Patent GB-447396-A (GB)
Title: Improvements in or relating to radio receivers
IPC: H03J3/10
Filed: 1934-08-15
Abstract: 447,396. Valve circuits for wireless reception. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of Carlson, W. La V.; 726, Clinton Avenue, Chittick, K. A.; 120, Wayne Avenue, both in Haddonfield, and Conron, W. H.; 301, Bank Avenue, Riverton, both in New Jersey, U.S.A.) Aug. 15, 1934, Nos. 23593 and 23594. Void [Abridged as open to inspection under Sect. 91 of the Acts, Feb. 16, 1935]. [Class 40 (v)] In a superheterodyne receiver a predetermined intermediate frequency is produced on one waveband by heterodyning with the fundamental frequency of the local oscillator and on another waveband by using a harmonic of said oscillator. In one embodiment, Fig. 1, a radio frequency amplifying pentode 1 is followed by a detector oscillator pentagrid 31 and intermediate frequency amplifier and second detector 119. The tuned circuits 13, 29 associated with the valve 1 and the signal portion of valve 31 respectively comprise coils 19, 45 respectively, tuned over the lower frequency range by ganged condensers 23, 47 respectively, the signals in this range beating with the fundamental frequency of the oscillator portion of valve 31, which is determined by circuit 100, to produce the fixed intermediate frequency. The coils 19, 45 with their inherent capacities are broadly tuned to a narrow highfrequency band which is brought into use by a switching arrangement 53 adapted to open switches 27, 51 and thereby introduce small trimming condensers 25, 49 in series with the condensers 23, 47 respectively. Thereafter, the variation of the latter has but little effect on the tuning of the circuits 13, 29 and the oscillator condenser 103 may be adjusted until the incoming signal produces the fixed intermediate frequency by beating with a predetermined harmonic present in the oscillator output. In a modification, Fig. 2 (not shown), switches may be arranged to disconnect the main tuning condensers and connect small trimming condensers in parallel with the tuning coils, for the high-frequency range. In a second embodiment, Fig. 3, the wave-band switching is arranged to allow the reception of two wide bands, the ganged condensers 23, 47 being operative on both bands, the higher band being introduced by the short-circuiting of a portion of the inductances 19, 45 by switches 141, 179 respectively, the simultaneous introduction of condensers 147, 185 coupling the coils 19, 45 to their primary windings and trimming condensers 145, 183 by switches 143, 181, and the introduction of a trimmer 219 across the oscillator condenser 103 by switch 217. The signals in the higher wave band beat, as in the first embodiment, with a predetermined harmonic of the locally generated oscillations, to produce the intermediate frequency. The construction of the coils and wave-range switch is described, Fig. 4 (not shown), the latter embodying some of the trimming condensers. In a modification, a further switch may, for the higher band, introduce a condenser of about double the capacity of and in series with the main tuning condenser of the tuned circuits. Alternatively, each highfrequency transformer may comprise two independent secondary windings alternatively switched into circuit for the two bands. The tuned circuits may be isolated from earth as regards direct current in known manner for the introduction of A.V.C. potentials to the grids of their associated valves. The locally generated oscillations are preferably of a fundamental frequency higher than that of the received lower frequency wave-band, and the selected harmonic thereof preferably lower than that of the received higher wave-band.