Abstract: A system for automatic monitoring of a communication signal in the RF or IF spectrum utilizes a superheterodyne receiver technique with a VCO to select and sweep the frequency band of interest. A first memory is used to store one band sweep as a reference for continual comparison with subsequent band sweeps. Any deviation of a subsequent band sweep by more than a predetermined tolerance level produces an alarm signal which causes the band sweep data temporarily stored in one of two buffer memories to be transferred to long-term store while the other buffer memory is switched to its store mode to assume the task of temporarily storing subsequent band sweeps. Each alarm signal alternates the roles of the two buffer memories. In a second embodiment, the roles of the two buffer memories are switched at the end of each heterodyne receiver band sweep for display of successive band sweeps at a faster rate and for automatic long-term store of any band sweep producing an alarm.