SFRA45 User Manual
9-3
offset gain = measured dB – offset dB
The filtering is applied to the real and quadrature
components individually, rather than the derived
magnitude and phase values. This gives superior results as
any noise contribution to the components would have
random phase and therefore would be reduced by filtering.
The instrument can operate either in real time mode at a
single frequency where the gain and phase are filtered and
updated on the display, or it can sweep a range of
frequencies and present the results as a table or graphs of
gain and phase.
The frequency points to be measured are specified with
three parameters:
number of steps
start frequency
end frequency
The Instrument computes a multiplying factor that it
applies to the start frequency for the specified number of
steps. Note that due to compound multiplication it is
unlikely that the end frequency will be exactly that
programmed. The frequency sweep is initiated by the
START key, and when completed the data can be viewed
as a table or graphs.
Following a sweep on a control loop, the gain and phase
margins can be computed and displayed on the graph.
The window over which the measurements are computed
is adjusted to give an integral number of cycles of the
input waveform. In real time mode the results from each
window are passed through a digital filter equivalent to a
first-order RC low pass filter; in sweep mode, each result
