The Multiple Adaptive HF Radio System (MAHRS) is based on the Arcotel transmission processor that controls the automatic frequency selection, the link establishment and the following waveform for the ARQ-based exchange of data. The modem used is the Echotel 1810 manufactured by EADS RACOM.
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 "procedure" was described in WUN-10 newsletter, and here reported:
The MAHRS "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]
