After the end of World War II, Dr. E. Gretener developed the tape teleprinter "Single tone combination printer (ETK)" on his own initiative. The ETK is based on a fourteen segment code and printing head. In contrast to Baudot code CCITT No. 2 which is used in standard landline and radio teletype machines, in which the omission of one sigle bit will cause a letter to be illigible, the letters based on the fourteen segment code are usually still discernible, of one segment is missing due to fading effects or poor landlines.
The early ETK models have only been used in landline connections, only the later variant ETK-R (Model 55) could be used in wireless connections due to improved filtering.
A ciphering machine Telecrypto 53 could be added to a ETK printer setup for automatic encrypted radioteletype communications. The lack of synchronisation of the ciphering machine Telecrypto 53 made wireless communications quite unreliable. The omission of one single step caused the ciphering systems at the transmitting and receiving site to loose synchronisation, the printed output became illegible, the ETK did "print Chinese"...
When the successor system Krypto - Funkfernschreiber 58 (Ciphering radioteletype system 58) with it's automatic synchronisation was introduced in 1958, the Swiss Army got one of the most sophisticed systems for automatic real time encrypted radioteletype communications in the world.
To replace the bulky Teletype System 34, this came with a fuel operated generator and a total of eight crates, Dr. Edgar Gretener developed in the last years of World War II a compact paper tape teletype printer, the "single tone combination printer" ETK.
In contrast to a standard teletype printer, in the ETK, a fourteen segment code printed on a paper tape using a printer wheel is used. If one of the segments is lacking, the character can still be recognized in most cases. This makes the ETK system more reliable under difficult transmission conditions. Radioteletype systems using the Baudot code CCITT No.2 print wrong characters if one of the bits of the transmitted characters is missing. This is of much importance in the cases, where numbers are transmitted.
A first batch of fifty ETK machines model 47 was delivered for wired communications in the year 1947, the set saw some improvements for the model 50, which was more reliable.
Because of the system was failing quite often in encrypted wireless communications due to a lack of synchronisation, the "War Technical Department" ordered an improved version. In a modem, a frequency shift audio signal was generated to drive a transmitter with grid modulation in telephony / AM mode, and so to circumvent the use of direct frequency shift keying of the transmitter.
The ETK consists of a transport box with an integrated amplifier, in the model ETK-R 55 the electronics of the modem and the printing system with the character printing wheel.
The amplifier in the transport box has to be connected to the audio output of the receiver and the microphone input jack of the transmitter. A multipole cable is used to connect the amplifier / modem to the printing machine.
The Swiss Army high power stations G1,5K / SE-302, M1K / SE-403 and SE-406 can be used for encrypted communications with the ETK printer connected to the
Telecrypto 53, also made by Gretag company.
Because of omitted character bits due to fading or other propagation disturbances, the ciphering machines at the receiver and transmitter sites loose synchronisation and the following part of the message become illigible. The message had to sent a second time. This was improved with the punched tape transmitting unit 55, which came with a synchronisation option to overcome short dropouts.
The tape teletype printer Siemens T. typ. 68 was used to generate the punched paper type, the text was printed in plain text on a paper tape when keyed in.
A very similar technology (keyboard, 14 segment code tape printer, synchronisation unit and ciphering machine) in one single quite compact machine was used in the legendary Krypto - Funkfernschreiber KFF 58/61 (Ciphering radioteletype system).