Patent GB-1160848-A (GB)
Title: Improvements relating to Frequency Synthesizers
IPC: H03L7/22
Filed: 1968-06-17
Abstract: 1,160,848. Frequency generators; automatic frequency control. C.I.T. -COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS. 17 June, 1968 [16 June, 1967], No. 28648/68. Headings H3A and H3F. A frequency synthesizer produces a plurality of different synchronized output frequencies from respective set frequency units 20-60 each of which is capable of being set by means of a general control unit 20 to a desired frequency set up in a frequency selector unit 10 which has controls 12 to select a desired frequency and switching devices 15 for choosing the unit whose output frequency is to be synchronized with the desired frequency. The general control unit 20 provides a spectrum of stabilized frequencies with any of which the chosen set frequency unit may be synchronized, a generator providing an exploratory control voltage to a variable oscillator in the chosen set frequency unit, and a modulating and filtering member connected to compare output frequency of the variable oscillator in the chosen set frequency unit with the frequency spectrum and providing output pulses for each frequency coincidence above a predetermined threshold frequency. The general control unit 20 also contains a pulse counter adapted to be preset to a number indicative of the desired frequency and to provide a switching signal changing the variable oscillator from exploratory control to a synchronized control when the number of coincidence pulses received corresponds to said preset number. Each of the set frequency units 30-60 contains, in addition to the variable frequency oscillator, a monitoring and filtering circuit in which the variable oscillator output frequency is modulated with the frequency spectrum received from the general control unit 20 to provide a first frequency, a phase discriminator comparing this frequency with a second stabilized frequency received from the general control unit 20 to provide a synchronizing control, and switching circuitry responsive to the switching signal from the counter in the general control unit 20 to change the variable oscillator from exploratory control to synchronized control when its output frequency coincides with the desired frequency set up in the frequency selector unit 10. The frequency selector unit may be remote from the other units and may comprise an automatic arrangement, the frequencies desired being set up in advance, e.g. on perforated tape. The manual control unit shown contains, in addition to the frequency selector knobs 12, associated visual indicators 13 indicating the frequency set up, and in addition to the switching devices 15 for choosing the unit to be controlled, visual indicators 14 which light up when the frequency indicated at 13 is obtained synchronized from the relevant set frequency unit. Subsidiary range knobs 16 each cover a section of the synthesized range of frequencies, switching into operation four corresponding oscillators in each of the set frequency units. The connection of the selected set frequency unit to the frequency selector unit is effected by an engagement control knob 11<SP>1</SP>, and a controller 17 enables resynchronization of one of the output frequencies to take place automatically if it has been lost accidentally; it consists of a memory in which is stored each of the desired frequencies, coupled to a logic circuit which automatically operates the controls of the frequency selector unit to repeat the exploratory and synchronizing processes. In another embodiment (Fig. 4, not shown) the frequency selector unit includes monostable multivibrators individually selectable to synchronize respective set frequency units with desired frequencies set up in succession in the frequency selector unit, the general control unit having groups of AND gates equal in number to the number of set frequency units associated with the synthesizer, the variable oscillators of these set frequency units being selectively connectable through one of the groups of AND gates to the exploratory control voltage generator by the monostable multivibrators.