| 摘要 |
<p>A circuit of a tuning device for tuning a radio transceiver, the circuit comprising a variable impedance device (14), which consists of a pair of variable resistors having an open circuit between their tracks, the 'wiper arm' (14a) of which is connected to a voltage controlled oscillator (VCO) (15). The voltage controlled oscillator may suitably comprise a CMOS 4046 integrated circuit. The voltage controlled oscillator outputs a stream of pulses, having in this case a 1:1 mark: space ratio, to the transceiver units micro-computer (not shown). At the centre point of the tracks of the variable impedance device (14) there is a null position corresponding to an open circuit. As the user turns a dial this centre position is indicated by a notch. As the wiper arm is moved from the centre position towards either extent, the value of the voltage at the VCO terminal (15a) increases. Because of this the rate of production of pulses, i.e. the frequency of the pulse stream output by the VCO (15), increases accordingly. Each pulse represents an increment or decrement of the frequency to which the radio transceiver (not shown) is tuned.</p> |
