Patent GB-912607-A (GB)
Title: Improvements in frequency stabilised radio oscillation generators
IPC: H03L7/22
Filed: 1961-03-10
Abstract: 912,607. Frequency changing systems; combined radio receiving and transmitting circuits. COMPAGNIE INDUSTRIELLE DES TELEPHONES. March 10, 1961 [March 11, 1960], No. 8910/61. Classes 40 (5) and 40 (6). In an arrangement in which a continuously variable oscillator is synchronized at frequent and regular intervals over its tuning range with a set of frequencies derived from a crystal oscillator, the total frequency range is increased by transposing the oscillator frequency range to a higher frequency, by modulation with oscillations synchronized with the crystal oscillator, and beating the resultant with one or other of a number of crystal oscillators spaced regularly over a further frequency range. In an embodiment the frequency of oscillator 407, variable from 2 to 3 mc/s., is controlled at 10 kc/s. intervals from a fixed 1 mc. crystal oscillator 401, the latter frequency being reduced to 10 kc/s. in the divider chain 402, 403, 404, which is followed by harmonic generator 405. The latter includes output filters which pass 100 kc/s. wide bands covering 2160-3150 kc/s., a suitable band being mixed with the output from oscillator 407 in modulator 406 to give an output including a component between 151 and 160 kc/s. This is amplified by amplifier 408 which includes 1 kc wide filters with centres every kc. from 151 to 160 kc/s., by choice of a suitable one of which the desired output is selected from other modulation products and applied to a phase discriminator 410. The other input of the phase discriminator is derived from a crystal oscillator 409 comprising ten crystals spaced 1 kc. apart in the range 151-160 kc/s., from which a crystal is chosen which gives minimum beat frequency with the output from amplifier 408. The output from phase discriminator 410 is applied to thermionic reactance 411 which controls the frequency of oscillator 407 so as to reduce the difference frequency at the phase discriminator 410 to zero. To extend the frequency range of the system, a 28.5 mc/s. oscillator 412 is locked to crystal oscillator 401 by frequency comparison in a phase discriminator 413 of the output of oscillator 412 and 500 kc/s. derived from divider 402, the resultant controlling a thermionic reactance 414 so as to correct the frequency of the oscillator 412. The output of the oscillators 407, 412 is combined in a modulator 415 and passed to filter 416 passing the range 30.5-31.5 mc/s. The modulation product in this band is fed to a modulator 420 in which it is mixed with one of the frequencies from a crystal oscillator 417 comprising crystals covering the range 18-28 mc/s. in megacycle steps. Oscillator 417 is synchronized with oscillator 401 by means of phase discriminator 418 which controls thermionic reactance 419 by which the frequency of oscillator 417 is corrected. The difference frequency is taken from modulator 420 and passes to the output over band-pass filter 421 passing the range 1.25-13.5 mc/s. Mechanical control members 422, 423 comprising differential gears are coupled to a frequency indicating device 424 and control the variable capacity of oscillator 407, the choice of filter 408 and of the crystal in the oscillator 409 and also the choice of output filter in the harmonic generator 405; the megacycles are indicated directly by means of a coupling from the indicator 424 to the selecting device in oscillator 417. In a single sideband transmit/receive arrangement reversal of switches 425a-425e converts the arrangement from production of the transmitting frequency to generation of the correct local-oscillator frequency for superheterodyne reception on the frequency for which it is adjusted for transmission. For reception the output from oscillator 407 is combined in modulator 427 with 250 kc/s. from divider 426, the resultant beat frequency in the range 2.25- 3.25 mc/s. being separated out by filter 428. This is combined in modulator 415 with 27 mc/s. from oscillator 429 which is stabilized by means of phase discriminator 413 and thermionic reactance 414. The component in the output of modulator 415 in the range 29.25-30.25 mc/s. is filtered out by filter 430 and combined in modulator 420 with the output of the same crystal in oscillator 427 as is used for transmission, the difference frequency comprising the desired local oscillator frequency and being selected from the output by means of filter 421.