[CW] MCW on 500 khz

[Radio KH6O]

I'll add my 2 cents: Suppose I'm transmitting on 500 kHz with a modulated
800 Hz tone. Suppose you have your receiver's BFO set so that a signal on
500 will have a 600 Hz tone. The 800 and 600 Hz notes will create many,
many harmonics -- a very wide-band signal on either side of 500. The sound
is so distinctive that a radio operator, busy with something else, will
immediately get a shot of adrenaline through his system!

If you have a piano handy, try sending Morse with your arm pressing a dozen
keys simultaneously. That's what an A-2 transmission would sound like.

ITU regulations stated that all distress transmissions on 500 kHz were to
be  conducted with A-2 modulated CW.

In US Coast Guard Radioman School, we were told that some 500 kHz Auto
Alarm receivers would only respond to A-2 transmissions. (A ship in
distress will send an Auto Alarm, a series of 12 four-second dashes, prior
to sending the SOS transmission. Those 12 four-second dashes will activate
alarm bells on other ships within receiving range.)

Good stuff!

73,
Jeff KH6O and former USCG CW operator at Communications Station Honolulu,
NMO, 1977-1980



On Sun, Sep 21, 2025 at 7:12 PM Stephen Hayward via CW <cw at mailman.qth.net>
wrote:

> Greetings David,
>
> I always wondered why MCW was only used on 500 khz and not on other
> frequencies.
>
> Please advise.
>
> Many thanks,
>
> Steve Hayward
>
> Please advise why MCW was preferred over
> ______________________________________________________________
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/cw/attachments/20250922/128ed2e9/attachment.html>