PTT) switch, plus two buttons for selective tone calls.

When the crypto module is present, an additional two-position rotary switch is present at the control panel, allows the user to select between clear (CL) and crypto (CRY) mode. Furthermore, a 5-pin LEMO socket is available at the left side, for connection of a Vericrypt key loading device.

  • VHF-L 1
    68 - 88 MHz
  • VHF-H
    138 - 174 MHz
  • UHF
    400 - 470 MHz
  1. In Motorola-terminology, the VHF-L band is also known as MIDBAND.

Voice encryption   Vericrypt
The expanded version of the SE-20 belongs to the first generation secure voice equipment. It features a time-domain voice scrambler rather than real (digital) speech encryption, and offers only limited protection. For this reason, voice scramblers are often classed as privacy units.

The actual voice scrambler unit of the SE-20 was developed and built by the Swiss manufacturer Brown Boveri and Company (BCC). It was nearly identical to their Vericrypt 1100 system. After sampling the sound, it cuts the speech into short time fragments of 30 ms each, which are then scrambled in a complex ever-changing order.

The pattern in which the audio fragments are scrambled, is determined by a cryptographic key, that is loaded into the unit by means of a Vericrypt 1102 key loader, that should be connected to the LEMO socket at the left side.
Vericript 1100 with key loader connected

Vericrypt was used extensively by police forces in Europe during the 1980s, and initially offered reasonable protection against eavesdroppers, but this changed when hackers discovered that the audio fragments still carried the properties of human speech. And with the availability of micro­processors, it was only a matter of time before the original speech could be reconstructed again.

No matter how complex the pattern in which the time fragments are scrambled, voice scramblers are inherently unsafe. Even the later frequency and time domain scramblers, also known as F/T scramblers, can be broken with relative ease. This problem was solved on the later SE-160-C (shown below), which featured digital speech encryption and was much smaller than the SE-20.

 More about the BBC Vericrypt 1100
 More about the SE-160C

The SE-20 next to its much smaller successor, the SE-160C, which featured digital encryption.

Rechareable NiCd battery Leather carrying case Flexible rubber antenna Key loading device
The SE-20 is powered by a rechargeable AK-20 NiCd battery that should be attached at the bottom of the radio. The battery measures 9.4 x 9 x 2.5 cm and can be charged in situ with a suitable desktop charger.   

Carrying case
The SE-20 is usually carried in a matching leather carrying case, such as the one shown in the image on the right. Note that radio's which have the encryption unit fitted (such as the one featured here), require a larger carrying case.

The image on the right shows the crypto-capable SE-20 in a suitable leather carrying case. A nylon strap allows the leather case to be carried around the neck or on the shoulder.
Locked in the leather case

Depending on the frequency band for which the radio is made, a flexible whip antenna, or a rubber helical antenna should be fitted on the TNC socket at the top of the radio.

The image on the right shows two such antennas. The ticker one at the left is for the 68-88 MHz range (VHF-L) and the one on the right is for the UHF version (400-470 MHz).
Antennas with TNC base, suitable for the SE-20

Key loader
The secure speech module of the SE-20 was made by Brown Boveri and Company (BBC) in Switzerland, and was compatible with their range of Vericrypt voice encryption units, also known as the SV12-1100 series.

The scrambling pattern of the time-domain voice scrambler is determined by a crypto key, that can be loaded into the radio by means of the Vericrypt 1102 unit shown on the right.

 More about the key loader
Vericrypt 1100 key loader

Battery Battery Autophon SE20 in leather case with carrying strap Locked in the leather case
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Autophon SE20 in leather case with carrying strap
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Locked in the leather case

The interior of the radio, and the voice security module in particular, can be reached via the removable back panel of the unit. Remove six small screws along the edges of the rear side, and take away the panel. This exposes the solder side of the rather large voice scrambler board.

The scrambler board is held in place by six screws along its edges. After removing these screws, the board can be lifted at the bottom end. At the top end, the board is connected to the radio and to its controls via two 14-pin DIL sockets. After carefully removing the connectors from the DIL sockets, the board can be removed.

The board features an existing time-domain voice scrambler, developed and built by the Swiss company Brown Boveri and Company (BBC) and is based on BBC's Vericript 1100 scrambler. Most electronic circuits are identical or similar.
Voice scrambler

All components are mounted on one side of the board, but they are stacked in several places in order to save space. Nevertheless, the board takes the same space as the radio plus its battery. The large brown rectangular parts are potted circuits that were also used in the Vericrypt 1100.

 More about the BBC Vericrypt 1100

Crypto unit opened from the rear Voice scrambler PCB removed from the case Voice scrambler (solder side) Voice scrambler PCB detail - note the three small stacked batteries Hybrid circuits Logic circuits Stacked components
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Crypto unit opened from the rear
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Voice scrambler PCB removed from the case
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Voice scrambler (solder side)
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Voice scrambler
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PCB detail - note the three small stacked batteries
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Hybrid circuits
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Logic circuits
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Stacked components

Model number
The model number is printed on a label at the back of the radio and always starts with the model number: SE 20. The meaning of the remaining parts is given in the diagram below, based on the model number of the radio that is featured on this page. It is constructed as follows [3]:

Use the tables below to decode the actual digits found at the rear of the radio. In our case, the radio covers the 146 to 174 MHz band (16) and has an output power of 2.5 Watts (2).

Frequency band
  • 08
    68-88 MHz
  • 14
    132-148 MHz
  • 16
    146-174 MHz
  • 42
    400-425 MHz
  • 43
    400-440 MHz
  • 45
    425-450 MHz
  • 46
    430-470 MHz
  • 47
    450-470 MHz
TX power
  • 0
    Driver only
  • 1
    1 W
  • 2
    2.5 W
Technical specifications
  • Frequency
    VHF-L, VHF-H or UHF (see above)
  • Output
    1 or 2.5 Watt
  • Power
    7.2 V DC
  • Channels
    3 with XTAL or 200 with PLL
  • Mode
  • Impedance
  • Security
    Digital voice encryption
  • Weight
    1.3 kg
  • Size
    24.5 x 9 x 4.5 cm (without knobs)
  1. Yves Oesch, Autophon SE-20
    Website. Retrieved December 2016.

  2. Freiwillige Feuerwehr Föhrenau, 1980 - 1989
    Retrieved December 2016.

  3. Oppermann Telekom, Ascom SE20
    Retrieved December 2016.
Further information
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Crypto Museum. Created: Sunday 04 December 2016. Last changed: Friday, 23 February 2018 - 21:36 CET.
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