GB850139A - Recirculating delay line - Google Patents

Abstract

850,139. Electric signal delaying systems. CANADA, MINISTER OF NATIONAL DEFENCE OF. Sept. 30, 1958 [Dot. 9, 1957], No. 31239/58. Class 40 (4). Signals are passed through a delay line or the like a plurality of times, being modulated on a different carrier for each passage. In one embodiment, Fig. 1 (not shown), the signal is modulated on a carrier of 25:5 mc/s, passed through the delay line from whose output it is selected by a suitable one of a plurality of filters and demodulated to produce an output, which is then modulated on a carrier of 26.5 mc/s. for a second passage through the delay line and so on until finally a tenth passage is made modulating a carrier of 34.5 mc/s. Outputs from the respective demodulators produce versions of the signal delayed by 1, 2 ... 10 times the delay of the delay line. In a modification, Fig. 3, the input signal is modulated on a 25 mc/s. carrier and after delay at 31 passes the lowpass filter 37 (cut-off 30 mc/s.) after which it is mixed with 60 mc/s. at 39 to produce a signal modulated on 35 mc/s. This signal after delay passes highpass filter (cut-off 30 mc/s.) 37 2 and is mixed with 61 mc/s. to produce a signal modulated on 26 mc/s. This process continues the signal alternately passing through filters 37 1 , 37 2 on different carrier frequencies. Suitable filters 35 1 ... 35 10 followed by demodulators (not shown) may be used to draw off the signal delayed by various multiples of the delay time of the delay line 31. A modification, Fig. 4 (not shown) uses lower frequencies for mixing at 36, 39, but requires filters 37 1 , 37 to be band-pass filters. In a further modification, Fig. 5, the recirculating path for the delay line comprises a frequency changer using a beat-frequency oscillator of 11 mc/s., the upper sideband being subjected to further frequency changing using a beat-frequency oscillator of 10 mc/s., the lower sideband being then selected, to produce overall a frequency shift of 1 mc/s. per passage around the loop. The delay line may be replaced by a magnetic tape if the signals are such as may be modulated on to audio-frequency carriers. Signals in some cases may be extracted from tappings on the delay line if convenient.