[SOC] MCW and Auto Alarm for MF distress

[g4jht]

MCW was specifically required on 500 Kc/s 600 meters for the auto-alarm 
signal of 4 dashes 4 seconds long with one second space (although the 
operator was required to sent 12 dashes.
The Auto-Alarm receiver was a 3 stage TRF set with a 16 Kc/s band pass 
centered on 500 Kc/s, with AGC and protection circuitry intended to 
prevent a continuous CW signal blocking out the MCW dashes. Early 
versions had an electromechanical Heath-Robinson gadget of relays 
rotating clutches and cams termed a "Selector" that timed the sequence 
of four dashes correctly spaced and then closed the bell circuit.
By the mid 70s the same functionality was provided by a single discreet 
TTL logic on a single 9 inch x 7 inch plug "Selector" PCB.

For anyone interested in spark, arc or early tube transmitters the 
(British) Admiralty Handbook of Wireless Telegraph 1931 or 1925 (some 
times turn up on book sites) are the books. lots of pictures of early Tx 
tubes.

73,
    Dave G4JHt/EI0DB/VP8ART :-)