Hi Todd
Of course, your wasted-power argument applies even more to AM than
suppressed-carrier DSB. But unless you're battery dependent, that doesn't
matter that much. A nice old boat anchor pumping wasted watts into the
atmosphere at least helps keep the shack warm on a cold winter night.
Yes... true! But the topic was DSB not AM or a comparison of every other
possible mode and how efficient it is and various other advantages and
disadvantages... Yes AM is inefficient and takes too much bandwidth. The
advantage of AM is that non-technical non-ham people can tune it easily,
hence the suitability for broadcast applications, whereas with SSB we
amateurs have to tune accurately to avoid making our QSO correspondent
sound like Donald Duck.
But at least, an AM station can work another AM station! I think DSB is
alone (as far as I can think of) in being the only mode where you can't
work another station using the same mode! Therefore it isn't just
inefficient and interfering, but also inconsistent [if widely adopted]. Too
many unpleasant negative "in"'s hi hi.
Steve WB6TNL... additional to what Allison said... if the two DSB stations
are perfectly aligned then cancellation will occur; if they are a few Hz
off, then what this will mean is, each FT8 tone will be ghosted those few
Hz away, at the same amplitude, by its equal and opposite counterpart from
the unwanted sideband. Faced with TWO tones to decode this will seriously
confuse the FT8 decoder. You might be able to get away with it if the
difference is small (a Hz, for example) but then that will probably mess
things up due to partial cancellation; and if the difference is more than a
few Hz then the FT8 decoder would detect and decode two equal tones where
it is only expecting one. Result: no decode, or at the very least, greatly
reduced probability of decode.
73 Hans G0UPL
