23 April 2015

Arcotel MAHRS-2400 ALE burst (Telefunken Racoms)

Fast bursts sent every 500 msec, spreading about a 2800 Hz bandwidth. Each burst shows a short preamble of 8 un-modulated carriers, symmetrical with respect to the center frequency of the signal, and a short PSK-2 preamble. The data segment is a serial tone carrier at ~ 1800 Hz with a PSK-8 manipulation at 2400 baud.


The MAHRS protocol, or better the procedure, was described in WUN-10 newsletter, and here reported:
"For establishing the link between two stations there is a call of one dot each second at a length of 500ms. Most of the time the station calls 62 times then changes back to listening for 60 seconds and then selects a new frequency for calling. The selection of freqs happens according to position of both sender and receiver, actual daytime and actual sunspot numbers. The system calculates a prediction model of propagation and decides which line may be the best. When in contact the called station answers after waiting a maximum of 15 seconds by one dot of 500ms and the both stations give their "handshakes" and then the full transmission starts using a high speed ARQ like transmission system at a speed of 4800 bps" [http://www.udxf.nl/WUN-v10.pdf]

Sometimes you find the MAHRS protocol reported along with the names EADS/RADCOM and Arcotel: the former is the name of the HW producer, TELEFUNKEN Radio Communication Systems - TELEFUNKEN RACOMS (http://www.army-guide.com/eng/firm3787.html) while the latter (Arcotel) is the name of the modem (now indicating the radio processor).
The source should be the German Mil, as reported in the above link to WUN newsletter http://www.udxf.nl/WUN-v10.pdf

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