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CHX-200 was a high-end military HF radio station, developed in the late 1970s by Siemens AG in München (Germany) and several other parties, for use by the German Army, the Bundeswehr. The system went into production around 1981 [2]. The system has a modular design and can be used in many different configurations, making it suitable for morse code (CW), voice (phone) and data.

At the heart of the system is the CHX-200 RX/TX unit, which consists of a receiver with a built-in exiter. By adding an external HF power amplifier (PA), the station can be configured for short-range, mid-range or long-range applications.

It could (optionally) be expanded with features to reduce the risk of interception and location, and to improve data integrety, such as SITOR, ARQ, FEC, Frequency Hopping, Burst Transmission and Data Encryption. The image on the right shows a mobile setup with a CHX-200 RX/TX (bottom left), a CHP-200 Processor (top left) and a PA [1].
CHX-200 RX/TX (bottom left), CHP-200 Processor (top left) and Power Amplifier. Photograph kindly supplied by Jim Meyer [1].

Due to the highly modular design of the system, it was suitable for a wide variety of military HF applications, including Reconaissance and Special Forces — using the manpack configuration — battalion level communication — using a mobile setup — and full base station communication.

Within the Bundeswehr, the 400 Watt version of the CHX-200 was used in fixed C2 2 bunkers, as well as in mobile communications shelters — commonly fitted on the back of a military truck — with the CHO-902 magnetic loop antenna at the roof. Apart from the Bundeswehr, the CHX-200 was used by the German Meteorological Services, and by the armies of other NATO countries.

  1. The CHX-200 is sometimes classed as an Emergency Communications set (ECCOM), but this is not the full story. Whilst it was used as an ECCOM by the German Government, it found a much wider application.
  2. C2 = Command and Control.  Wikipedia

Complete mobile CHX-200 setup. Photograph kindly supplied by Jim Meyer [1] CHX-200 manpack setup. Photograph kindly supplied by Jim Meyer [1] Setup with CHO-902 magnetic loop antenna and antenna control unit. Photograph kindly supplied by Jim Meyer [1] CHX-200 with DSP modem. Photograph kindly supplied by Jim Meyer [1] CHX-200/F1 modem. Photograph kindly supplied by Jim Meyer [1] CHO-200 controller. Photograph kindly supplied by Jim Meyer [1] CHO-200 controller (connections). Photograph kindly supplied by Jim Meyer [1] CHX-200 RX/TX with CHP-200 Processor. Photograph kindly supplied by Jim Meyer [1]
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Complete mobile CHX-200 setup. Photograph kindly supplied by Jim Meyer [1]
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CHX-200 manpack setup. Photograph kindly supplied by Jim Meyer [1]
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Setup with CHO-902 magnetic loop antenna and antenna control unit. Photograph kindly supplied by Jim Meyer [1]
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CHX-200 with DSP modem. Photograph kindly supplied by Jim Meyer [1]
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CHX-200/F1 modem. Photograph kindly supplied by Jim Meyer [1]
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CHO-200 controller. Photograph kindly supplied by Jim Meyer [1]
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CHO-200 controller (connections). Photograph kindly supplied by Jim Meyer [1]
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CHX-200 RX/TX with CHP-200 Processor. Photograph kindly supplied by Jim Meyer [1]

Cold War
During the Cold War, the CHX-200 was also used for the Secret Emergency Radio Network 1 of the West-German Government. They were installed in secret underground bunkers — for the Chancellor and the Prime Ministers of the 10 German Counties 2 — that had to survive a possible war with the Warsaw Pact. Each bunker had everything that was needed to survive a nuclear war for several weeks, such as food, electricity generators, fresh-air systems, fallout filters, etc.

Each nuclear bunker also had a fully equipped radio station, with a 1kW transmitter and separate receivers — all connected to camouflaged antennas — using Siemens T-1000 teleprinters for the exchange of messages. The messages were encrypted with the software-based CHP-200.

In addition, there were many trucks that could be used as a mobile Command and Control (C2) centre, equipped with 100W or 400W CHX-200 configurations. It is known that mobile tests were carried out in various countries around the world, including in Indonesia and in Thailand [1].

After the fall of the Iron Curtain from 1989 onwards, the reunification of East and West Germany in 1990, and the subsequent collapse of the Soviet Union in 1992, the Cold War was over and the secret emergency network was no longer needed. The nuclear bunkers and the mobile stations were dismantled, and most of the high-end radio equipment was scrapped. Only a small number of Siemens CHX-200 radio stations are now in the hands of collectors and radio amateurs.

  1. German: Notfunknetz der Bundesregierung und der Landesregierungen.
  2. German: Bundesländer.

  • CHX-202 · low power
    This is the manpack version of the CHX-200, which consists of the CHX-200/RX/TX, and the AM-921/GY 20W RF amplifier (the latter made by TELEMIT in München, Germany).

  • CHX-210 · medium power
    This is the CHX-200/RX/TX combined with the 100 Watt PA-100 Amplifier, the ATU-100 automatic antenna tuner and a PS-100 mains power supply unit.

  • CHX-240 · high power
    In this setup, the CHX-200/RX/TX is combined with the 400 Watt PA-400 Amplifier and a 400 Watt ATU-400 automatic antenna tuner — both made by Rohde & Schwarz 1 — and a PS-400 mains power supply unit.

