| 摘要 |
<p>1312935 Interference suppression in radio receivers PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 29 Oct 1970 [1 Nov 1969] 51447/70 Heading H4L The output of the detector 3 of a radio receiver is supplied via an emitter follower 4, field effect transistor 5 which is blocked in the presence of noise pulses, resistor R 1 and capacitor 17 to the audio-frequency stages, a capacitor C providing de-emphasis. Interference pulses d, Fig. 2 I, are selected by a detector 7 coupled to the I.F. amplifier 2, for example, as described in Specification 1,279,756, and trigger a monostable device 8 providing pulses, Fig. 2 II, to block the gate 5. These pulses are also supplied to a second mono-stable device 9 which is triggered by the trailing edge of the pulses from 8 to produce negative pulses, Fig. 2 III, which block a normally conducting field effect transistor 10. Fig, 2 IV shows the output of the gate 5, a voltage step #E occurring at the end of the cut-off period of the gate. At this time the gate 10 is blocked and a pulse of amplitude #E, Fig. 2 V, is supplied via an emitter follower 12, capacitor 16 and resistor R 2 to the de-emphasis capacitor C. It is shown that by a suitable choice of R 2 the charge on capacitor C is modified to approximate more closely to the desired signal output. A further improvement may be effected by taking the output from a tap on resistor R 2 .</p> |
