[SOC] MCW, again. - channel occupation spark, arc and MCW

[g4jht]

1) The original spark Tx although, highly inefficient since the antenna 
was only energized around 4.5% of the time during each spark. The 
received  signal after envelope detection  in the basic crystal type 
receivers of the time produced a tone related to the spark frequency (I 
see references to 1000 sparks per second) in the  operators headphones.

3) The arc transmitter produced a continuous wave used a back wave shift 
keying technique with either radiated or with an "absorber circuit) as 
the arc could not be stopped once struck. But the resultant CW signal  
required  a BFO to convert it into something other than clicks in the 
operators headphones.

3) Although all coast stations were required to convert from spark (B 
waves) to CW (A waves) from 1935, ship stations could still use their 
spark set up to 1940. Many ships retained their spark sets as emergency 
transmitters during WWII, I understand. I am told the note from a spark 
set had a unique and very penetrating signal.

MCW may well have been introduced so the basic (TRF?) receivers in use 
on the ships fitted with  spark sets could resolve the signal from the 
coast  and stations using CW  tube transmitters.

On that basis while you could use a BFO with MCW; that was never the 
intention.

The  advantages of MCW  were and are,  that as I have written before it 
cuts through both static, and reduces QRM from CW signals. In areas of 
high traffic density permits use of lower frequency tone "rough note" 
signals by coast stations to cut through the "din" of 10 or more 
stations calling at once! There was a Spanish coast station that sounded 
like coffee grinder.  While the ability of weak MCW to penetrate 
tropical static may have contributed to any lives saved in the last 100 
years.

I have concluded that using a filter close to the width of the signal, 
helps resolve weak MCW signals as with all signals by enhances the S/N 
ratio, as will having the AF gain up and backing off the RF gain, 
presuming your signal if S5 or stronger (my noise is at S2 max).

The only set I know in common ham use that has MCW is the Ex British 
Army Tank Set : The WS19 and USN  AN/RC5

73, Dave G4JHT/EI0DB/VP8ART   West of Ireland. (2600 nautical miles East 
from NY) :-)