Patent GB-715190-A (GB)
Title: Improvements in or relating to remotely controllable variable frequency oscillators
Inventor: BROWN THOMAS THEODORE
IPC: H03L7/183
Filed: 1952-12-23
Abstract: 715,190. Electronic counting apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Aug. 26, 1953 (Dec. 23, 1952], No. 32652/52. Class 106 (1). [Also in Group XXXV] An automatic control system for tuning an oscillator to any one of a plurality of spaced selectable frequencies by means of a motor, and for maintaining the frequency at its selected value, comprises means for deriving from the oscillator a frequency in predetermined arithmetical relation to the oscillator frequency, and a stable reference oscillator repeatedly allowing passage of the derived frequency to an electronic counter for predetermined time intervals. The desired frequency is set up by selectable switch means (preferably in decade fashion as hundreds, tens and units of kilocycles, and remotely controlled), and error-detecting means actuated in dependence on any difference between the counter reading and the switch setting, are used to control a reversible motor which adjusts the tuning of the oscillator to remove this difference by varying the counter reading. In the Fig. 1 embodiment, the oscillator is a back-coupled valve V1 tunable over e.g. a range of 1-2 mc/s by a variable condenser C driven through a mechanical link CD by a motor M. A frequency-divider FD converts the output to a lower range (e.g. 10-20 kc/s) and this derived frequency is fed intermittently through a switch SWC to a cascade of dekatron counters DA, DB, DC arranged respectively to register units, tens and hundreds of cycles of the derived wave. The shaft S of the switch SWC is rotated, e.g. at one revolution per second, by a synchronous motor which may comprise a phonic wheel PM driven by a coil in the anode circuit of a crystal-controlled oscillator V3 operating at 1 kc/s. The contact of the switch SWC may occupy one tenth of the rim so that the derived wave is fed to the counter for one-tenth of a second and is cut off for nine-tenths. Thus during each closure of the switch SWC the counter registers a count equal to the frequency in kc/s of the oscillator VI. The positive supply for the anodes of the dekatrons is interrupted for a short period and is reconnected by a switch 2 SWC just before closure of the switch SWC, thus restoring all the counters to zero position, ready for the next count. The desired frequency is set up in decade fashion by rotating switch members SSA, SSB, SSC to such positions that terminals Y are connected to the desired digits of the dekatrons and terminals X and Z are connected to all the undesired digits above and below those desired. As shown in Fig. 1, the switches are set for 735 kc/s, and if during each closure of the switch SWC the counter DA registers less than 7 or over 7, one or other of the relays RWR, RWF is operated to start the motor M in the direction required to increase or decrease the oscillator frequency. When the frequency reaches the range 700-799, the motor is cut out and a relay RWS connected to terminal Y is energized and switches the relays RWR, RWS, RWF, to the terminals X, Y, Z, of the counter DB. A similar action takes place at this counter, and finally at the counter DC, the motor being finally arrested with the oscillatory frequency at 1735 kc/s. The initial numeral 1, being the same for all frequencies within the operative range, can be ignored. Phase locking of the oscillator is effected by connecting its grid circuit to the output of a double valve V4 which produces short pulses at a repetition frequency 1 kc/s, being fed from the crystal-controlled oscillator V3. Harmonic frequencies at 1 kc/s spacing are thus supplied, and the oscillator V1 is locked to the harmonic corresponding to the oscillator tuning. The rotary switches SWC, 2 SWC may be replaced by electronic switches In a second embodiment (Fig. 2, not shown), the hundreds dekatron DA and the frequency divider FD are omitted. The motor M drives not only the tuner C but also a device arranged to supply any one of ten frequencies spaced at 100 kc/s in the range 1-2 mc/s. That one of the ten which is nearest to the frequency set by the tuner C is supplied to a heterodyne mixer, and the beat frequency is fed through a low-pass filter, with a cut-off at 50 kc/s, to the switch SWC and to the two dekatrons DB, DC. The ten frequencies may be derived from ten crystals, or they may be selected from harmonics generated by a pulse producer fed with 100 kc/s input derived from the 1 kc/s source V3.