In the marine CW service in the late 50's, nearly all traffic on the
Holy Wavelength [600m] was MCW. After all, it was the worldwide
distress channel. A lot on working frequencies was too. Unlike MCW on
the VHF ham bands, the RF carrier was also keyed, but in either case, it
was double-sideband amplitude modulation.
Shipboard transmitters usually employed motor-generator sets to get the
high voltages necessary from the ship's DC mains. They weren't filtered
well and most transmitters afloat were modulated by M-G whine. The M-G
sets also weren't well regulated so the voltages rose and fell with the
CW. The result, if you listened with the BFO on, was a chirping carrier
modulated by a chirping audio tone with a chirping whine in the
background. It was "distinctive" as Ron says but generally less than
harmonious. :-)
None of this MCW drivel has anything to do with the CW scheme for SSB
transmitters, pioneered if not invented by Collins in their KWM2 and
S-line equipment. It worked for Collins because their mechanical filter
suppressed the opposite sideband by something like 70-80dB, the balanced
modulator had good carrier suppression and the filter added to that, and
they generated a very clean sine wave.
73,
Fred K6DGW
- Northern California Contest Club
- CU in the 2013 Cal QSO Party 5-6 Oct 2013
- www.cqp.org
On 6/15/2013 10:04 AM, Ron D'Eau Claire wrote:
Quite right Vic. A.M. MCW was *required" for any emergency maritime
communications. Up until well after WWII, some ships still had crystal
detectors as the 'emergency' receiver should the main receiver fail. In any
case, A.M. MCW received on a superhet produced a very distinctive sound that
made it stand out from other traffic and was required or any shipboard CW
transmitter.
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