GB1496132A - Facsimile system including apparatus for correcting the timescale of a signal derived from a dynamic magnetic recor - Google Patents

Abstract

1496132 Automatic control systems POST OFFICE 25 Feb 1975 [8 March 1974] 10412/74 Heading G3R In apparatus for facsimile transmission, a buffer store is filled with data signals read from a motor driven magnetic record, as sampled under control of clockpulses also derived from the record, and emptied by a master clock. The motor speed is controlled in response to the contents of the buffer. The input to the buffer from the sampler and the output from the buffer (which forms an analogue fascimile signal with corrected time scale) are respectively via a D-A converter and an A-D converter. In the embodiment, picture signals from a magnetic tape (or disc) are sampled at a rate determined by clock signals on line 7 also derived from the tape. These clock signals are used to enter the sampled signals into a buffer store 8 and to count up counter 16. The contents of buffer 8 are read out by pulses from master clock 9, which also reverses counter 16. The read-out of store 8 is used for facsimile transmission. Motor 3 driving the tape runs at a steady speed that is reduced in proportion to the contents of counter 16 i.e. the number of stored samples in buffer 8. The speed of response of the control may be modified by a direct frequency comparison between the clockpulses, derived from the tape, and pulses from the master clock 9. The buffer store 8 may include shift registers, logic elements and rotary or electronic switches, as Fig. 2 (not shown).