[CW] MCW on 500 khz

[D.J.J. Ring, Jr.]

Some coastal radio stations like ITT Mackay New York City WSF ran MCW on
their working frequency but they were very few in number became MCW was
very broad about 2 kHz wide if you include harmonics.

A2 MCW was kept to keep compatability with Type B emission, Spark. Old auto
alarms originally only responded to modulation and would be triggered by
the modulation of a spark signal but not an ICW or an Interrupted (that is
"keyed") Continous Wave signal. Later autoalarms responded to MCW and CW
signals.

Some ships had crystal radio receivers with fixed tuning for 500 kHz used
as yet another backup receiver for use in an emergency. These receivers
only received Spark and Modulated Continuous Wave MCW or IMCW Interrupted
Modulated Continuous Wave (A2) signals.

73

David Ring N1EA

On Sun, Sep 21, 2025, 10:12 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
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