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Telsy TX-1020C
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/UFH 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.

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. The unit was usually connected instead of the mike/speaker.

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.
Telsy TX1020C

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.

Telsy TX1020C Overview of the controls Operating the TX1020C Type plate showing that this is the ASCOM-variant Close-up of the keyboard Close-up of the display Selecting a pre-set key Fill connector
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Telsy TX1020C
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Overview of the controls
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Operating the TX1020C
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Type plate showing that this is the ASCOM-variant
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Close-up of the keyboard
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Close-up of the display
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Selecting a pre-set key
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Fill connector

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.

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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).

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:

  1. 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 inferior circumstances. This signal works within the bandwidth of a speech channel (300-3100 Hz).

  2. 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.

  3. Analogue HF
    This mode is similar to the standard analogue mode (1) but is suitable for narrow-band shortwave radio channels. It is not suitable for VHF/UHF FM radios.
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.

Cryptographic keys
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.

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.

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.
Telsy TX-1020C mounted inside a custom case (ASCOM)

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.

Telsy TX-1020C built inside a custom case Telsy TX-1020C mounted inside a custom case (ASCOM) Close-up of the ASCOM case Connector on the ASCOM case
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Telsy TX-1020C built inside a custom case
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Telsy TX-1020C mounted inside a custom case (ASCOM)
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Close-up of the ASCOM case
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Connector on the ASCOM case

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.

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.
Cable assembly removed

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.

TX-1020C interior Cable assembly separated from the unit Cable assembly removed TX-1020C interior (cable assembly removed) TMS320 DSP by Texas Intruments 10 MHz crystal Connector for cable assembly Unknown microcontroller
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TX-1020C interior
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Cable assembly separated from the unit
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Cable assembly removed
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TX-1020C interior (cable assembly removed)
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TMS320 DSP by Texas Intruments
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10 MHz crystal
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Connector for cable assembly
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Unknown microcontroller

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'.

Manufacturer Radio model Telsy cable assembly Modify HF INT800
Alcatel 9220HT 425TX-202-N321 - - -
Ascom SE140 425TX-202-N201 - - -
Autophon SE20 425TX-202-N061 - - -
Autophon SE120 425TX-202-N021 - - -
Autophon SE156 425TX-202-N041 - -
BBC Veriport 1400 425TX-202-N181 - -
BBC Veriport 1900 425TX-202-N031 - - -
BBC Veriphon RT61 425TX-202-N021 - -
Elmer RH4/178 425TX-202-N281 -
Elmer RT-633 425TX-202-N421 - - -
GE PE 425TX-202-N221 - -
Harris RF230 425TX-202-N071 -
ICOM IC-U200T 425TX-202-N301 - -
Italtel MB70 425TX-202-N101 - -
Italtel MB70-D5 425TX-202-N331 - - -
Italtel MB70-D5 425TX-202-N121 - -
Johnson FM5852 425TX-202-N241 - -
Johnson 7151 425TX-202-N251 - -
Kenwood TS50 425TX-202-N451 -
Midland 70-440 425TX-202-N041 - -
Motorola MX300 425TX-202-N171 - -
Motorola MX1000 425TX-202-N231 - - -
Motorola MX2000 425TX-202-N194 - - -
Motorola Radius P210 425TX-202-N351 - -
Motorola MC-MICRO 425TX-202-N291 - - -
Motorola MC-MICRO 425TX-202-N061 - -
Motorola Radius GM300 425TX-202-N131 - -
Nokia RC58 425TX-202-N271 - - -
OTE HP 9000 425TX-202-N401 - -
OTE P80-C 425TX-202-N161 - - -
OTE RMT 246 425TX-202-N411 - - -
Otema S-80 425TX-202-N141 - -
Philips FM1000 425TX-202-N151 - - -
Philips PFX 425TX-202-N011 - -
Prodel V5/32 425TX-202-N081 - - -
Prodel P7/32 425TX-202-N091 - - -
Radiosystem PR460 425TX-202-N341 - -
Siemens ER95A/1 (RV3) 425TX-202-N101 - -
Siemens RV3 425TX-202-N111 - -
Storno CB911 425TX-202-N211 - - -
Storno Stornophone 6000 425TX-202-N091 -
Tadiran RT7330S 425TX-202-N361 - -
Transworld RT100/MP 425TX-202-N391 - -
Teletron FUG 8B-1 425TX-202-N051 - - -
Telettra RH6 425TX-202-N311 - -
Thomson ATR410 425TX-202-N121 - - -
Thomson ATR427 425TX-202-N011 - -
Thomson ATR430 425TX-202-N261 - - -
Thomson ER75 425TX-202-N031 - - -
Thomson TMF213 425TX-202-N111 - -
Thomson TMF300 425TX-202-N441 - -

A tick in the column 'HF' indicates that the HF-circuit of the radio needed to be modified. The rightmost column, marked 'INT800' indicates that the radios are interfaced via a small mobile box adapter that contained an amplifier for an external speaker, together with some interfacing.

In addition to the above pre-assembled cables for specific radio sets, a connector-less universal cable was available for those customers that had sufficient technical background to interface the TX-1020C to their radio. The cable is wired as follows:

Colour Name Function Remark
Outer shield SHLD1 Shield Case (housing)
Black GND Power (-) Also PTT ground
Red +VDC Power (+) 6.5 - 30 Volt
Inner shield GND Ground -
Blue PTTP PTT positive +VDC in TX
Mauve PTTN PTT negative GND in TX
White MIKE1 Mic out 600 ohm balanced and insulated, 4Vpp
Yellow MIKE2 Mic out Return
Brown RXIN1 RM input 600 ohm balanced and insulated, 1Vpp
Green RXIN2 RX input Return
Grey SQLCH Squelch input for VHF, UHF (GND to lock)
  1. Gebruiksaanwijzing Telsy Crypto TX1020
    MAN.FP.1020V311.01. User Manual (Dutch).
    Ascom Teletron BV, January 1991. Issue 1. 6 pages.

  2. Apparato Crypto TX-1020 - Manuale Tecnico 1
    Technical Manual (Italian).
    Telsy S.p.A., Torino, January 1991. Issue 2. 77 pages.
  1. Document kindly provided by Miguel Bravo. November 2017.

  1. Barry Wels, Telsy TX-020C - THANKS !
    February 2011.

  2. Telsy S.p.A., Overview of radio sets supported by TX-1020C
    Correspondence between Telsy and unknown party. Date unknown.

  3. Texas Instruments, TMS320 First-Generation Digital Signal Processors (DSP)
    Datasheet, January 1987.
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Crypto Museum. Created: Friday 02 March 2012. Last changed: Friday, 03 July 2020 - 11:47 CET.
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