NAEB Engineering Newsletter (Aug 1955)

scope. We wish it were possible for every engineer in educational broadcasting to attend this exhibit of broadcasting equipment. We would also wish that they might hear the papers presented at the Broadcast Engineering Conference held in connection with this convention. Perhaps in the next year some arrangement can be made so that those who have the time, the desire, and the means can attend. a#*#-###*### Also of interest in educational circles were two demonstrations being held contin¬ uously last week in Washington: FM Multiplexing and Phonevision. The Multiplex Services Corporation, in cooperation with WGMS (FM) of Washington were demonstrating their FM Multiplex equipment manufactured by Gates Radio Company. By "multiplexing” we mean the transmission simultaneously without interference of more than one program on a single FM channel. One program is transmitted on the regu lar FM channel which may be picked up on the ordinary FM receiver. One or more pro¬ grams may be "multiplexed” over this regular program by the use of special equipment. These multiplexed programs are sent out on a super audible subcarrier in addition to the public broadcasts. If only one program is multiplexed, ihe full 50-15,000 cycle FM frequency range may be transmitted; however if more than one program is multi¬ plexed, the audio frequency range of each multiplex channel is limited to 50 to 85000 cycles. Obviously special receiving equipment must be employed to receive programs transmit¬ ted on the subcarrier (s). ‘The FCC has recently amended its rules to permit FM broad¬ cast stations to use multiplex methods for the transmission of income-producing subsidiary services such as storecasting, transitcasting, and functional music. It would be possible for educational stations to employ multiplexing in an FM network operation. The network program could either be transmitted to the next relay station on the main channel if it were to be carried locally or if a local program were scheduled at this time the net program could be transmitted on the multiplex channel. Schaefer Custom Engineering also had FM equipment on display; however tine did not permit us to see their equipment* The Zenith demonstration of Phonevision also was of considerable interest. Some ed¬ ucators feel that some such system of scrambled television pictures may be an an¬ swer to the problem of securing tuition for college or other courses televised for credit. In Phonevision, both audio and video are scrambled. The audio portion unscrambled, sounds a bit like inverted speech; the picture version is scrambled by changing picture polarity (i.e. blacks are white and vice versa) as well as horizontal dis¬ placement of groups of lines. Each subscriber’s TV set is equipped with a decoder which must be set properly for each program it is wished to receive. In the dem¬ onstration system used, programs were numbered end on a punch board. By punching the proper program number on the board, the code number (five digits) is uncoverd to which the receiver decoder must be set to receive the program. Each set must have an individual combination set up, otherwise the code number for a particular program coulc be passed around.for friends and neighbors to use. The system might also be set up so that the subscriber could purchase decoding information at coin machines, utilize a coin box mechanism on the set or call a Phonevision operator for decoding information.