| 摘要 |
A radio frequency receiver system adapted to monitor the international radio-telegraph distress frequency is disclosed. The system comprises a first receiver section coupled to a receiving antenna. Such receiver section includes an automatic gain control circuit having a relatively long time response characteristic for adjusting the sensitivity of the receiver section in accordance with the average level of received background noise, thereby to pass sudden radio frequency signals having levels above the average level of the received background noise and which are substantially unaffected by the automatic gain control circuit. The passed radio frequency signals are fed to a second receiver section. Such second receiver section includes an automatic gain control circuit which is responsive to the average level of the received background noise level in the absence of a sudden strong signal, and which is, in the presence of a sudden strong signal, responsive to the level of such sudden strong signal. The automatic gain control circuit, in response to the sudden strong signal, has a relatively fast time response characteristic.
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