GB521330A - Improvements in or relating to superheterodyne wireless receiving sets - Google Patents

Abstract

521,330. Radio receiving sets. PHILIPS LAMPS, Ltd. May 8, 1939, No. 13766. Convention date, May 11, 1938. [Class 37] [Also in Group XL] In a superheterodyne wireless receiver adapted to cover several waveranges band-spreading is provided for certain very narrow bands within the waveranges. For these bands the tuning circuits are fixed at the centre of the band, and tuning is effected by means of a subsidiary tuning condenser which alters the oscillator circuit only. As shewn six waveranges cover the bands 11m. to 19m., 18m. to 30m., 29m. to 54m., 52m. to 177m., 172m. to 570m., and 740m. to 2100m., and band-spreading is provided for the narrow bands at 14m., 17m., 19m.. 25m., 31m., and 49m. Wavechange switches 10, 20 and 40 are moved so that members 48, 18, 28 and 38 make their respective contacts in the usual way. Condenser 34 is the normal oscillator tuning condenser. When the circuits are set to one of the bandspreading positions, contact 33 changes over, as in the manner described below, so that the circuit of the oscillator valve includes condensers 35 and 36 and the circuits controlled by switches 20 and 50. Switch 50 makes its lower contacts for three of the band-spreading positions and its upper contacts for the other three. For the 14 meter band, therefore, the oscillator frequency-determining circuit comprises the parallel combination of coils 1 and 9 and condensers 35, 36 and 54 ; for the 17 meter band, the combination is coils 1 and 9 and condensers 35, 36 and 55 ; for the 19 meter band coils 1 and 2 and condensers 35, 36 and 56 ; for the 25 meter band coils 1 and 2 and condensers 35, 36 and 57 ; for the 31 meter band coils 2 and 3 and condensers 35, 36 and 58 ; for the 49 meter band coil 3 and condensers 35, 36 and 59. The member 30 operated by control 20 enables coil 2 to be used on one only of the bands in the third waverange. A suitable mechanism for changing the connections is indicated in Fig. 2. Springs 110 rest on the surface of cams such as 101 which are driven by the main tuning shaft 100 of the receiver, the individual springs being tensioned as required by members 118, 119, 120 driven by the wave-change switch. When a wavespreading position is reached, the tensioned spring drops into a notch such as 104, and a switch such as 132 is changed over. The circuits are restored to normal by continued movement of the main tuning shaft 100.