Patent GB-1357860-A (GB)
Title: Tuning indicator
IPC: H03J3/14
Filed: 1972-09-20
Abstract: 1357860 Tuning indicators; stereophonic radio receivers SONY CORP 20 Sept 1972 [20 Sept 1971] 43652/72 Headings H3Q and H4L In a frequency-modulation receiver a tuning indicator of visual type operates in dependence upon a noise signal derived from the F.M. detector. The noise output in the audio output from a frequency-discriminator, obtained, e.g. by means of a filter comprising a circuit tuned to 80 Kcs., has the amplitude characteristic shown in Fig. 1c, in which f o  is the correct tuning frequency. Such a filter 22, Fig. 3, connects the discriminator output to three voltagedoubling rectifiers comprising diodes 36, 37; 36A, 37A; and 36B, 37B respectively, the outputs from which form the base biases for transistors 41, 41A, and 41B respectively, in whose collector circuits are lamps 42, 42A and 42B respectively. In addition, standing biases are applied via resistors 40, 40A and diodes 39, 39A so that the transistors 41, 41A, 41B beome conductive in turn, at the levels a, c, b (Fig. 1c) respectively, so that the corresponding lamps 42, 42A, 42B are illuminated. A simplified embodiment is also described on the Specification, in which only one lamp is provided (Fig. 2, not shown). In a modification, each of the transistors 41, 41A, 41B, Fig. 4, has its collector coupled to the base of a corresponding transistor 43, 43A, 43B, the emitters of which are connected together and to the emitter of a further transistor 47, there being a common emitter circuit resistor 46. The base of the transistor 47 is biased by means of resistors 49, 50, while its collector circuit provides base bias for a transistor 56, by means of resistors 48, 53, 54 and Zener diode 52. The collector circuit of transistor 56 controls a further transistor 58, the collector to emitter path of which forms a shunt on the input circuit of transistor 60 which has lamp 62 in its collector circuit and is driven from a voltage derived from the I.F. circuits of the receiver and applied to terminal 61. If one or more of the transistors 43-43B is conductive, corresponding to one or more of the lamps 42-42B being illuminated, transistor 47 is biased conductive, whereby transistor 56 is non-conductive and transistor 58 conductive to prevent lamp 62 being illuminated: when all the lamps 42-42B have been turned off all transistors 43-43B are conductive whereby transistor 47 is biased non-conductive, rendering transistor 58 non-conductive also. The input at terminal 62 can then render lamp 62 illumiuated. The lamps 42-42B and 62 may be arranged side by side with intervening partitions and behind differently coloured transparent windows (Fig. 5, not shown). In a further embodiment, only one lamp is on at a time; in this, the bias on diode 39, Fig. 8, is derived from the collector circuit of the transistor 41A, so that when this transistor becomes conductive and lamp 42A illuminated, the standing base bias on transistor 41 falls, so that it becomes non-conductive. The bias on diode 39A is similarly derived from the collector circuit of transistor 42B, while a clamping diode 78 prevents the bias on transistor 42 rising when transistor 41A is cut off on transistor 42B becoming conductive. Each of the lamps 42- 42B may be replaced by a series-connected pair 42<SP>1</SP>, 42 &c. arranged around the lamp 62, Fig. 7. Stereo/mono indicator.-In a stereophonic receiver transistors 82, 85, Fig. 8, having lamps 83, 86 respectively in their collector circuits are arranged in series with the lamp 62, so that when it is illuminated one of the lamps 83, 86 is also illuminated. A control signal from the stereo decoder is applied to terminal 81, and when present renders transistor 82 whereby lamp 83 is illuminated and transistor 85 cut off, rendering lamp 86 unilluminated: in the abscence of a control signal, transistor 82 is cut off and biases transistor 85 conductive.