GB1330970A - Distance measurement systems - Google Patents

Abstract

1330970 Radar SIEMENS-ALBIS AG 23 Dec 1971 [22 Jan 1971] 60030/71 Heading H4D A distance measuring system includes stations mounted at each end of a distance, each transmitting a different measuring signal modulated on to different carrier waves and each station mixes transmitted and received signals to provide a difference signal which is reported back from one (subsidiary) station to the other (main) station by means of an in phase pulse train modulated on to the local carrier signal wherein the pulse train comprises pulses each of which is bipolar and the frequency spectrum of which contains substantially no component at the pulse repetition rate (i.e. the difference signal frequency). In the subsidiary station the difference signal is first squared up (Fig. 2a) and then added to an inverted delayed version of itself (Fig. 2b) to produce pulses indicating the zero crossings (Fig. 2c). These pulses generate a single cycle bipolar pulse (Fig. 2d) by means of a R.C. tuned circuit whose time constant equals the pulse width #. These bipolar pulses are used to frequency modulate the carrier signal which on reception by the main station undergoes filtering to derive the reference difference signal and frequency discrimination to detect the reported back difference signal. The phases of the two difference signals are compared to determine the distance between the two stations. Since the bipolar pulse train contains virtually no component at the difference frequency (Fig. 2h), cross-talk is greatly reduced.