GB570636A - Improvements in tuning arrangements for radio-receivers - Google Patents

Abstract

570,636. Testing radio apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and BEANLAND, C. P. Oct. 22, 1943, No. 17441. [Class 40 (v)] [Also in Group XXXVI] - A radio receiver includes a stabilized oscillation generator, means for feeding harmonics of the fundamental frequency of said oscillation generator into the aerial circuit of said receiver, and means for producing signals in the output of the receiver when the receiver is tuned to respond to frequencies corresponding to said harmonic frequencies said signals serving, in co-operating with a tuning control device, as calibration checks for said receiver. The invention is described for a receiver covering four ranges, viz. 2-4 m.c. ; 4-8 m.c. ; 8-16 m.c. ; and 16-32 m.c. The receiver is provided with a crystal-controlled calibration oscillator having a fundamental frequency of 500 kc., and thus the limits of the four frequency ranges coincide with harmonics of the calibration oscillator. The output of the oscillator can be fed to the input of the receiver and the final I.F. is mixed with the output of an auxiliary beat oscillator to produce an audible signal whenever the receiver is tuned to a frequency corresponding to one of the harmonics of the calibration oscillator. The main tuning control of the receiver, Fig. 1, is under the control of a knob driving a vernier disc rdv and main disc rod coupled by a cord co to an index rp moving over a scale CS. The scale CS is in the form of a cylinder bearing scales corresponding to the four wave ranges and is rotated on operation of the wave range switch to bring the appropriate scale under the index rp. One complete traverse of the main disc rdm moves index rp and the tuning condensers through one wave range. The scale CS has an upper scale (2-4 m.c. as shown) which is non-linear and is subdivided at the factory by the use of test oscillators to include check points corresponding to the harmonics of the calibration oscillator. Beneath this scale are markings showing for each subdivision the number of kilocycles through which the receiver is assumed to be tuned for one division of the main disc rdm. To tune accurately to a short wave station of known frequency, the calibration oscillator and auxiliary beat oscillator are switched on and the receiver is set to the nearest check point on the scale CS below the desired frequency and then tuned to obtain an audible signal from the corresponding harmonic of the calibration oscillator. The readings of the main and vernier discs are taken and then, from the lower scale of CS giving the number of kcs. per division at that part of the scale, the true reading of the main and vernier discs for the desired frequency is calculated. This reading is slightly too high as the scale is non-linear. The process is repeated, but this time working downwards from the next check point above the desired frequency. This reading is slightly too low for the same reason, and the mean of the two readings is accurate to about one part in four hundred. The calibration oscillator is then switched off, and the auxiliary beat oscillator is left on only if it is required for the reception of continuous wave signals. Specification 569,567 is referred to.