GB1281061A - Channel selector and tuner combination - Google Patents

Abstract

1281061 Tuning circuits; gating circuits; colour television MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 25 Aug 1969 [30 Aug 1968 1 Oct 1968 (2) 3 Oct 1968 4 Dec 1968 21 Feb 1969] 42298/69 Headings H3Q H3T and H4F [Also in Division G4] A channel selector controls a tuner having variable capacitance diodes as tuning elements by means of n signals of binary "1" or "0" to select one of 2<SP>n</SP> channels. As shown in Fig. 12 the binary code required is set up in bi-stable circuits 95-98 so that one column of diodes of the diode matrix 151 are biased off, such as column 1, whereas at least one diode in each of thr other column is biased on. This biases the diode 108 connected to column 1 on so that the voltage set by potentiometer 88 is applied to tune the capacitance diodes 84-87 of a colour television to channel 1. The diodes 109-114 connected to the other columns of the diode matrix 151 are biased off. The channel selected is indicated by a lamp, neon or number indicating tube controlled by a transistor 52 associated with the selected channel. A pulse generator or astable multivibrator 137 is started by closing switch 139 and the bi-stable circuits 95-98 then count the output pulses from generator 137 so as to alter the code stored in the bi-stable circuits and sequentially change the channels until the required channel is obtained. The channels may be sequentially tuned in either direction by means of change-over switch 147- 150 or by a change-over switch (153-155, Fig. 15, not shown), interchanging the input-output connections between the bi-stable circuits 95- 98. Channel selection can be obtained by pressing a push button and remote control may be achieved by applying a coded pulse train to the bi-stable circuit 95. In a modification (Fig. 10, not shown), where the television has a monitor Braun tube (135, Fig. 9, not shown) and a colour telecast indicator (136) if when the channels are being sequentially selected by the operation of the pulse generator 137 a selected channel is telecasting in colour a signal is picked up from the mixer 82 and is detected by a diode 145. This detected signal in the form of the colour carrier signal is passed via a video amplifier 144 to operate a transistor 142 which turns on an indicator lamp 141 during telecast reception and turns this lamp off when the telecast is interrupted. The television signals broadcasting on the different channels are monitored on the monitor picture tube (135). The number of channels to be selected may be varied by varying the number of stages of the counter 95-98 or by applying negative feedback. In an alternative embodiment (Fig. 16) the channel selector is formed as an integrated circuit 160 having an integrated circuit 169 for applying output 168 to the channel indicators and having a frequency discriminator circuit 158 for effecting AFC. To match the integrated circuit to the receiver a trimmer capacitor may be provided. Motor driven tuning (Fig. 5).-The channel selected corresponds to a frequency f 1 -f 4 selected from an oscillator 51 which is received at 52 and tuned by circuits 53. On rotation of a motor 59, each time a different number is indicated on a dial 58 the contacts 63 open and close to produce a pulse input for bi-stable circuits 66-69. When the outputs from the bi-stable circuits 66-69 and from the tuning circuits 53 produce a zero output from the comparator C1-C4 transistor 61 cuts off to stop the motor 59. The selected tuning voltage is applied to the variable capacitance diodes of the tuner via 72 and 77. Waveband switching between high and low VHF bands may be obtained by a switching diode by means of a waveband switch 79. In a prior art circuit described (Fig. 2, not shown), when an ultrasonic signal is received at (17) it switches on a transistor (20) which operates a relay 23 controlling a tuning motor 11.