Noise blanking system for an AM radio receiver

DETAILED DESCRIPTION To a conventional AM radio receiver there is added a preliminary blanking means and an audio blanking means.
In one particular aspect of the invention, the preliminary blanking means is connected to a detection point and to another point, the RF blanking point that is either coincident with or downstream of the detection point in the AM-modulated-signal path of the receiver.
In another particular aspect of the invention, the preliminary blanking means includes a separate antenna for detecting the noise impulse.
the preliminary blanking means is for generating a preliminary blanking pulse of predetermined fixed duration and for blanking the signal in the AM-modulated-signal path for said duration at the RF blanking point when a noise pulse is detected.
The audio blanking means is connected to a sensing point in the AM-modulated-signal path, that may be the above-mentioned detection point, or to the separate antenna, and is connected in the audio-signal path of the receiver for interrupting the audio-signal path for a period of from 2 to 5 times that of the preliminary blanking pulse duration.
A sample and hold circuit means connected downstream of the audio blanking point of the audio-signal path is for sampling and holding the voltage constant there during the above-noted period of audio-signal-path interruption.
This has the effect of smoothing the interrupted portion of the audio signal.
In a conventional radio receiver the audio bandwidth is limited and determined by the bandwidth of the radio-frequency selective circuits in the preceeding AM-modulated-circuit path.
And in that path the most narrow and controlling bandwidth is commonly found in the IF section.
Thus the least width of a noise pulse that occurs in the audio section in response to an impulse of amplitude modulation at the input of the IF section is inversely related to the bandwidth of the IF section.
However, this invention recognized that the width of a disturbance that occurs in the audio section in response to RF blanking and the resulting square pulse of amplitude modulation in the input of the IF section will always be twice or a little more than twice the width of the square pulse of amplitude modulation no matter what bandwidth the IF section may have