GB472502A - Improvements in multi-band radio receivers - Google Patents

Abstract

472,502. Wireless receiving circuits. HAZELTINE CORPORATION. April 20, 1936, No. 11254. Convention date, May 25, 1935. [Class 40 (v)] In a radio receiver adapted for operation over a plurality of wavebands, the L.C. ratios for the several bands are of the same order of magnitude, the effectiveness of the tuning element being so varied with the band selected that the full range of each band is substantially covered by the full movement of the tuning element. Fig. 3 shows a superheterodyne receiver suitable for operation over six wavebands, the lowest of which covers the general broadcast band. The radio-frequency inductances 14a ... 14f are coupled to the aerial by the three coupling coils 111, 112, 113 and are each tuned by the variable condenser 20 when switched into circuit by the selector switches 70, 74. These switches are associated with banks of semi-fixed condensers 73b ... 73f and fixed condensers 77b ... 77f, the latter being selectively connected in parallel with condenser 20 and the former in series with this parallel combination across the corresponding inductance 4. The values of the condensers 73, 77 are so chosen that for each waveband the effective value of condenser 20 is reduced to that which gives full scale tuning on each waveband. The intervalve coupling between the high - frequency amplifier 17 and the oscillator-modulator 24 is exactly similar, inductances 26a ... 26f being tuned by condenser 30 and condenser banks 83 ... 87 selected by switches 80, 84. The switches 74, 84 and the condensers 77, 87 may be dispensed with by connecting the condensers 73, 83 across their appropriate inductances and tuning to the mid-frequency of the respective bands ; the general broadcast band circuits 14, 26 are tuned by condensers 20, 30, Fig. 2 (not shown). In another modification, one inductance 14a and condenser 20 are employed for the broadcast band and one inductance only for all the remaining high-frequency bands, tuned by condenser 20, condensers such as 73, 77 and switches 70, 74 of Fig. 3 being employed to effect the necessary variation in effective capacity of 20 for the several wavebands, Fig. 4 (not shown). A further modification is shown in Fig. 6, in which the relatively large condenser 20 is used for the general broadcast band, with inductance 14a, the small condenser 107 being used for the higher frequency bands with the bank of compensating condensers 108. The condensers 107, 20 may be combined in one assembly and unicontrolled. The condenser 107 may be dispensed with and the condenser 20 used also for the higher frequency bands by connecting a small condenser in series therewith by the switch controlling the high-frequency inductances, Fig. 7 (not shown).