Text 45257, 71 rader
Skriven 2006-12-29 00:25:00 av Michiel van der Vlist (2:280/5555)
  Kommentar till text 45130 av Roy Witt (1:397/22)
Ärende: AM Stereo Radio                     was: America
========================================================
Hello Roy!

On Wednesday December 27 2006 14:20, you wrote to me:

 RW> The AM stereo system in use was the Motorola C-QUAM system. Wikipedia
 RW> has a breakdown of the four systems in use then and the emerging
 RW> winner was the Motorola system, which was eventually santioned by the
 RW> FCC as 'the' system to use. As a Physics mathematician, you should be
 RW> able to understand the formula used to modulate the system as they
 RW> explain it, better than I could explain it.

Qudrature Amplitude Modulation. What it boils down is that the carrie is
modulated in Am by the one signal and modulated in fase by the other signal.
The same modualtion type is used in colour TV for modulating the two remaining
chroma signals on the colour subcarrier.

For backwards compatibility with mono AM, the signals are rtotated 45 degrees
in the verctor plane, so that the AM signal is Left + Right and the fase
modulated signal is Left - Right.

 RW> You can hear AM stereo on 864khz from France Bleu out of Paris. It's a
 RW> 300,000 watt station, so you shouldn't have a problem picking it up in
 RW> Holland.

I am not in Holland, but I can receive it anyway. Indeed, there is a French
station there. There is nothing that indicates it is stereo. As one can expect,
that is the whole idea of making it downward compatible with mono receivers.

[..]

 MvdV>>> Probably because it required a special receiver to enjoy the
 MvdV>>> stereo. Which was not or not widely available....

 RW>> That's the rub. It didn't require anything more than what you
 RW>> already had to receive the station in stereo.

Enjoying the stereo requires a receiver capable of detecting the QAM signal. A
receiver with only an AM detector will NOT give you stereo. No way. The AM
detector in the receiver has only one audio output.

 RW>>>> * They put two transmitters online within their alloted
 RW>>>> bandwidth, one xmitting on the upper sideband and the other on
 RW>>>> the lower sideband. Tune your AM radio to center frequency and
 RW>>>> you got a broadcast in stereo without the hetrodyne of the two
 RW>>>> carriers.

 MvdV>>> With an oridinary AM radio, you would not have stereo...

 RW>> You would if the xmitter was capable of modulating the sidebands
 RW>> seperately. I don't know exactly how they did it, but I do
 RW>> remember hearing stereo reception on my AM car radio.

Are you sure that car radio did not have C-QUAM capability without you being
aware of it? That happens you know, that equipment has features unknown to the
user...

Over here AM stereo, or perhaps Medium Wave stereo would be a better term,
never made it. I have never seen a receiver for it offered on the market. Also
I do not recall ever having seen an experimental receiver in one of the popular
radio magazines. From what I gather it must not be all that difficult to design
an add-on for an existing AM/FM receiver capable of FM stereo, but I never saw
it.

The French station on 864 you mentioned is the only one I ever heard of here
that supposedly transmits on stereo in the Medium wave band.


Cheers, Michiel

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