Pulse-counting technique enhances receiver sensitivity

A method is outlined combining a heterodyne receiver and an electronic counter that permits the detection of weak microwave signals at levels below the noise floor of a spectrum analyzer. Faint input signals plus noise are considered as a pseudorandom process of Gaussian distribution so that the video output voltage can be represented by a random process with Raleigh distribution. An electronic counter with the properly adjusted threshold voltage can be used to count the pulses of the video output signal, and the pulses when the faint input signal is on are different from the number of pulses when it is off. The usefulness of video pulse-counting techniques is demonstrated experimentally with an RF signal generator and a spectrum analyzer which simulates the microwave receiver. The present method is of value in enhancing the sensitivity of heterodyne receiver systems when they are used at power levels below the system sensitivity.