[BC] Re: FM Modulation, the O'scope and Bessel functions.

[Paul Christensen]

> Correct me if i'm wrong, but high order sidebands
> that don't make it through the receiver's IF could add to the modulation
> percentage, right? Especially those little short duration spikes that 
> light the
> overmod flasher.

If the higher-order sidebands are a result of excessive carrier deviation --  
one component of FM bandwidth.  As a rough approximation, Carson's Rule 
states that ~ 98% of occupied bandwidth can be determined by use of the 
following formula:

BW  =  2(Dmax + Fmax)

Perhaps it's for the reason you mention that the FCC interprets 
over-modulation as exceeding one peak per ten-second interval, or six peaks 
per minute.  This allows for a relatively generous margin of error whether 
the error is truly in the transmission, or in the measurement.

Paul


====================================
Paul Christensen, CPBE, CBNT
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