New release of MULTIPSK (4.43) - P25 Phase 1 #Multipsk


Patrick Lindecker
 

New release of MULTIPSK (4.43) and Clock (1.11.9)

 

Pour les francophones: la version en français de ce message se trouve sur mon site (http://f6cte.free.fr). 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 (4.43) is on my Web site (http://f6cte.free.fr/index_anglais.htm).
The mirror site is Earl's, N8KBR: https://www.paazig.net/f6cte/MULTIPSK_setup.exe

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:

91a82da992983d78672aea610fb9d055

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

 

The main improvement of MULTIPSK 4.43 is the following:

 

Ham P25 Phase 1 decoding (but not the voice)

 

"P25" is the acronym for "APCO Project 25", for two different radio systems: "Phase 1" (used also by Hams) and the most recent "Phase 2" (not used by Hams). Only the "Phase 1" P25 mode is decoded by Multipsk.

It is used in VHF and in UHF. It is a mode for professionals but also used by amateurs (according to a precise organization). For Hams, it is spread in a world net by using, among other means, repeaters and Internet.

 

The amateur P25 communications are the sole object of the Multipsk decoding (professional communications are decoded but ignored). The P25 is considered as a "professional" mode by Multipsk (but the Ham decoding is not limited in time).

 

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

Note: the voice communication decoding is excluded because it needs an IMBE Codec.

 

For Hams and SWL, the P25 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 P25 repeaters are located, with their frequencies, for each country: https://www.repeaterbook.com/repeaters/niche/index.php?mode=P-25

 

This mode is in freeware, so without time limitation.

 

See general specifications below.

 

 

Note about translation of Multipsk.exe and Clock .exe:  the 4.42 version of Multipsk has been translated to Spanish by Joachin (EA4ZB), from French.

See: http://f6cte.free.fr/Translation_files.htm.

 

73

Patrick

 

Description of the P25 mode

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

 

Modulation : each double logic signal (dibit) directly modulates, through a raised cosine filter (to reduce the bandwidth needed), the VHF or UHF frequency in 4FSK (on about +/- 4.5 KHz). So this signal is received in base band after FM demodulation.

It is also used a "CQPSK" modulation, which is demodulated as C4FM.

 

Reception mode: FM

 

Shape of pulse : raised cosine filter

 

Bandwidth : about 9 KHz

 

Detection and synchronization code: yes on 48 bits.

 

Codes: several codes are used (Hamming, BCH, Golay, Reed-Solomon...)

 

Interleaving : no

 

Scrambling: no

 

Transmission

 

Each "superframe" is composed of the following data units: Header / Logical link 1 / Logical link 2 / Logical link 1 / Logical link 2 / Terminator (with or without Link control).

 

Each data unit is composed of a unique frame synchronization word on 48 bits, followed by a network identifier on 64 bits giving among other information the data unit type, and finally a piece of information depending on the data unit. The lenght and the coding of each data unit are different. The main piece of information is, of course, the digitalized voice.

 

The pieces of information that interest Multipsk are the ones contained in the Logical link 1 unit and in the Terminator with Link control unit, because they carry the IDs (Source + Talk Group or Destination + Source).

 

Note: contrary to DMR, this is not a TDMA system as it is managed only one transmission.

 

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 http://f6cte.free.fr/DSTAR.ZIP file, but taking into account only the reception part (no P25 transmission by Multipsk).

 

 




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