Late 50s philco curb find

[JGlenn]

I did a little searching and it was actually a primitive pay tv service in that started in the 50s and never really caught on. I guess there would be a box that got some signal over the air and then some aditional signals over a phone line to unscramble. kinda interesting.

[wa2ise]

Originally Posted by JGlenn

I did a little searching and it was actually a primitive pay tv service in that started in the 50s and never really caught on. I guess there would be a box that got some signal over the air

There were those supressed horizontal sync scrambled TV stations, usually up at the upper end of the UHF TV band. We had one in the NYC area on channel 68, here's the box you rented from the service


The missing horiz sync signal was added to the audio subcarrier, along with the soundtrack modulated as a double sideband suppressed AM carrier at around 31KHz (twice the horiz frequency), a lot like FM stereo is done where the soundtrack would be the L-R signal, and a "barker" (someone telling how great the movie service is) sound on the baseband mono audio, to be heard by people tuning the channel without the decoder on their TV sets. Then the box would add the missing horiz sync back to the video, and send that to the TV set. You'd see tons of pirate decoder boxes at swap meets and such, most not working all that well.

Building such a decoder box using tube technology would be rather expensive, similar to a TV set but without the CRT and deflection circuits. That's probably why it bombed, that much investment would have to be paid off in a couple of years and then getting movies that just finished their runs in movie houses but before they hit regular TV would be expensive too. "Wometco Home Theatre" lasted about 12 years before it folded.

[jr_tech]

Slightly different more primitive system which would not work for color:

"The Phonevision system was operational on station WHCT in Hartford, Connecticut for at least two years, ending in 1969. The station would run conventional (non-subscription) programming during the day as an "independent," and then switch to Phonevision encoded programming in the evening. The system operated by switching a delay line in and out of the video, which chopped the picture into slats (like looking through an open venetian blind). Half of the slats would be shifted to the right by a significant amount. Decoding reversed the process and slid the other slats over the same amount, realigning the picture. The video information was also reversed in phase, exchanging black and white. The audio was processed by "frequency inversion scrambling," shifting the audio spectrum up 2.625 kHz in frequency. This produced audio that sounded much like single sideband radio except that only high frequencies were present. Decoding of the audio was done by a dual-conversion processor. The audio was first shifted up 31.5 kHz, and then shifted down 34.125 kHz, producing a net "downshift" of 2.625 kHz. 31.5 was double the horizontal sweep frequency of 15.750 kHz, and 34.125 kHz was 13/6 ths of 15.750, giving a convenient frequency reference. The frequency tolerance was so tight that if encoded audio were recorded during a Phonevision broadcast, and then played back later into a homemade processor running on normal network programming, a slight frequency error could be detected in the restored audio. Also, when the station switched to local sync to run a local commercial, the frequency change could be heard. One of the major limitations of the Phonevision system was that due to the delay line being switched in and out, color could not be broadcast, as the 3.58 MHz phase lock necessary for NTSC color broadcasting could not be held. This limitation contributed to the demise of the system, along with the FCC authorization of subscription programming about 1969."

From:

http://en.wikipedia.org/wiki/Phonevision