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Can audio be "side banded" to a higher Mhz signal?

Posted on 2007-04-10
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Hi Everyone:

      A friend of mine mentioned some theoretical ideas about audio.  One point he made which I did not understand is as follows:  He says that audio can be "side banded" to a higher Mhz signal.  I am not sure exactly what this means.

       Since this question is more theoretical as opposed to practical, I certainly welcome all shared thoughts or opinions regarding this question.

        I look forward to hearing from everyone.  

       Thank you.

       George
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Question by:GMartin
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Accepted Solution

by:
nobus earned 2000 total points
ID: 18881019
the term side band comes from radio transmissions (or even TV). you have a carrier wave frequency in the center, and the signal(s) are modulated onto it.
without special measures, this creates side bands at each side (lower and higher one) like this :
                                   carrier in centre
                   ____   |  _____
                  /         \ | /         \
-------------------------------------------------------->frequency axis
you can have emissions with SSB (single side band) which cut off the lower, or higher side band.
if you need more info; please ask - or was the question in another context ?
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Author Comment

by:GMartin
ID: 18883815
Hi There:

       Your description matches the context in which the term is being mentioned.  If you don't mind, I would like to carry this a step further.  For instance, in what practical aspect would "side band" be used like in radio or tv?  

        Thank you.

        George
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LVL 92

Assisted Solution

by:nobus
nobus earned 2000 total points
ID: 18887807
the size of the side band(s) determine the bandwith the emittor will take up in the frequency scale (see for analog TV : the side band is 4.5 MHz wide, so the total with is about 5 Mhz, for sound, the bandwith is max 20 KHZ (audio spectrum), so the bandwith can be much more limited here; and there is another one : telephony, where the bandwith is limited to 3 KHZ (so it is well understandable, but we do not need the higher frequencies)
now in radio, you have the Long, Middle and Short wave emitters; + FM
FM range - 88 - 108 MHZ ==>20 Mhz
AM range - 530 kHz to 1700 kHz  --> 1200 KHz = 1.2 MHZ
as you can see, the AM range is much smaller, but since the bandwith used is abouit 50 KHZ (Double Side Band), you can use for a given area 1200 / 50 = 24 stations , without interference or overlapping, and since the distance covered with this emittors rarely exceeds 100 KM, you can use the same scale again, further in the country

There is really much more to tell; here some more info :
http://en.wikipedia.org/wiki/Radio
http://en.wikipedia.org/wiki/FM_radio
http://electronics.howstuffworks.com/radio-spectrum1.htm
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Author Comment

by:GMartin
ID: 18901922
Hi There:

         Thank you so much for your prompt replies to this post.  I enjoyed going over the information presented which helped to put all of this in perspective.

         Many thanks again.

        George
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LVL 92

Expert Comment

by:nobus
ID: 18903776
well, i was in radio techniques for some time, so i know quite a lot about those - if you have anymore Q's - just ask George !
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