| 摘要 |
A mechanical radio receiver tuner with microphonics elimination circuitry is disclosed. During a mechanical tuning mode, the mechanical position of a movable tuning element provides an associated adjustable reactance which determines a control voltage for controlling the output of a voltage controlled oscillator (VCO) that serves as the local oscillator for a superheterodyne radio receiver. After initially selecting a channel frequency by adjusting the output of the VCO with the mechanically movable tuning element in the tuning mode, a switch means disconnects the movable tuning element from operative control of the local oscillator frequency and implements a locked tuning mode by providing the VCO with a control voltage related to the difference between the frequency of the output signal of a mixer stage and the center frequency of a fixed tuned narrow passband IF stage that follows the mixer. Preferably, this control voltage for the locked tuning mode is provided by a phase locked loop. When substantial changes in the reactance provided by the movable tuning element are sensed, the switching circuit reimplements the tuning mode so that the position of the mechanically movable element will once again control the output of the local oscillator. In this manner, minor changes in the mechanical position of the movable tuning element during the locked tuning mode have no effect on receiver tuning and therefore microphonics are substantially eliminated. |
