Patent GB-996311-A (GB)
Title: Improvements in or relating to systems for measuring distance by electromagnetic waves
IPC: H03B5/36
Filed: 1963-07-26
Abstract: 996,311. Measuring distances electronically. ALBISWERK ZURICH A.G. July 26, 1963 [July 27, 1962], No. 29723/63. Heading H4D. In a system for measuring distances between stations by means of electromagnetic waves, in which a first station at one end of a distance to be measured emits electromagnetic waves of a first frequency and a second station at the other end of the distance emits electromagnetic waves of a second frequency differing from the first frequency by an audio frequency, at least one of the stations is capable of emitting either said first frequency or said second frequency as desired, by means of a crystal oscillator having a reactive element circuit which is switchable into the oscillator to alter the frequency of the oscillator by the audio frequency difference. The invention is described as applied to systems of the type wherein, at say the second station, the received waves of the first frequency are mixed with the locally generated waves of the second frequency to produce a beat signal at the audio frequency, the beat signal is divided down by a whole number greater than one, and the resultant is modulated on the wave of the second frequency which is then transmitted to the first station. The wave is then received at the first station and the beat signal extracted therefrom by detection and multiplication by said whole number, and compared in phase with a beat signal of like frequency obtained by mixing the received carrier of the second frequency with the locally generated signal of the first frequency. In cases of triangulation, at least one of the three stations involved must be capable of operating at the first frequency or at the second frequency so as to be capable of co-operating separately with the other two stations. In addition each of said first or second frequency must be variable so as to provide a fine but ambiguous measuring system and a coarse but unambiguous measuring system. The Figure shows part of a station wherein switch S2 changes the station from a first frequency station to a second frequency station, whilst switch S1 changes said first or second frequency from a coarse to a fine frequency. The station generally comprises an oscillatory circuit including transistor H1, limiting diodes D1 and D2, transformer T and a tuned crystal circuit formed of either crystal Q1 and its tuning capacitors C1 and C3 or crystal Q2 and its tuning capacitors C2 and C4. The particular crystal circuit is chosen by means of biases on diode D6 or D7 produced by means of switch S1. The change in the frequencies of the crystal circuits by the audio frequency difference is produced by semiconductor diodes D3, D4 and D5, which, in the position of 52 shown act as resistances, but in the second position act as variable capacitors under the control of a negative potential at terminal R. The output of the oscillator circuit is taken from terminal A, via buffer transistor H2. One of the diodes D3, D4 and D5 may be replaced with a fixed capacitor, or they may be replaced by a capacitor in parallel with a switching diode. The first and second frequencies may be modulated on to carrier waves, either as amplitude modulation or as frequency modulation. The invention may be applied to a system as described in Specification 811,762. Specification 671,661 also is referred to.