Station radio-amateur ON4NB
membre du GDV, "Gang de Verviers"
QRA-Locator : JO20WN
Digimodes, PSK31, SIM_PSK 31/63

Contact :













































































Description of new digimode: SIM_PSK
Name of software: SIM_PSK
Development: 2014
Conceived by : NIZAR BEN REJEB
Origine : Tunisia.
First Issue: October 2014
Modes : BPSK 31 and 63 bps (125 also foreseen ).
Modulation : DBPSK « Differential Binary Phase Shift Keying ».
Pulse shape : Similar to classic BPSK31
Bandwidth : About 60 Hz
Demodulation : Coherent demodulation
Synchronization : automatic on signal
Error correction : FEC (Forward Error Correction)
tolerates one error bit per character
Convolution code : NO (it makes the synchronization too slow)
Interleaved: YES
Repetition : YES, but only for some messages structured as CQCQ, QRZ, QRALOC, NOM, QTH,
Drift tolerance : 20 Hz/min (depending on signal level)
Lower limit of intelligibility: -15.5 dB in text mode. Until -17dB in message mode (in presence of white noise with a bandwidth of 3 kHz)
Reception mode : indifferent (LSB or USB) Note: The frequency adjustment is simplified by staying in USB on all bands
Characters set :

53 "fixed code" A..Z 0..9 <CR> <SPACE> . , : - = + ? ' ( ) ! / @ # *
No character reset on error nor wait character (). Lowercase characters are converted to uppercase,

Special Characters : The special characters such as "É" are converted into standard capitals characters (in this example: "E") but can be displayed in lowercases locally
Messages: The messages used by the ham-radio are coded and structured.
Speed : 187 char/min ( or 31.25 wpm)
Principle :

"varicode" able to encode characters, words and full sentences.
S I M = Structured Integrated Message BPSK31.

Structure : variable code length, from 10 to 100 bits
according to characters… words… sentences.
Software availability since October 2014 on .

Advantages :

  • Varicode optimized : less sensitive to noises by the use of interleaved fields
  • Error Correction: by FEC (Forward error correction).
  • Digital Squelch based on signals coherence.
  • Very fast transmission due to coding whole sentences.
  • Gain of 5 dB on an analog PSK (decoding of signals imperceptible on a waterfall).
  • Mode "split", allowing to use an independent frequency, for receiving and transmission (in the same band).
  • Automatic centering on the selected frequency, by a mouse click.
  • Displaying the "Eye diagram".
  • No special installation. Just copy the exe file or, if necessary, copy / unzip the .RAR file, and paste it where you want .
  • Permanent evolution, responding to users requests.
  • Hyperlink to "DX Cluster" and "PSK-reporter." announcing in real time via Internet the presence of the station using the SIM mode, and where it is received.

  • Eye diagram :

    Instant confirmation of the correct setting:

  • Signal Type : conformity of modulation, PSK, QPSK, FSK, etc..
  • Speed : Compliance of bitrates, 31.25 Hz ... 62.5 Hz ( 125…)
  • Accuracy : bit synchronization, immediate detection of a drift on the diagram....
  • Monitoring : decoding quality, visible distortions in place of straight lozenges
  • Diagnostic : identification de défauts éventuels.

    A click on a crest and here is what looks like the “eye diagram” for proper reception
  • • The straight shape of the lozenges confirms that it is a correct PSK mode.
    • The frequency is correct (cursor centered on crest) no interference.
    • Good binary synchronization signal (diamonds do not slip).

    • Hereunder , no signal received... the eye diagram does show only noise.

    • Receiving a signal PSK31... ( Strong signal, no QRM )
    • wrong selection of mode PSK63, so that it displays only half of a diamond.

    • Receiving a signal PSK63... ( Strong signal, no QRM )
    • Wrong selection of mode PSK31, so that it displays twice the lozenges.

    • Explanation of the eye diagram
    • The cursor is not on the frequency of the received signal.

    • Summary charts describing :
    • First view : signal and bitrate are ok
    • second diagram : signal is 31Hz, but choosen bitrate is 63 Hz
    • Third diagram : signal is at 63 Hz but choosen bitrate is 31 Hz
    • below: bandwidth for 31 and 63 Hz

    SIM31 - SIM63 


    Optimisé pour un affichage en 1024 x 768 points Dernière mise à jour: 19/05/2019