Multitrack Recording of Reduced Bandwidth TV Signals

The system described here was developed in order to record the pseudorandom scan television signal developed by Deutsch. The objective was to investigate the possibility of recording a 200 kHz video signal on a 1/4 in tape running at 15 in/s. The difficulties which arise in such a task are two-fold: 1) bandwidth limitations of the recorder; and 2) flutter and skew of the recorder. Since a tape recorder at this speed has a bandwidth of about 45 kHz, time-division multiplexing was used to reduce the signal into low-frequency signals. The problem is to reassemble the signals at playback. This is a difficult task since these signals are shifted in time randomly by flutter and skew. Experiments disclose that the skew is linearly distributed across the tape; therefore, by knowing this time shift between two tracks at any instant, the position of the appropriate sample at any other track can be predicted. For skew and flutter compensation purposes two reference signals are recorded on the two outer tracks of the tape. The phaseshift of the reference signals at playback is used as a measure for the skew prediction system for each track. Thus the video signals are sampled at the correct value. In order to reassemble the samples in the correct time sequence, they are stored in analog memory cells. The memory cells are read out with the aid of an oscillator which is in turn synchronized with flutter. The deflection waveforms are also generated synchronous with this oscillator.