Importance

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Abstract

This disclosure relates to electronic devices, such as a television receiver, whose bandwidth is automatically reduced when the signal-to-noise ratio of the incoming signals becomes lower. Two circuits respectively sample the received video signals and the noise. The outputs of these two circuits feed a divider which divides one output by the other. A tuned filter (which follows an IF stage of the television receiver), which varies its bandwidth according to a control voltage fed to it receives the varying output voltage of said divider. The video and noise signals, which are fed to the divider, are both derived from the sync signal of the television receiver. Timing circuits control the operation of the system. One of these circuits distinguishes the sync signals from the equalizing pulses and eliminates the latter thereby reducing the error in the noise measurements. Another timing circuit eliminates signals, that occur while video-intelligence is occurring, from entering into the signal-to-noise ratio determination. The system will perform for television signals in which the baseband signals satisfy the following: 1. The video information is in analog form. 2. Two fixed levels are multiplexed with the video and are such that the difference level is a known function of the video level. In the case of a National Television System Committee (NTSC) television signal such as the circuits described here are specifically designed for, the video signal is in analog form and the two fixed levels are the tip of the synchronizing (sync) pulses and its base level sometimes referred to as the porch. This base level is that level defined as the video blanking level.

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First Claim