| 摘要 |
1,238,608. Muting radio receivers. INTERNATIONAL STANDARD ELECTRIC CORP. 25 Nov., 1969 [29 Nov., 1968], No. 57629/69. Heading H3T. In a muting arrangement for a frequency modulation receiver, the overall response prior to a frequency discriminator is made unsymmetrical relative to the signal frequency (Figs. 2a-2d, not shown); the frequency discriminator produces a different D.C. output according to whether a signal or only noise is being received, and these two different D.C. outputs are used to mute and unmute an audio stage of the receiver. In an embodiment comprising R.F. tuned circuit 9, frequency-changer 10 and local oscillator 11, I.F. amplifier 12, limiter 13 and discriminator 14 of the integrator type, the R.F. tuned circuit 9 is mis-tuned away from the signal frequency, so that the discriminator 14 produces zero D.C. output on noise and a D.C. output voltage U D on signal. The following audio stage 15 to which discriminator 14 is direct-coupled, is then biased to cut off in the absence of a signal, but the D.C. output voltage U D biass it conductive for signal. |
