| 摘要 |
<p>Selected radio circuits are fabricated on modules which plug into a "mother" board located in the radio chassis. The circuitry included a plurality of RF front ends (including at least one AM and one FM front end), each tunable over a selected radio band by tuner circuitry. The AM front end includes a saturable core reactor whose tuning inductance varies as a function of the tuning current provided to it by a voltage-to-current converter in the tuner. Both AM and PM signals are translated by a frequency synthesizer to a common IF frequency, namely 10.7 MHz. The synthesizer employs a quarts crystal controlled oscillator feeding a phase lock loop whose frequency is varied via the tuning control. Quartz crystal filters for AM, and ceramic filters for PM provide required selectivity. As all signals are at the same IF, a common IF amplifier is employed. Further, a single phase lock loop is adapted to demodulate both AM and PM signals. The resultant demodulated signals are amplified, and tone shaped, via D. C. voltage controlled audio processor circuitry. The audio circuitry is adapted to accept auxiliary inputs, such as the output of a tape player. A digital display senses tuner status providing frequency read out. Additional provisions allow switching the display to read out tape player status, or to provide a time display from an electronic clock.</p> |
