I don't understand how you can come to that conclusion. Somebody else above in the thread said he thought the ST97 was a combination of switcher and matrix. I had looked at it before (350 tuner), and had determined that it was a switcher, but I wasn't certain. I have looked at the Scott schematic and since there is no accompanying block diagram or explanation of how the circuit works, it is difficult to analyze. There is no ring demodulator in the Scott, but two bridge type rectifiers perhaps achieving the same thing?
But, as discussed above in other postings, it seems the Scott 340 receiver along with the 350 series tuners used matrix decoding? at least that is what was presented earlier in the thread by another poster. I am certainly willing to be corrected about Fisher inventing the "chopper", or sampling method of decoding, as I could find very little data about it. Sounds like a great book, I ordered one from Amazon. And whatever type of decoder you're using, in broadcasted FM the upper frequency limit of the recovered audio signal is about 15 KHz (slightly less than half the sampling frequency).
(most high quality decoders used and still use this method)Īnd regarding the supposed " detrimental effect" of the signal being sampled at 38 KHz by the decoder, it has been already sampled (or "switched") at the encoding (transmitting) side : supressed subcarrier matrixing or (time-multiplex)switching are just two different mathematical ways to describe the same process but the transmitted composite signal remains the same. SCOTT heavily promoted his time-switchting method in their ads as being superior to other techniques, and it proved to be the case. its first commercial use in a stereo decoder can be found in the HH SCOTT 335, the very 1st MPX decoder available on the market and designed by SCOTT's chief engineer Daniel Von Recklingausen (incidentally also member of the FCC stereo multiplex comitee in charge of the evaluation of the various proposed encoding methods). (If you're into tube circuits try to get the 1st ed.)Īlso, in a historical perspective the switching (aka "time-division") mod/demod method was not pioneered by The FISHER and was already known (and used) in the 1950ies by the military for data/telemetry transmissions,etc.
A detailed description of this circuit can be found in " FM Multiplexing for Stereo" by Leonald Feldman (SAMS FMS-1, 1st ed, 1962, p.135), a book I would highly recommend to anyone interested by this topic. Regarding the circuit used in the EICO ST-97 decoder (and his stand-alone brother, the MX-99) it must be noted that it neither used a matrix nor a switching type, but a clever and unusual combination of both. I feel some small corrections/additions are in order:
Thanks to the O.P for this very interesting thread.