On Tue, 22 Jul 2008 10:49:27 -0400, Jerry Flanders wrote:
>Shifting a constant carrier back and forth does not require linearity
>in later stages - for the same reason that CW does not.
Then, at 12:06 PM 7/22/2008, Jim Brown wrote:Hmmm. Well, yes and no.
Shifting a carrier in frequency results in
switching transients (clicks).
The transition time constant has to be reasonable, of course, just as
CW keying on/off transitions are smoothed to reduce click levels.
This is all taken care of (hopefully) in the rig design. It is not a
consideration for an appliance operator, which most of us are these days.
Back when guys were modding their rigs to add FSK to them (and some
did, 30-40 years ago) this might have been a problem. The early AFSK
units had problems, too, if the tone transitions were made without
regard to phase. It was a big deal to get a phase-continuous
transition in the early/mid 70's, IIRC.
Unless an operator can do some tests on his sigs to verify quality he
is generally better off using FSK for the sake of band crud reduction.
Jerry W4UK
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