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Voice Telsey
Narrow-band radio voice encryptor
The TX-1020C and the TX-1020C Mk. III are
voice encryption devices for use on
narrow-band FM radio links, developed in the late 1980s
by Telsy in Turin (Italy).
The devices were commonly used in combination with VHF/UHF FM
simplex radios,
such as the ones used by the police. It is also suitable for use on
shortwave (SW) radio links, and offers analogue and digital
encryption modes.
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Many different versions of the TX-1020C exist.
In fact, there was a variant for a wide variety of
mobile radio brands and models. As each model may
have different audio levels, impedances and channel characteristics, the
circuitry of the TX-1020 had to be tailored for that. It was usually
connected instead of the existing handset.
The image on the right shows a version that was made especially for
ASCOM radios used with the Dutch Police, as indicated by the
designator at the back.
It was optionally housed inside another case (see below), together with a
small amplifier.
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When used unmodified, the TX-1020C was connected to the radio instead of the
existing microphone or handset. It effectively takes over the function
of the microphone, and has a Push-To-Talk switch
(PTT) at the left.
On top of the unit are two buttons, marked 1 and 2, for selection of the
appropriate (pre-defined) cryptographic key. To the right of these buttons
is a socket for the connection of an external key-filler. The TX1020 also takes over the function of the speaker.
When used outside Italy, encryption devices like the TX-1020C required
an export licence during the 1980s and 90s. For most devices this would
usually take one month, but in case of the TX-1020C Mk. III it could take
up to 90 days [2].
Around the same time as Telsy developed the TX-1020,
Philips Usfa (Netherlands) developed a device that
showed great similarity. It was called ORTHROS,
and was also intended as an add-on for existing radios, but was never released.
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The diagram below shows the layout of the TX-1020. The device looks like
an extended handheld microphone of a mobile radio. It measures 14 x 7 x 4
cm and weights 280 grams. It is connected directly to the VHF/UHF two-way
simplex radio (sometimes via an external interface) and takes over the function
of the microphone and the speaker. Power must be provided by the host radio.
Keys are loaded into the device via a
6-pin Hirose socket at the top
(the so-called fill connector). Up to 4 cryptographic keys can be stored.
The small keypad is used to select the required key and to adjust the
volume of the speaker. The largeswitch at the left side is the Push-To-Talk
(PTT).
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The TX1020 can hold up to 4 encryption keys, each of which can be assigned
an encryption mode, which can be analogue or digital [A]. The following
encryption modes are available:
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- Analogue
In this mode, the TX1020 is a 2-dimensional
frequency and time domain voice scrambler,
based on Fast Fourier Transformation (FFT). Synchronisation
is not necessary in this mode. It provides reasonable security and works
well, even under bad conditions. This signal works within the 3 kHz
bandwidth of a speech channel (300-3100 Hz).
- Digital
In this mode, the TX1020 uses a digital speech encryption that works within
the bandwidth of a speech channel (420-2830 Hz). Speech is first digitized
by means of an LPC-10 vocoder, and then encrypted digitally. An eavesdropper
will only hear noise on the channel. Synchronisation is necessary in this mode,
and takes several seconds.
- Analogue HF
This mode is similar to the standard analogue mode (1) but is suitable for
narrow-band HF radio channels (short wave). It is not suitable for
VHF/UHF FM radios.
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In terms of cipher security, MODE (2) is clearly the better one, as it is
the only one that provides true encryption. It has the disadvantage that
synchronisation takes several seconds when the connection is first opened.
Once synchronised, it stays in-sync for several minutes. The analogue modes
(1) and (2) are faster in operation, but are far less secure.
In general, voice scramblers,
no matter how complex, are inherently insecure
and can be broken by professionals within seconds.
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Crypto keys can be entered via the keypad of the TX-1020 (handheld
or base station variant), or by means of the external
INJ-5000 key entry device,
also known as a code-injector. With the mobile variant
of the TX-1020, the custom-specific keys were programmed by the manufacturer.
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The TX-1020C and the later TX-2020C could be used
in combination with a wide variety of mobile radios, such as
Motorola,
Philips,
BBC
and ASCOM.
Is some cases, the TX-1020 could be used without
modification, simply by using the appropriate cable, but in some cases
an additonal modification inside the radio was required.
The latter mainly involved power and squelch wiring.
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The image on the right shows a Telsy TX-1020C built inside a custom case,
together with some additional electronics. The top lid of the case contains
a number of spring-loaded buttons that indirectly operated the buttons on
the Telsy device below them. The SPEAKER-button was omitted.
The LCD display was visible through a window in the case, just above the
buttons.
An additional PCB is mounted inside the case to the left of the Telsy TX-1020C.
It is marked ASC9126A1 COMP., indicating that it was probably developed by
ASCOM in June 1991.
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The short cable from the TX-1020 is connected at various places on the board,
and the board is connected to the outside by means of a male DB15 connector
at the front left. A metal frame on top of the outer case was probably used
as a mounting bracket inside a (police) car.
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The TX-1020C is easily opened by removing 6 bolts at the rear. The rear
panel comes off and the interior becomes visible.
The interior consists of two PCBs: the main PCB that contains all electronic
circuits, and a small daughter card that acts as the cable assembly.
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The cable assembly is held in place by 4 screws and is connected to the
main PCB by means of a so-called zebra-connector. The image on the right
shows the cable assembly separated from the main PCB. The gold-plated
zebra-connector is visible at the center of
the main PCB.
The TX-1020C is built around a
TMS-320 DSP controller by Texas Instruments,
the same one as used in the earlier TX-900, albeit
in a square package. It is partly covered by an orange flex-PCB.
The TMS-320 is driven by a 20MHz crystal.
More detailed images below. Click to enlarge.
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The small daugther card that was used as the cable assembly, was designed
in such a way that it could easily be modified for a particular radio.
Many different versions of this PCB existed, complete with a matching
cable (see below).
The one shown here has an extra two wires that are connected to the
orange flex PCB inside the unit.
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As stated before, the TX-1020C MkIII was usually supplied to the
customer ready for connection to a specific radio. In such cases
the appropriate cable assembly was already installed in the unit.
The list below shows which radios were supported. The radios that needed
a small modification, are marked with a tick in the column 'Modify'.
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