Patent GB-580528-A (GB)
Title: Improvements relating to systems for the transmission and reception of radio-electric waves with great precision of standardisation
IPC: H04B1/034
Filed: 1942-08-26
Abstract: 580,528. Wireless apparatus. SOC. FRANCAISE RADIO-ELECTRIQUE. Aug. 26, 1942, Nos. 12047 and 12048. Convention dates, Jan. 26, 1940, and Aug. 3, 1940. [Class 40 (v)] [Also in Group XXXVI] A receiver or transmitter is tuned over a very wide frequency band by heterodyning with a number of fixed frequencies to produce a series of spaced frequencies, the spaces being covered by heterodyning the spaced frequencies with a variable oscillator having a range equal to the differences between the spaced frequencies. Fig. 1 is a schematic circuit diagram showing the invention applied to a receiver which can be continuously tuned to receive frequencies from 250 kc. to 2500 kc. For the lower part (250 kc. to 750 kc.) of the frequency range the aerial 14 is connected by the left-hand side of switch 15 to the input of a preselector block 1 tunable from 250 kc. to 750 kc. comprising tunable circuits 2, 3, 5, amplifier 4 and a mixer 6 fed from an oscillator 7 accurately tunable over a range 375-625 kc. This produces an output at 125 kc. which is fed to a band-pass filter 9 and a second mixer 11 fed from a fixed oscillator 12 to give an output which passes to block 13 comprising an A.V.C. detector and L.F. amplifier. For the remainder of the range (the upper part 750-2500 kc.), the aerial 14 is connected at 15 to a preselector block 16 comprising circuits 17, 18, 20 tunable over the range 750-2500 kc. and a mixer 21 fed by a stable quartz oscillator 22 which can be set to give either 1250 kc. or 1750 kc. The output from mixer 21 is fed to the input of block 1 and is dealt with as described for a signal in the 250-750 kc. range. By tuning block 16 and using both the sum and difference frequencies resulting from the two frequencies of oscillator 22, a received signal anywhere in rhe range 750-2500 kc. is made to produce an output at 21 which lies in the frequency range 250- 750 kc. and which can be handled by block 1 and the remaining stages. Fig. 5 shows apparatus for effecting the continuous tuning of the circuits of Fig. 1 from 250-2500 kc. by the rotation in one direction of two control handles. The frequency range is divided into nine sub-ranges of 250 kc. extent and one control handle, the wave range handle has discontinuous movement into nine positions for setting the apparatus ready for continuous tuning in the selected range by means of the second control handle. The wave range handle, not shown, drives a spindle 39 through one revolution for each wave range and this, by means of Maltese Cross gear 40 advances a selector drum 30 through one-ninth of a revolution. During the first part of the revolution of spindle 39, a cam 42 rotates a lever 43, 44 which through parts 45, 48, 49 unlocks the differentials 25, 26 operating condensers 58, 59 of the preselector blocks 1 and 16. At the same time a set of levers 31 are rotated in a clockwise direction to remove their noses from engagement with apertures in the selector drum 30. The drum 30 can then be rotated into the position corresponding to the desired wave range, and levers 31 are released on the delayed return of lever 43. According to whether or not there is an aperture in drum 30 opposite to the nose of a lever, the lever will return to the position shown or will remain displaced, and thus the positions of setting rods 35 ... 38 and 67 coupled to the levers 31 are determined in accordance with the requirements of each range. Rods 35, 36 act through sectors 60, 62 on the differentials 25, 26 to effect the initial settings of condensers 58, 59 of preselector blocks 1 and 16. Rod 37 controls change over switches 64, 65 to switch in or out one or other of symmetrical stators of the condensers in block 16 to reverse the sense of the change in capacity for the same sense of rotation of the condensers in block 1 and oscillator 7 according as sum or difference frequencies are being used in the particular sub-range selected. Rod 38 controls switch 23 for selecting the appropriate frequency of quartz oscillator 22 and rod 67 operates aerial switch 15. When the appropriate range has been set by these means a continuous tuning hand wheel 69 selects the particular frequency within the range. Hand wheel 69 drives spindle 68 and through gear 70, spindle 71, and worm 72 drives spindle 73 of condenser 74 in heterodyne oscillator 7. Also spindle 68 through gears 75, 76, 77 drive the differentials 25, 26 controlling condensers 58, 59 in blocks 1 and 16. The gearing is such that when condenser 74 passes through its full range, the condensers in block 1 pass through half the range, and in block 16 through one-fourteenth of the range. This corresponds to a range of 250 kc. and thus the unit drum 79 of an indicator 80 is driven from spindle 71 through 25 revolutions. Also since rotation of the wave range spindle 39 through one revolution corresponds to 250 kc., gearing 83 ... 87 acts through differential gear 82 to advance the tens drum 81 through two and a half revolutions. All the variable condensers have a linear frequency variation, and oscillator 7 is temperature compensated. The invention may also be applied to a transmitter having a continuously variable frequency.