User Manual

Noise
When measuring low amplitude, low frequency sinewaves noise will cause variations in the
displayed result at each display update. Users should make every effort to maximise the
amplitude of the signal presented to the input. The internal noise of the instrument is random, with
a significant low frequency (1/f) element. Selecting a longer gate time will reduce the effect of this
noise, and allow the user to see the extremes of the variation and establish an approximate
average. This method may be less effective on signals with externally induced intermittent or non-
random noise (such as supply frequency interference).
Signal level
In general it is obvious from the variations of the display value that a signal is too small for
reliable counting, but on the B input at high frequencies (especially over 2GHz) the effect of
insufficient signal can be very subtle. A signal 2 or 3dB below the true threshold might only show
an error in the eighth digit in a consistent way that is not obviously detectable; for true accuracy
users are recommended to ensure that the signal level meets the published specification even
though the instrument is typically notably more sensitive.
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