New release of MULTIPSK (4.41) - C4FM #Multipsk

Patrick Lindecker

New release of MULTIPSK (4.41)




Pour les francophones: la version en français de ce message se trouve sur mon site ( Il suffit de cliquer sur le lien "Principales modifications (courriel avertissant de la sortie de la nouvelle version)".

Hello to all Ham and SWL,


The new release of MultiPSK (4.41) is on my Web site (
The mirror site is Earl's, N8KBR:

The MD5 signature of the downloaded MULTIPSK_setup.exe file to, possibly, check (with WinMD5 for example), that the downloading works without error, is equal to: d7da72d36648204bdec1620ce65ea6bb

Multipsk associated to Clock are freeware programs but with functions submitted to a licence (by user key).


The main improvement of MULTIPSK 4.41 is the following:


C4FM decoding (but not the voice)


"C4FM" is the acronym for "Continuous 4 Level Frequency Modulation". This mode has been developped by Yaesu. It is used in VHF and in UHF, mainly for voice communication but also for data communication (included during voice transmissions). It is spread in a mondial net by using, among other means, repeaters and Internet ("VoIP" ("Voice over IP) system called "WIRES-X"). It is a mode for amateurs but professionally developped, at equipement level. It is considered as a professional mode by Multipsk (but the decoding is not limited).


There are two sub-modes really used:

·                     Voice/data mode type 2 (called "Digital Narrow" on the FT991 transceiver),

·                     Voice full rate mode (called "Voice Wide" on the FT991 transceiver).


It is here only considered the data communication which summarizes to callsigns.

Note 1: the Ham position can be transmitted but it is coded and not described, so not decoded.

Note 2: the voice communication decoding is excluded because it needs an AMBE+2 Codec (under a proprietary licence).


For Hams and SWL, the C4FM signal can be received:

·                     either from the discriminator output of a classical VHF/UHF FM receiver via a direct connection to the PC sound card. However, the receiver must have a large reception bandwidth due to the high modulation speed,

·                     or with a SdR receiver (FunCube Dongle, RTL SDR,...) and directly demodulated by Multipsk. It is the simplest solution.


Here is the WEB address where you can know where all C4FM repeaters are located, with their frequencies, for each country:


This mode is in freeware, so without time limitation.


See general specifications below.



Note about translation of Multipsk.exe and Clock .exe:  the 4.40 version of Multipsk has been translated to Spanish by Joachin (EA4ZB), from French.






Description of the C4FM mode

Baud rate: 4800 (with 2 bits per symbol so 9600 bps)


Modulation : each double logic signal (dibit) directly modulates, through a root raised cosine filter (to reduce the bandwidth needed), the VHF or UHF frequency in FM (on about +/- 6 KHz). So this signal is received in base band after FM demodulation.


Reception mode: FM


Character set : on 8 bits


Shape of pulse : root raised cosine filter (Alpha=0.2)


Bandwidth : about 12 KHz


Synchronization : automatic using the signal


Detection code: yes on 40 bits.


Convolution code: FEC R=1/2, k=8


Other code used: Golay (24,12,8)


Interleaving : yes


Scrambling: yes


Each C4FM packet contains different "channel":

·                     a "Header" of 960 bits for call signs and different pieces of information about the transmission,

·                     a certain number of "Communication" (of also 960 bits) which contains mainly the digital voice but also data,

·                     a "Terminator" identical to the "Header".


Each "channel" of 960 bits begins with a frame synchronization of 40 bits followed by a frame information of 200 bits relative to the transmission. Afterwards, it is found several "Data channel" and, possibly, "Voice extent channels" (only for "Communication channels"), for a sub-total of 720 bits.


For more details, see the Internet address:


For about the interface between your PC and your transceiver, see the paper "HOW_TO_DO_DIRECT_DSTAR_BETWEEN_HAMs_Rev_A.pdf" located in the file, but taking into account only the reception part (no C4FM transmission by Multipsk).


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