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TST-7698 →
HF 2.4 Kbps Modem with FEC

TST-4045 was a high speed, high performance short wave (SW) modulator/demodulator (modem) for the transmission of digital data via noisy low-quality radio links, with optional data and voice encryption, introduced in the early 1990s by TeleSecurity Timmann (TST) in Tutzing (Germany).

The product is based on a cut-down version of Telefunken's ETM-1820/M ECHOTEL modem. It features Forward Error Correction (FEC), adaptive notch filters, data interleaving, echo cancellation and signal equalization, using the era's latest developments in Digital Signal Processing (DSP).

It could be upgraded with digital encryption by adding an existing TST cipher unit internally. For secure speech, the TST-7698 was added, whilst for data encryption, the TST-5573 was used. The image on the right shows an early prototype that is still marked ETM-1820/M on its front panel.
TST-4045 (ETM-1820M) prototype with handset

The TST-4045 uses a single-tone transmission protocol that conforms to NATO's STANAG-4285 standard, and was intended for transmission of high-speed data, V.24 facsimile, narrow-band secure digital voice, slow-scan TV, and for transmission of direction finder data and telemetry.

The front panel is nearly identical to that of the Telefunken ETM-1820/M, with the exception of the black area at the right, in which an NF-7 audio socket has been added for the device's voice features. The device was sold to the British Army, for which an English brochure was available [A]. The ETM-1820/M ECHOTEL modem was still available from Telefunken Racoms 1 in 2018 [3].

  1. Since 2004, Telefunken Racoms is a wholly owned subsidary of the Israeli company Elbit.

TST-4045 (ETM-1820M) prototype TST-4045 (ETM-1820M) prototype with handset LCD display with original ETM-1820/M marking NF-7 socket for handset, added by TST Controls on the front panel Switches and indicators Bar unit outside the desktop enclosure Rear view
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TST-4045 (ETM-1820M) prototype
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TST-4045 (ETM-1820M) prototype with handset
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LCD display with original ETM-1820/M marking
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NF-7 socket for handset, added by TST
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Controls on the front panel
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Switches and indicators
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Bar unit outside the desktop enclosure
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Rear view

The diagram below shows the front panel of the TST-4045, which is in fact the same as the front panel of the Telefunken ETM-1820 on which it is based, with an additional NF-7 socket fitted at the right. This socket is not present on the Telefunken ETM-1820, and allows a military handset to be connected to the (optional) TST-7698 voice encryptor that can be fitted inside the case.

TST-4045 (ETM-1820/M) front panel

At the rear are sockets for data I/O (X1), a remote control unit (X2) and an HF or VHF/UHF radio (X3). Depending on the version, a EURO socket is present for connection to the AC mains, or a custom socket with an extra fuse for connection to a DC power source in the range 18 to 32 volt.

Note that the company logo at the left, is that of Timmann Tele Security (TST), and not that of Telefunken Systems Technik (confusingly also abbreviated to TST), which was the name that Telefunken in Ulm used for a while, before it was merged with Deutsche Aerospace (DASA) into Daimler-Benz Aerospace. In 2004, part of the old Telefunken radio and train technology division was sold to the Israeli technology firm Elbit and is known today as Telefunken Racoms [3].

The TST-4045 is housed in a 1U 19" rackmount enclosure, that in turn could be fitted inside a desktop enclosure, as shown at the top of this page. The interior can be accessed by removing the screws from the top panel, and lifting the panel carefully from the contact strips at its sides.

The interior is roughly divided into three areas. At the left is the power supply unit (PSU), which in this case is an AC mains PSU. Other power options were also available, each with different connectors at the rear panel. In this case, the holes for the DC power sockets are covered by a blank panel, whilst a common 3-pin Euro-socket is available for connection to the AC mains.

At the center is the actual DSP-based ECHOTEL modem that was developed by Telefunken in Ulm (Germany). The circuit board is in fact an enhanced ISA-bus card that is fitted horizontally.

At the right is Timmann's own optional encryption unit — in this case a TST-7698 digital speech encryptor — that could optionally be added to the set. It is shown here with improvised cabling, indicating that it was indeed a prototype. The connection for the handset is extended to the NF-7 socket in the black area of the front panel, whilst the connection to the radio is available at the DB15 socket marked X3 at the rear. This socket was also used for connection of the key loader.

Interior Interior - front view Interior - rear view PSU Telefunken HF modem with DSP technology Timmann TST-7698 digital voice encryption unit Close-up of the Telefunken modem board AC socket and blank panel covering the holes for the DC sockets
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Interior - front view
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Interior - rear view
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Telefunken HF modem with DSP technology
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Timmann TST-7698 digital voice encryption unit
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Close-up of the Telefunken modem board
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AC socket and blank panel covering the holes for the DC sockets

  • Modes
    Simplex, half-duplex, full-duplex
  • Speed
    75, 100, 300, 600, 1200, 2400 and 3200 baud
  • FEC coding
    Convolutional coding, soft decision
  • Interleaving
    Short, long
  • Modulation
    2, 4 or 8 PSK convolutional
  • Tone frequency
    1800 Hz
  • Multipath
    Tolerance up to 6 ms
  • Bandwidth -25dB
    Max. 3 kHz (0.3—3.3 kHz)
  • Bandwidth -3dB
    Max. 2.4 kHz (0.6—3.0 kHz)
  • Offset/shift
    Up to 3.5 Hz/sec tracking
  • Demodulation
    Coherent with channel matched filter and equalizer
  • Notch filter
  • Mains power
    93—255V AC, 47—400 Hz (≤25W)
  • Battery
    18—32V DC (≤25W)
  • Dimensions
    485 x 465 x 44 mm (including grips), 19" rackmount
  • Weight
    Approx. 4.5 kg
  • Temperature
    -10 to +55°C (operation), -30 to +70°C (storage)
  • Data
    EIA RS-232C, DIN 66020, CCITT V.24.V.28
  • Control
    EIA RS-232C, DIN 66020, CCITT V.24.V.28 (internal connector)
  • Speed
    75, 150, 300, 600, 1200, 2400, 4800, 9600 baud asynchonous
  • Audio
    0dBm, -20dBm to +6dBm (adjustable), 600Ω
  • 46
    18—32V DC power supply instead of AC PSU
  • 47
    High security ciphering option for V.24
  • 51
    Selective call option for DTE 1 software
  • 52
    Built-in vocoder option for digital voice
  • 53
    Built-in vocoder option for digital secure voice 2
  1. DTE = Data Terminal Equipment.
  2. Uses the TST-7698.

  1. TST Telesecurity Timmann, TST 4045 brochure
    Sales brochure (English). 4 pages. Date unknown.

  2. TST 7698 sales brochure 1
    Date unknown. 6 Pages (German).

  3. TST 7698 handbook 1
    8.20 F. TST, 1988. 38 Pages (English).
  1. Kindly supplied by Jim Meyer [1].

  1. Helmut 'Jim' Meyer, HS0ZHK, My way to Ham - Radio and beyond
    Website QRZ.COM. Personal correspondence. Retrieved February 2018.

  2. Anonymous, ETM-1820/TST-4045 prototype - THANKS !
    Received June 2014.

  3. Telefunken Racoms, ETM 1820M
    Retrieved February 2018.
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Crypto Museum. Created: Wednesday 03 July 2013. Last changed: Tuesday, 20 March 2018 - 14:08 CET.
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