Patent GB-647643-A (GB)
Title: Improvements in frequency changing arrangements in radio transmitters and receivers
IPC: H03B21/04
Filed: 1946-08-16
Abstract: 647,643. Radio transmitting and receiving apparatus. SOC. FRANCAISE DES TELECOMMUNICATIONS. Aug. 16, 1946, No. 24484. Convention date, Nov. 23, 1942. [Classes 40 (v) and 40 (vi)] In apparatus for producing oscillations having a frequency variable over a continuous frequency band of the kind in which oscillations of stable high frequency are mixed with continuously variable low frequency oscillations, the stable high frequency oscillations are provided by a succession of harmonics of a piezoelectric crystal, the low frequency oscillator being variable to cover the interval between successive harmonics. Fig. 2 shows a transmitter which is continuously tunable over a range of 3,000 to 24,000 kc. and comprises an oscillator 1 continuously variable from 100 kc. to 200 kc. whose output is mixed at 3 with the output from a quartz oscillator 2 having a basic frequency of 100 kc. Harmonics having values 900 kc ... 1800 kc. are selected thus giving a sum frequency continuously variable over a range 1000 kc. to 2000 kc. which is selected by a tunable filter 4. A second series of stabilized frequencies, comprising harmonics having values 2000 kc....10,000 kc. of a quartz oscillator 5 of basic frequency 1000 kc., is mixed at 6 with the output from filter 4 to give a range of frequencies which are continuously variable over a range 3000 kc. to 12,000 kc. These frequencies are selected by a second tunable filter 7 and applied to a frequency doubler and selector 8, the output of which is continuously variable from 3000 to 24,000 kc. Tuning is effected by three knobs (not shown). The " thousands knob rotates in ten steps and selects harmonics from the oscillator 5, and effects the coarse tuning of filter 7 ; the " hundreds " knob similarly selects harmonics from the oscillator 2, and effects the coarse tuning of filter 4, and the fine tuning of filter 7 ; while the " units " knob tunes the continuously variable oscillator 1, and effects fine tuning of filter 4. Figs. 5 and 6 show a receiver for covering a continuous band of input frequencies from 0 to 24,000 kc. which are selected by a tunable filter 25 and applied to a mixer 26 fed by a quartz oscillator 27 of basic frequency 1000 kc., harmonics of which are selected so as to provide a first intermediate frequency which lies between 1000 and 2000 kc. This frequency is selected at 28 and applied to a mixer 29 together with a second local frequency which is continuously variable from 525 to 1525 kc., thus giving a fixed second intermediate frequency of 475 kc. The second local frequency is described by mixing at 33 the output from an oscillator 32, continuously variable from 125 to 225 kc., with the output from a quartz oscillator 31 of basic frequency 100 kc., harmonics of value 400 ... 1300 kc. being selected. The difference frequency is selected by a tuned filter 30. The second intermediate frequency is selected by filter 34, and may be further reduced by mixing with the output from a fixed oscillator 35 of frequency 474 kc. to give a tone output of 1 kc. Tuning is effected by knobs 39, 40, 41, Fig. 6. The " thousands " knob 39 moves in 24 steps to select harmonics of oscillator 27 and to effect coarse tuning of filter 25. The hundreds knob 40 moves in ten steps and selects harmonics of oscillator 31, effects coarse tuning of filters 28 and 30, and fine tuning of filter 25. The " units " knob 41 effects the continuous tuning of oscillator 32, and effects fine tuning of filters 28 and 30. Valve circuits corresponding to the above transmitter and receiver are described (Figs. 4 and 7, not shown).