[BC] AM Carriers

[Richard Fry]

RF wrote:
>>other than for Morse code, a carrier really serves no purpose toward
>> conveying information.  As examples:  the L-R FM stereo signal is
>> transmitted with no carrier, and so are the chrominance portions
>> of NTSC & PAL color television.

Larry Bloomfield replied:
>That certainly is a much different way of looking at it than I've ever
>heard before. Perhaps you can explain what is meant by sub-carrier or
>doesn't that exist either. :-)  I think you may have really stirred up a
>hornets nest here. Think I'll sit back and watch the action on this list.
_______________

A (sub)carrier is used when generating the AM sidebands of the L-R and color 
signals, but the (sub)carrier itself is suppressed from the output waveform. 
Only the sidebands are there.

Proof of that is seen by observing the composite baseband spectrum of either 
signal when the L-R or chrominance input waveform to the encoder is zero. 
This occurs for stereo FM when L=R (i.e., monaural), and for color 
television when there is no color in the scene (i.e., monochrome video).  In 
both cases, there is no subcarrier signal present in the composite spectrum 
except for the pilot carriers needed to sync up the receiver 
demodulators--and that carries no "intelligence."

RF