GB1339173A - Data handling systems - Google Patents

Abstract

1339173 Selective signalling ELLIOTT BROS (LONDON) Ltd 15 Jan 1971 2011/71 Heading G4H A data handling system responsive to the frequency spectrum of an input, converts the input into a rectangular waveform having two amplitudes, one of which operates a counter, a less significant part only of the count being sampled periodically and transmitted (or only a single less significant digit of a count may be actually accumulated in the counter). In a system disclosed, an electrical waveform from a sound transducer is amplified, band-pass filtered and then clipped to a rectangular waveform which switches amplitudes at the zerocrossings, to gate clock pulses from a pulse generator to a counter. The count is periodically sampled by the pulse generator acting through a frequency divider, with or without subsequent resetting of the counter, and the counts are transmitted to a receiver at which each is converted to an analogue pulse amplitude. These pulses are lengthened to give a stepped analogue waveform which is fed to a bank of filters. As a modification forming an embodiment of the invention, only one stage of the counter has its state sampled and transmitted (the counter not being reset after each sampling). Alternatively, the rectangular waveform may simply switch a flip-flop, the state of which is sampled and transmitted. The frequency may be increased by a frequency changer before the band-pass filter. The total amplitude of the energy received by the transducer could be signalled by inserting a frequency modulator before the bandpass filter to give an amplitude to frequency conversion, or a reference signal could be added at this point so that the transmitted information represents not only the relative amplitudes of the various frequency components received but also their amplitudes relative to the reference signal, from which the overall (total energy) amplitude may be derived at the receiver. The receiver may alternatively be a digital computer with a Fast Fourier Transform programme. Another embodiment has a ring of 8 sound transducers feeding respective channels, the count signals in the different channels being sampled in turn, transmitted, and distributed at the receiver to 8 output channels each of which delays the signals received and feeds weighting and summing units in all the output channels from the delay, the delaying, weighting and summing being such that the output in each channel, obtained via a band-pass filter, represents the total sound energy received by the ring of transducers from a respective direction, and contains frequency spectrum information for that direction. Application to radio (instead of sound) is mentioned.