fish@ihu1g.UUCP (Bob Fishell) (01/25/84)
Well, folks, seems the ol' fish has got a few eggs on his face, but it ain't
the first time it's happened...
In my earlier response to a question about AM stereo, I implied that the
FCC had ruled on more than one AM stereo format, and that this would result
in a gaggle of competing, mutually incompatible systems for the manufacturers
to contend with. I was wrong. I think I had the AM stereo ruling confused
with something else, stereo sound for TV, I think. Anyway, I shall in the
future do a little research before shooting off my big, fat terminal.
The FCC did, in fact, approve only ONE of the AM stereo systems under
contention. This was the AM/PM system developed by Magnavox. The system
uses conventional amplitude modulation for the L+R (mono) matrix information.
The L-R component is broadcast by phase-modulating the carrier wave, with
a phase deflection of 1 radian (57.3*) corresponding to 100% modulation.
Amplitude modulation is kept to 95%, so that the phase information in the
CW is always detectable. In addition, a 5-Hz trigger signal is imposed
on the audio as a way of telling the receiver that an AM stereo broadcast
is being received. The system results in an overall signal degradation of
about 5dB, which is not too bad.
Other systems proposed to, and rejected by the FCC included Motorola's
C-quam "compatible quadrature" system, and an AM/FM system tested by RCA
as early as 1959. That it only took the FCC a little over 20 years to
approve an AM stereo system inclines me NOT to retract my statement about
that august agency's hind quarters.
The Magnavox system got the nod early in 1980, but the FCC ruled to delay
introduction of AM stereo broadcasts until early in 1981, so as to allow
manufacturers and retailers of audio equipment to adjust. Note, however, that
the arrival of AM stereo was not heralded with a blast of trumpets by
that industry, receiving practically no notice in the audio mags. I
guess that, although Magnavox stated they would license the system to
any interested manufacturer, it just hasn't caught on. Oh well, does the
nation NEED AM stereo? I doubt it. Most AM stations play such incredible
garbage that it doesn't deserve to be played through anything bigger
than a 2" speaker anyway. I may be wrong yet, but I think that AM stereo
will wind up on the ever-growing pile of audio Edsels that's been a
hallmark of the last 20 years or so in the industry.
Bob Fishellfish@ihu1g.UUCP (Bob Fishell) (01/26/84)
Hmmph! I just got a flame about my AM stereo article, posted earlier today,
whierin I stated that the FCC did, in fact, approve only one AM stereo
format. The flame said that apparently my first article was right -- there
are several (4, I think) AM stereo systems being used, not one.
I got my info from a 1980 issue of Popular Electronics (now Computers &
Electronics). The article announced that only the Magnavox AM/PM system
had been approved. I guess that PE and I were both wrong. Has anybody
else seen this article? It was the cover story on the issue; I still have
my copy, but I feel that my credibility has been compromised. Sigh.
Such is the Information Age.
Bob Fishellrfg@hound.UUCP (R.GRANTGES) (01/26/84)
I believe your information about the FCC is a little out of date. Actually they ultimately decided to let "the marketplace" decide, presumably in keeping with a recent president's ideas about hairy-chested free enterprise. In any event, four or five systems have been given the nod to compete. One recently gave up voluntarily. From time to time I see promises that someone is going to bring out a receiver for brand x. E.G., Delco, I think announced it would use the Motorola (?) system. Meanwhile there are some sets on the market that will decode all or most of the four versions. Sony recently announced a portable that received any of the four with but one switch for the listener to throw.Someone is marketing a transmitter that will transmit any of the competing systems with the right applique circuitry. In stereo TV, the last I saw an industry committee was rushing to make a recommendation to the FCC before the end of 1983. The hope was that the FCC might accept the recommendation of the committee rather than repeat the AM stereo fiasco. The report had to be ready by the end of the year because for some reason or other such a committee would become illegal after that (antitrust foolishness). Thus, it is possible, but unlikely, that by the end of "Big Brother year" we could have both AM and TV Stereo. By the way, if you are near an AM transmitter there is no reason it shouldn't sound pretty good. Maybe not as good as FM stereo, but definitely a plus for those who were listening anyway. -Dick Grantges hound!rfg