On Oct 15, 2006, at 9:33 AM, Bill Turner wrote:
> If CW is digital, it then follows that dit-dah and dit-dit have the
> same numeric value and are therefore the same character.
From the channel encoding sense, amateur "CW" is a one-bit code (on
or off).
It is source encoding ("bit timing") that maps these two states (not
two bits, but one bit) into more states: viz, dit element, dash
element, inter-element spacing, inter-character spacing.
A further stage of source encoding maps a letter A into a dit
followed by and inter-element spacing followed by a dash, and
followed by an inter-character spacing.
When you send GG instead of "going" it is yet another level of source
encoding.
The "CW modem" that is used to match Morse to the HF channel is
simply one bit on-off keying of a single carrier.
With RTTY, the modem is FSK and it has two non-overlapping carriers.
Baudot is just a source encoder (so is ASCII). And when you type 73
for "best wishes" (or "73's" for "best wisheses") that is yet another
level of source encoding.
You can pass Baudot as a single on-off keyed carrier (as the early
amateurs did), but the use of two widely spaced carriers is a better
channel encoder ("modem") for the HF channel because FSK can counter
selective fading (just look at the behavior of the amplitudes of your
crossed ellipse display). Many software modems (and hardware modems
like the ST-8000) can be operated as Mark-only or Space-only and you
can see how much the use of two carriers bring to the table.
73
Chen, W7AY
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