On going very interesting discussion: RF/IF vs audio.
> Well, I think you guys are both right.
>
> The DSP operates ahead of the audio stage, and thus can
> be called IF.
>
> Of course, the frequency of 14 khz is certainly in the
> audio range.
Well, do you understand the difference between these two
words: acoustic and electromagnetic?? If one signal
is acoustic and the other electromagnetic, do we think
of them being "the same"..........no, of course not.
Maybe you might have heard of the "Andersen Alternator".
This was a machine which generated thousands of watts
of RF energy.....at 17 kHz! It was real RF, not audio or
acoustic energy!! And it covered oceans for all the ships
at sea.
An audio signal is always referenced to DC; just as is
a video signal, as in television. TV rcvrs have DC
restoration circuits to be sure the anchor to DC is
present.....otherwise the picture can appear "washed out".
The "intelligence" in an audio signal is always present in
the lower frequency ranges, 200 to 3 kHz or so --- not up
at 14 kHz!! Yes, an orchestra which happens to have
triangles or cymbals will radiate acoustic energy up to
15 kHz as compressions/rarefactions of the air to propagate
the sound to the ears of the listeners; but the percussion
section keeps it all referenced to "DC".
However, the intelligence in an IF 14 kHz signal is all
centered about the 14 kHz "carrier". And to access that
intelligence, it must be converted to "baseband"...see
a previous post on that topic.
Just as with the Andersen Alternator, no one about the
transmitting station, nor anywhere near the gigantic
antenna towers could actually "hear" with their ears
the "intelligence" of the signal.....it was electromagnetic,
not acoustic. It was propagated at the speed of light,
not at 1100 feet per second, the rate of acoustic
travel in the usual atmosphere of our homes/offices.
Anyway, just some more thoughts on the topic....
73, Jim KH7M
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