11 June 2016

Arcotel MAHRS-2400 serial (Telefunken Racoms)


This signal has been heard several times, this one on 12282.5 KHz on USB at 1430z. An old WUN publication (http://www.udxf.nl/WUN-v10.pdf) and some other logs report the 12282.0 and 12282.4 frequencies as operated by German Military, so probably the 12282.5 frequency is also owned by that same network.
MAHRS-2400 is a STANAG4285-like 2400Bd PSK-8 serial waveform (pic. 1) with 2 x 8 pre-tones which are simmetrical in respect of the 1800Hz carrier

pic. 1
The signal exhibits ACF of 106.66ms or 256 symbols due to its frame structure: 80 symbols length probe (kown symbols) followed by 176 symbols of data (pic. 2)

pic. 2
The evidence of a pronounced 2-ary states in the constellation suggests that the known-data probe are modulated using BPSK and then scrambled to appair as 8-ary in air. The BPSK probes are clearly visible in pic. 3 after after increasing the FFT size.

pic. 3
The waveform is similar to the one used in the MAHRS ALE mode, a 500ms burst system briefly reported here

This signal is linkable to the HRA 5100 radio communication system used in airborne platforms (hra-5100.html). As far as is recoverable in the web, "MAHRS" is the name of the HF radio-data standard used for data transmission while "Arcotel" was originally used to indicate the modem:  recent Telefunken Racoms HF transceivers have integrated radio processor and modem, Arcotel is supposed to indicate just the radio processor. The company's name "Telefunken Racoms"  is used since 2004 (http://www.army-guide.com/eng/firm3787.html).

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