What has become of it? I remember that once upon a time almost all US made rental cars had AM-Stereo receivers. Lately my rentals were all Japanese and none of them had it. IIRC even a Saturn L300 I rented a couple years ago didn't. The home stereo we bought about five years ago doesn't either. AFAIR it was designed by the US company SonicBlue. It has all the other bells and whistles so AM-Stereo must have been pretty low on the feature pecking order. Or is it gone already?
Every station around here pulled the plug years ago. Minor problems with the transmitter caused it to act up, but still allowed them to operate in mono with no problems. Budgets are tight, so when they got few, or no complaints, they didn't bother to turn the encoders back on.
I was giving a descriptive explanation of what i meant, not a recommended implementation. The recommended implementation does not use DFTs, and is a FIR implementation.
Encoders? I thought stereo AM required a second transmitter for L-R.
C-QAM, all on the original carrier.
That is for HDTV, one for the analog channel, and one for the digital channel. ;-)
Seriously, I remember when WLS-AM (Chicago) went stereo. They were talking about how they had to reduce the power from one transmitter when they brought the second on-line. There were other issues as well, but it's been a long time though.
In case the OP (or others) are interested, I happened to come across an article with the original phase quadrature network in it (I posted a scan of the relevant page in a.b.s.e) in a tutorial article in Elektor in
1977.The unusually wide bandwidth of 30Hz to 16kHz is because this network is designed to provide the quadrature for an Ambisonic surround sound coder/decoder rather than SSB.
Performance appears to be pretty good for the number of opamps used.
Regards Ian
They may have had to reduce power because the transmitter couldn't meet specs in stereo mode when they ran it at full power. Some transmitters generated serious amounts of spurs and harmonics when converted to stereo. A lot of AM stations have a second, or even third transmitter for day/ night power levels, and emergency operations. Its cheaper to use a timer to switch transmitters than to keep a full time engineer at the station to make the adjustments when the power and antenna patterns change for night time service.
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