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4 frequency diplex system used by organizations such as Interpol and United Nations and the government Diplo services of countries such as Australia, Denmark, Holland, Norway, Pakistan and Spain. Typically runs at 100 and rarely at 200 or 300 bd. This 2 channel system supports several different shift parameters and word, bit, character or not-interleaved of the channel characters but is easy to identify because of its 4 peak signal. This system was developed by Thrane and Thrane of Denmark.


This is a 2 channel simplex asynchronous BAUDOT signal also referenced as TWINPLEX. Its form, according to CCIR Recommendation 346-1, is: "4 Frequency diplex systems" (Dusseldorf, 1990). This is a 2 channel 4 tone diplex asynchronous signal usually consisting of 2 channels of ITA-2 baudot running at the same speed (or according to Rec. 346-1 1 channel BAUDOT/1 channel morse code). According to the recommendation both channels are often scrambled and no loggings of this form have been found to date.


  • F7B4


  • go2decode
  • go2monitor
  • Hoka Code 3-32P
  • Hoka Code 300-32(P)
  • Wavecom W-Code
  • Wavecom W-Spectra

Audio Sample / Waveform

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