Pat, The times I had the analyzer jump to 1 Hz were when I had the 0 (zero) Hz trace on the screen along with my signal to be measured and I had pushed the PEAK SEARCH or MKR-> function. Sometimes one can have the zero Hz trace right on the far left vertical graticule of the display and not realize it, especially when measuring low frequencies at a large span. If it happens again, disconnect the input cable RF and see if any spikes remain - you'll probably see the 0 Hz retrace line.
Hope this helps Tom Cokenias RFI/EMC Consultant
