Re: X-Band Fidelity

[Bob Smith <rmsmith@ma.ultranet.com>]

Dan Strassberg wrote:
>
> As far as I know, from a technical standpoint, that's a total crock. Based
> on his completely subjective observations (ALL observations of sound quality
> are subjective), Shel noticed an effect that didn't exist. He called the
> WMEX CE and got a satisfying explanation. The CE must have thought to
> himself "what possible downside could there be from telling this guy what he
> wants to hear?"
> 
> I daresay that until the carrier frequency approaches maybe three times the
> audio bandwidth (that's the bandwidth of the audio chain in the receiver,
> which, on AM, is usually less than the transmitted bandwidth), you would not
> notice any effect of the carrier frequency on the audio quality.
>

Dan:

	While your analysis is correct in math it isn't correct in the real
world.  The higher frequency stations frequently sound better than the
lower frequencys.  This is more than subjective, and is particularly
true of AM directionals.
	The AM antenna impedance varies with frequency, and of course so does
the reactance of the components used to match the tower to the
transmission line and transmitter.  When you do the math and calculate
the impedances presented to the transmitter final amplifier at the
sidebands it can get pretty ugly.  The higher you go on the band the
smaller percentage change in frequency results from sweeping up and down
10 kHz.  This results in a less unbalanced load to the final and better
sideband transmission.
	So, it isn't a crock, its a fact!


Bob Smith

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