Re: [amsat-bb] Re: Looking for polynomials

[Bob Bruninga <bruninga@xxxxxxxxxxxxx>]

On Fri, 21 Jul 2000, Robert McGwier wrote:

> >FM transmitter.  The problem with AFSK is that you have to do TWO detections.
> >One to do the FM detection, and then another detection to on the audio to
> >get to data.  This is two harsh nonlinear processes, two threshold effects,
> >etc. etc. to deal with.    As a communications professional, let me assure
> >you without proof and make an argument from authority rather than technical
> >analysis,  AFSK SUX.

Yes, but in a given (fixed) FM voice Bandwidth (say 16 KHz) of an amateur
FM voice transceiver, I am beginning to realize that it is BETTER than FSK
at 1200 baud because of the "FM Improvement Effect" which actually can be
thought of as a "spreading" process to better utilize the existing
excessive bandwidth, and that wider AFSK signal can be received with
effectively a 4 to 1 "spreading gain" minus any dual-detection losses...

Or something like that...

At least for my test, the 1200 baud AFSK was 7 dB better than the 9600
baud FSK.  Again, an apples and oranges test, but at least a data point..

de WB4APR, Bob


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