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STANDARD RESPONSE INDICATOR. SOME INVESTIGATIONS INTO A DEVICE FOR DETERMINING THE MINIMUM VISIBLE SIGNAL OF A RECEIVER,
ROME AIR DEVELOPMENT CENTER GRIFFISS AFB N Y
The Standard Response Indicators SRI basic function is to establish a threshold level and to provide an output signal whenever the threshold level is exceeded. Threshold detection is based on making a decision of target or no target at a certain level in the output of a receiver. For visual minimum visual signals MVS, the detection process is complicated by the addition of random noise to the desired signal. The averaging of this random noise by the repetitive sweep of the oscilloscope and the slow response time of the eye tend to increase and distort the average noise level. The increase in apparent noise level must be overcome by the desired signal in order to become visible to the operator. The SRI eliminates the problem of decision making based on an arbitrary reference level set by the operator. The decision of the SRI is based upon the detection of noise pulses exceeding a threshold voltage level in a given period of time. This eliminates most of the effects of random high-level noise spikes present in the receiver output. A large number of sample periods averaged over an interval of time remove the random effects of the noise as seen by the SRI, and an absolute indication of the presence or absence of the desired signal is obtained.