| 摘要 |
A radio receiver comprises an HF stage, an IF stage, and an LF stage connected in sequence. A first signal branch has an input connected to the IF stage and comprises in sequence a first rectifier, a first threshold circuit, a first delay stage and a switch whose output terminal controls the conduction state of a squelch switch connected in the output circuit of the LF stage. The output signal of the last-mentioned switch serves both to furnish reception-occurring and reception-pause signals and also, during normal operation, to control the squelch switch. A second signal branch has an input connected to the output of the LF stage and comprises a second rectifier and a second threshold circuit. The digital signals produced at the outputs of the first and second threshold circuits respectively indicate whether HF sensitivity and output-signal level are or are not acceptable. The delayed version of the first digital signal and the undelayed version of the second are applied to respective inputs of an AND-gate. A pulse generator responds to a reception-pause signal by enabling a third input oppthe AND-gate and also activating a broadband noise-signal generator which then applies a broadband noise signal test impulse to the input of the HF stage. |
