FM Quad Demodulator
An information for Quadraphonic collectors written by Klaus Hoenemann with kind support of Nick Perugini, Aug. 2014
In this article, I’ll describe a one of a kind of item, an outboard FM Quad demodulator adapter. This is the unit many quad receivers have the FM Multiplex output jack for. As you know having been around in the era, the endless news was that any day now the FCC will approve FM Quad in the United States and that would make Quad mainstream, which unfortunately never happened.
In the world, there were different ideas to transmit quadraphonic broadcasts via FM. Great Britain planned a special matrix system (Matrix H) and in the Netherlands, a matrix-encoded quadraphonic system was used to send some listening stories. Elsewhere the transmission stations experimented with discrete systems in which the signals were not mixed. However, discrete transmission would have required a complete restructuring of the entire broadcasting technology.
Some stations did test broadcasts by sending the quadraphonic program simultaneously via two regular stereo stations. Therefore, you had to combine two home stereos, one for the front and another for the rear. The Swiss Station DRS sent some of those transmissions on its programs DRS 1 + 2.
All parties realized that this could not be a permanent solution. They only wanted to test the interest of the audience, which was highly enthusiastic by the way.
Left side: Swiss Radio Station Commercial Poster.
I was aware that various manufacturers who supported CD-4 made modifications to their receivers for testing the FM Quad system, so that in demonstrations they could receive test broadcasts in quad. JVC, Technics, even Sansui made a few QRX-9001 and 999s with built in quad FM demodulators, but I never saw or heard of outboard ones being made. This unit has a sticker on the bottom, "connect to RE-8420" which if you Google that model number you'll find it was an all in one quad receiver, probably came with four fairly cheap speakers, and had a built in Q8 deck. I'm assuming they (Panasonic) loaned the entire setup to people in the FM Quad test area, to receive and evaluate the broadcasts.
The Panasonic RD9610 uses a system developed by Lou Dorren, our famous "CD-4 veteran". When connected to a quad receiver (QRX-7001) FM MPX out jack, and the signal fed back in via the tape monitor loop, you use the Sansui tuner but this demodulator is actually doing all the work beyond basic tuning to the station. This demodulator is receiving the raw FM signal and then decoding it to regular FM stereo since there is no quad signal to receive. It plays double stereo that way, the same program in both front and back, like most CD-4 demodulators do when playing a stereo LP. With a mono FM station its 4 channel mono, all outputs are on. It has interstation muting, and when it comes out of muting as you first tune to a FM Stereo station, it assumes it to be Quad, so the FM 4-Channel indicator lights up in green and all 4 corner red lights light. The unit then analyzes the signal and finds no quad carrier, so it switches to double stereo and the FM Quad light goes out, along with the rear red light. It sounds identical to the 7001's internal FM stereo, by switching between tape monitor and FM there is no difference in sound or performance between the Panasonic Quad FM demodulator receiving the FM and the Sansui handling the FM signal normally.
left picture: Receiving a stereo station
right picture: The operation and the circuit design are strongly reminiscent of the CD4-technology.
All four lamps illumate when first tuned to a stereo station. The unit is figuring out if the station is broadcasting in Quad or Stereo. The unit starts in Quad, assuming the station is in Quad, then switches to stereo when no Quad signal is received after a few seconds delay without output muted.
Thanks to Nick Perugini for sharing the pictures and information about this unit. It may be the only one in existence. In handwritten Japanese inside it says it’s “prototype #2”.