  • CHX-250 · very high power
    This is the very high power version of the CHX-200, in which the exiter is combined with the 1 kW fully transistorised PA-1000 power amplifier, the CHP-200 processor (or the F1 Modem) and the PS-1000 mains power supply. The PA-1000 was designed for use with wideband antennas, and did not have an antenna tuner.
  1. The PA-400 Power Amplifier and the ATU-400 Antenna Tuner are the same as the ones used with the Rohde & Schwarz XK-405/XK-245 radio station.

CHX-200 RX/TX   Exiter
This is the basic transceiver, which consists of a receiver and a built-in exiter. It could be combined with a selection of Power Amplifiers (PAs). Two versions of the CHX-200/RX/TX are known, with the later one having a modernised circuit and SQUELCH.

CHX-200/F1 Modem
This is an HF modem that allows transmission and reception of digital information in F1B mode (F1), with a speed of up to 200 baud, using an FSK frequency shift of ±85Hz or ±425Hz. This modem is not used when the CHP-200 Processor is part of the setup.

CHP-200 Processor
This is a (digital) processor that replaces the CHX-200/F1 modem. It makes the CHX-200 radio station suitable for a number of additional ECCM features and communications protocols, such as SITOR, ARQ, FEC, Frequency Hopping, Burst Transmissions and Crypto. For some of the ECCM features, suitable cryptographic keys had to be loaded into the CHP-200 by means of a Key Gun.

The CHP-200 was fully under software control, and it is known that different versions of the software were available, to accomodate the needs and requirements of the various customers.

CHO-200 Control Unit
This is an integral part of the CHP-200 Processor, that controls its mode of operation, checks the security features and raises an alarm if they are not functioning properly. The CHO-200 can be detached from the CHP-200 and mounted in a convenient place.

CHO-902 Antenna
This was a magnetic loop antenna that was suitable for mobile applications. As such, it could be mounted on the roof of a truck or a communications shelter. The antenna came with the CHO-902 Antenna Control Unit.

PA-400 Power Amplifier
This is a 400W power amplifier that can be connected directly to the exiter (CHX-200 RX/TX). It should always be used in combination with the ATU-400 antenna tuner. Both the PA-400 and the ATU-400 were made by Rohde & Schwarz, and were taken from their XK-405/XK-245 radio station.

PA-1000 Power Amplifier
This is a fully transistorized power amplifier, with an output power of 1 kW. It is indended for use in combination with wideband antennas, and does not have or need an antenna tuner. The PA-1000 consists of four individual 50V wideband amplifiers, each of which is built around four MRF-150 transistors — two in parallel in a push-pull configuration — delivering approx. 300W per module. Each module has a MRF-148 in the driver stage. In the output of the PA-1000 are 7 low-pass filters, each of which can be selected by means of PIN diodes.

Key Gun
When using the CHX-200 in combination with the CHP-200 Processor, it was possible to use data encryption and frequency hopping as two techniques to improve security, also known as Electronic Counter Counter Measures (ECCM).

The Siemens Key Gun – shown in the image on the right – was used to load the cryptographic KEYS into the CHP-200. It was common practice to change the KEYS at least every 24 hours.

 More information

Key Gun with NF-7 fill cable

ARQ   Automatic repeat request
Error-control method for data transmission that uses acknowledgements and timeouts to achieve a reliable data transmission over an unreliable medium. Also known as Automatic Repeat Query.  Wikipedia
ECCM   Electronic Counter Counter Measures
Equipment used in secure communications (COMSEC) to protect against counter measures, such as eavesdropping, interception, direction finding, etc. Frequency Hopping (FH) is an example of ECCM.
FEC   Forward error correction
A technique for controlling (and correcting) errors in data transmission over an unreliable or noisy medium, such as an HF radio channel.  Wikipedia
FH   Frequency Hopping
Method for quicky changing the frequency (channel) during a transmission in a seemingly random order. This is done as an electronic counter counter measure (ECCM), to protect the conversation against eavesdropping and interception by the enemy.
RX/TX Exiter
  • Frequency
    1.5 — 29.999 MHz in 100 Hz steps
  • Modulation
    A1, A3H, A3J (LSB/USB), DATA
  • High power
    400W +1/-2dB 1
  • Low power
    70W +1/-2dB 1
  • With load
    > 100W, < 500W (s=2)
  1. Continuous in A1 and F1, Peak power in A3J, A3H and DATA.

  1. CHX-200 sales brochure
    Siemens AG, date unknown, but probably late 1970s. 1

  2. CHP-200 Processor - Beschreibung und Technische Daten
    Description and Technical Specifications (German).
    Siemens AG, date unknown. 1

  3. CHX-200/F1 Modem - Beschreibung
    Short desciption (German). Siemens AG, date unknown. 1
  1. Document kindly supplied by [1].

  1. Helmut 'Jim' Meyer, HS0ZHK, My way to Ham - Radio and beyond
    Website QRZ.COM. Personal correspondence, December 2017.

  2. SIGIDWIKI.COM, Siemens CHX-200 FSK Modem 1
    Retrieved December 2017.
  1. Note that the information on this web page contains many factual errors.

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Crypto Museum. Created: Thursday 28 December 2017. Last changed: Sunday, 11 February 2018 - 21:30 CET.
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