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Posted by John Evans on 10/27/07 17:06
On Sat, 27 Oct 2007 01:45:25 -0700, "Green Xenon [Radium]"
<glucegen1@excite.com> wrote:
>Dave Platt wrote:
>
>> In article <46fc71d2$0$24285$4c368faf@roadrunner.com>,
>> Green Xenon [Radium] <glucegen1@excite.com> wrote:
>
>
>>>So there is no way to decrease how far the sidebands will go?
>
>
>> With FM? Nope, not in the way you're hoping. Modulate a carrier Fc
>> with a frequency Fm, and the first sidebands will be at Fc+Fm and
>> Fc-Fm, just as would be true with AM. That's the narrowest you can
>> get.
Oh dear - what about the deviation?
The rule of thumb bandwidth required for FM (Carson's Rule) says the
bandwidth is given by
2x(peak deviation x highest modulating frquency).
So a system with a maximum modulating sinusoidal frequency of 15khz
using a deviation of 75khz needs 180khz bandwidth minimum.
Note a pulse would require a far greater bandwidth.
http://www.fmsystems-inc.com/eng_fm.htm
http://en.wikipedia.org/wiki/Frequency_modulation
gives
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