On 6/15/2013 11:23 AM, Vic, K2VCO wrote:
> I wish people would stop using the term 'MCW' for the method of
> producing CW by feeding a (one hopes) clean audio tone to an SSB
> transmitter.
Feeding an audio tone into the mic input of an SSB transmitter is
*most certainly* MCW if the tone is not absolutely clean - no
clipping, no distortion, no hum, no extraneous audio - the SSB
transmitter carrier suppression (carrier balance) is not at least
40 dB, the opposite sideband suppression is not at least 60 dB
and there is no clipping or compression in the transceiver IF
stages or final amplifier.
Without proper carrier suppression, opposite sideband suppression
and distortion free tones, the resulting signal will be twice the
highest distortion product wide *at least* and potentially wider
if the IF stages or final amplifier is non-linear because of the
generation of *additional* IMD products.
MCW was used in past years for maritime communication because it can
be received by a receiver without a BFO and there is no 'zero beat'
phenomenon which could cause a listener to miss a signal.
Modern "MCW" is a single sideband system (one sideband with a reduced
"carrier") where the carrier level is only high enough for reliable
demodulation and the keyed signal is generated separately not using
using a modulation process.
Tone keyed CW as practiced by many amateurs today and generated by
common software is a garbage generating mess and those who engage
in it on any frequency below 145 MHz should be tarred and feathered.
73,
... Joe, W4TV
On 6/15/2013 11:23 AM, Vic, K2VCO wrote:
I wish people would stop using the term 'MCW' for the method of
producing CW by feeding a (one hopes) clean audio tone to an SSB
transmitter. This is a way of generating CW -- which may or may not be
the best way -- but it is not MCW.
MCW as it has always been understood is a carrier modulated at an audio
frequency -- an AM signal. The signal is keyed on and off to transmit
Morse information, but it has two sidebands on either side of a carrier.
If the tone is, say, 600 Hz, then the signal will be at least 1200 kHz
wide. It is illegal in our HF CW bands.
MCW was used in past years for maritime communication because it can be
received by a receiver without a BFO and there is no 'zero beat'
phenomenon which could cause a listener to miss a signal.
On 6/15/13 3:40 AM, David Woolley (E.L) wrote:
Most modern commercial transceivers effectively generate CW as SSS
MCW. I think the K3 does it at about 15kHz or less, which is within
the audio range. I suppose the K3X could generate it directly, by
just keying the I signal to the modulator; however, that would mean
moving the VFO between transmit and receive, at the QSK rate. (Keying
I on the K3 would probably be a bad idea, as it would mean that any
transmit roofing filter would need to pass the first LO frequency and
therefore be subject to some carrier leak when key up, so I presume
that the CW is actually synthesized as fully fledged MCW. Even if it
keyed I, you could treat that as MCW with a side tone of 15kHz.)
Even the K2 architecture is effectively an MCW one, but in that case
the initial tone is in the MHz range.
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