Simultaneous Signal Detection for IFM (Instantaneous Frequency Measurement) Receivers by Detecting Intermodulation Products.

Abstract : An apparatus for use in conjunction with an instantaneous frequency measurement (IFM) receiver, for detecting the presence of two or more RF pulse signals, differing in frequency, between the onset of the first RF signal pulse and the completion of the frequency encode strobe. A low pass filter branching off from the output of the limiting amplifier of the IFM receiver will allow passage of only the low frequency intermodulation products formed from the presence of simultaneous signals. These intermodulation products are then detected and sampled during the time period of interest with a flag set is simultaneous pulses are present. This flag, which indicates to the receiver that the data associated with the received pulse may contain erroneous information, is maintained until reset by the onset of a succeeding RF pulse. (Author)