If Bandwidth Reduction - Agilent Technologies 8753ET User Manual

IF Bandwidth Reduction

IF bandwidth reduction lowers the noise floor by digitally reducing the receiver input
bandwidth. It works in all ratio and non-ratio modes. It has an advantage over averaging
as it reliably filters out unwanted responses such as spurs, odd harmonics, higher
frequency spectral noise, and line-related noise. Sweep-to-sweep averaging, however, is
better at filtering out very low frequency noise. A tenfold reduction in IF bandwidth lowers
the measurement noise floor by about 10 dB. Bandwidths less than 300 Hz provide better
harmonic rejection than higher bandwidths.
Another difference between sweep-to-sweep averaging and variable IF bandwidth is the
sweep time. Averaging displays the first complete trace faster but takes several sweeps to
reach a fully averaged trace. IF bandwidth reduction lowers the noise floor in one sweep,
but the sweep time may be slower. The difference in noise floor between a trace measured
with a 3000 Hz IF bandwidth and with a 10 Hz IF bandwidth is illustrated by
Figure 7-20 IF Bandwidth Reduction
NOTE Hints
Another capability that can be used for effective noise reduction is the marker
statistics function, which computes the average value of part or all of the
formatted trace.
If your instrument is equipped with Option 014 (High Power System),
another way of increasing dynamic range is to increase the input power to the
test device using a booster amplifier.
Operating Concepts
Noise Reduction Techniques
Figure 7-20.
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