[BC] Re Oscopes Bessel Null and FM

[Mark Humphrey]

On 7/21/06, Xmitters at aol.com <Xmitters at aol.com> wrote:

> Then kick in a Carson's filter that limits the occupied bandwith according to
> his well known formula. I would be willing to bet a round of beers that the
> overmod flasher would either stop winking or it would not wink as often as it
> would without the Carson filter. It seems that the lopping off of those higher
> order sideband pairs (that last 2% of occupied bandwidth) would do two things.
> One would be to very slightly reduce the amplitude of the recovered audio at
> the receiver. The other would be that distortion products would be created.

This is an interesting question.  If the audio were "aggressively
processed", it would likely be clipped, thus having lots of odd-order
harmonics.  But wouldn't the Carson filter remove the sidebands that
represent the higher (harmonic) modulating frequencies -- which extend
farther from the carrier --  to a larger extent than the the sidebands
generated by lower (fundamental) fundamental frequencies?   If so, it
might act as a low-pass filter on the demodulated audio.

It's a well-known fact that the peak amplitude of a "square wave"
(clipped audio) increases if you attenuate the harmonics with a
low-pass filter. So the Carson filter might actually cause peak
deviation to increase -- or would it?

Mark