[BC] Mono Expands on the FM Band

[Hershberger, Dave]

>   A old time engineer told me that the FCC made a major 
> mistake in choosing
> the GE/Zenith FM stereo system over the Murray Crosby system. 
>   The Murray
> Crosby system worked better and had much less hiss at low 
> signal levels but
> it was opposed by broadcasters because it interfered with 
> 67-Khz SCA music
> services which was a major revenue source for FM broadcasters 
> at the time.
> A short-sighted decision I think in retrospect.
> 
> -Nat
> 

I heard a bit of folklore a long time ago about how GE/Zenith was chosen
over Crosby.

Most people have heard of Occam's Razor. Well, the FM stereo system was
chosen by Harold Kassens' razor.

One day Harold Kassens (then a FCC staff engineer) brought in his electric
razor. He held it near the Zenith prototype FM stereo receiver and turned it
on. The Zenith receiver went, "bzzzzt!" Then he held it near the Crosby
receiver and turned it on. The Crosby receiver went, "BBBRRRRRRZZZZZTTTT!!!"
(Much louder QRN than with the Zenith.)

Crosby protested that this wasn't a fair test, because the prototype
receiver used a slope detector for L-R, and as such, it was much more
susceptible to impulse noise. Crosby correctly pointed out that this was not
a system problem, but rather an implementation problem that could be and
would be solved. If he had time to replace the slope detector with a "real"
FM detector, the impulse noise problem would go away.

Harold Kassens was not persuaded. So Kassen's razor tilted the odds in favor
of GE/Zenith.

Crosby did have better stereo S/N, but as others have pointed out, it was at
a cost of mono loudness and fringe and multipath effects that would cause
noise bursts and distortion as the L-R subcarrier dropped below threshold.

L-R on a linear VSB or USB subcarrier at 19 kHz would be a much better match
to the triangular noise spectrum of FM.

Dave Hershberger 
Principal Engineer 
AXCERA
Tel: 530-272-HDTV (4388)
Fax: 530-272-4505 
dhershberger at axcera.com <mailto:dhershberger at axcera.com> 
AXCERA. Axcessing the new era of digital communications. www.axcera.com 
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