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← Ascom
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].
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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.
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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.
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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.
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VHF-L 1 68 - 88 MHz VHF-H 138 - 174 MHz UHF 400 - 470 MHz
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In Motorola
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terminology,
the VHF-L band is also known as MIDBAND.
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Voice encryption
Vericrypt
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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.
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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.
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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.
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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).
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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.
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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.
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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).
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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
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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 FM Impedance 50Ω Security Digital voice encryption Weight 1.3 kg Size 24.5 x 9 x 4.5 cm (without knobs)
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© Crypto Museum. Created: Sunday 04 December 2016. Last changed: Friday, 23 February 2018 - 21:36 CET.
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