17 May 2017

RACAL MA4248 "MEROD", ARQ FSK 266.6Bd/800Hz


The transmission was heard on 9274.0 (cf) and consists of FSK-2 bursts with shift of 800Hz and manipulation speed of 266.67 Baud. Thes features points at the RACAL MA4248 device, also known as MEROD (Message Entry Read Out Device): thanks to my friend KarapuZ for the help in identification.

Fig. 1 - manipulation speed
Fig. 2 - FSK shift
Once demodulated the signal, the measured period is 48 bits:

Fig. 3 - 48-bit period
The RACAL MEROD transmissions can be decoded by Code-300, although the contents are encrypted: 

Fig. 4 - MEROD RAC-ARQ mode running in Code-300

The RACAL MA4248 "MEROD" device was  designed for sending messages in burst transmission mode over HF/VHF/UHF radio links and were therefore used by special forces in combination with a man pack radio, these unit is also known as a tactical data entry device, TDED. MA4248 utilise a complex error correction system that ensures that the message can be correctly received over very poor quality HF links. 

Fig. 5 - RACAL MA4248 device


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