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====== ETK-R 55 ======
**Single tone combination teleprinter, model 55** / **ETK-R 55**; manufactured by [[Gretag|Dr. Edgar Gretener AG, Zurich]].

After the Second World War, Dr E. Gretener developed the tape teleprinter "Einton - Kombinationsschreiber" (ETK) on his own initiative, the teletype procedure is based on his specially developed 14 element code. In contrast to the Baudot Code CCITT No. 2, in which even the failure of one character (for example in a radio transmission with interference) leads to the mutilation of the message, the text in the 14 segment code can usually still be deciphered without any problems even if one segment fails due to poor transmission conditions.

The ETK was initially used on wired teleprinter connections, but the improved version [[ETK-R55]] (model 55) improved the transmission quality on wireless transmission pathes thanks to improved filtering of the radio signal.

The system could be connected to the [[Telecrypto 53]] ciphering machine for real-time encryption, but the lack of synchronisation in the event of an interference or fading during the radio transmission and missing transmission of one single character meant that the rest of the radio message could no longer be deciphered correctly and the teleprinter wrote "Chinese"...

Only with the succeeding set, the [[KFF-58|Krypto - Funkfernschreiber 58]] with its automatic synchronisation, the Swiss Army finally got one of the world's best radio teletypewriters with real-time encryption.

{{:images:gretag-etk-r55.jpg?direct&600|ETK R-55}}
===== Technical data =====
  * [[Principle]]: Single tone combination teleprinter
  * [[Operation modes]]: Single-tone telegraphy, 1500 Hz, 93 baud, max. 295 ZpM

==== Power supply ====
  * [[Mains operation]]: 110-250 V AC mains
  * 12 V direct current

==== Dimensions ====
  * mm, kg

==== Accessories ====

{{:images:gretag-etk-r55-front.jpg?direct&500|ETK R-55}}
===== Mounting material =====
The **ETK-R 55** consists of a transport case with an integrated amplifier and, this is special for the ETK-R 55 model, the electronics for amplifying and filtering the signal and the actual teletypewriter.

The amplifier in the transport case is connected to the receiver's AF output and the transmitter's microphone phony input. A thick multipole cable connects the amplifier / modem to the teletypewriter.

{{:images:gretag-etk-r55-geschl.jpg?direct&330|ETK R-55}}

The modem section in the ETK-R was fundamentally revised and optimised with better filtering for radio teletype connections.\\ 
Operation modes can be used with single-tone telegraphy 1500 Hz ("Radio ETT" setting) or frequency shift keying with space frequency 1245 Hz, mark frequency 1155 Hz ("Radio normal" mode). In addition to the normal "radio" mode, the "radio fading" mode was introduced; a second detector is used to transmit and analyse not only the fundamental frequencies 1255/1145 Hz, but also the first harmonic 2510/2290 Hz, with the stronger signal being fed to the ETK teleprinter.

{{:images:gretag-etk-r55-elektronik.jpg?direct&330|ETK R-55: Modem}} {{:images:gretag-etk-r55-elektronik-inside.jpg?direct&330|ETK R-55: Interior view}}

The components ETK-R55, [[Telekrypto 53]] and punched tape converter [[UG 55]] were used together as **Funk-Fernschreibanlage 55** for the teletype transmission of encrypted messages via the high power stations [[SE-302|G1.5K]], [[SE-404|M1K]] and [[SE-406]].

The punched tape with the messages was recorded in the writing office with the [[Hds-68|Siemens T. typ. 68]] tape teleteleprinter; in contrast to the hand punch previously used for tape punching, a copy of the message could be printed out on telegram tape immediately for the archives.

The UG 55 punched tape converter converted the Baudot code tapes into the 14-segment code of the ETK and was equipped with a synchronisation device that synchronised the transmitting and receiving systems and kept the sets in sync in the event of signal failures. The entire system required a high level of technical understanding on the part of the operating teams at the high power stations.

The system was technically sophisticated and there were still frequent failures in crypto transmissions due to synchronisation problems, but the preliminary work was incorporated directly into the successor [[KFF 58|Krypto-Funkfernschreiber 58/68]] developed by Gretag in very short time. Thanks to this development, a few years later fully automated encrypted radioteletyping with automatic synchronisation of transmitting and receiving station could be implemented.

===== Technical principle =====

==== Tube layout ====

==== Development ====
To replace the [[Schreibtelegraph 34|Teletypewriter 34]] which consisted of a total of eight crates and a petrol generator, Dr E. Gretener developed the ETK single-tone combination teleprinter in the last war years at his own risk.

After introducing the Model 47 and Model 50 single-tone combination teleprinters for wirebound use, an improved version was ordered at the instigation of the "War Technology Department", as the model 50 when used over a wireless connection very often lost synchronisation. 

Thanks to a FSK subcarrier generated in the ETK-R it was possible to directly control a grid-modulated transmitter in telephony mode and the conversion to frequency shift keying of the carrier (FSK) could be avoided, so transmitters without FSK facilities could be used.

==== Use ====
The radio teletype system with the separate sets [[ETK]], [[Telecrypto 53]] and [[UG 55]] was decommissioned in 1970 when the signal units were re-equipped with the [[SE-415]] / [[KFF 58]] combo and the old high power stations were replaced. 

{{gallery>:images?gretag-etk-r55*.jpg&0&80x80&lightbox&showtitle&titlesort}}

===== Technical documentation =====
  * {{ :manuals:etk-r55-gretag-small.pdf |Funktionsbeschreibung ETK-R Fernschreibanlage Mod. 55, Dr Gretener AG}}
  * {{ :manuals:etk-r55-gretag-prospekt.pdf |ETK teleprinter, Dr Gretener AG}}

==== Further information ====
  * The Telecommunications Equipment of the Swiss Armed Forces, Volume 14, Endegeräte vom Morseschreiber zum Laptop, Merker Verlag, Lucerne
  * [[http://armyradio.ch/radio-d/gretag-etk.htm|Gretag ETK on www.armyradio.ch]]
  * [[https://www.hamfu.ch/de/geraete/geraet.php?id=60|Gretag ETK on the Hamfu website]]
  * [[https://www.radiomuseum.org/r/gretener_ein_ton_kombinationsschr.html|Gretag ETK on the website of www.radiomuseum.org]]