To Eliminate Receiver Spurious Responses - HP 8712ET User Manual

Dithering to Shift
Spurs
CAUTION
Activating Spur
Avoidance

To Eliminate Receiver Spurious Responses

Spurious responses are undesirable signals that result from various
internal mixing products.
The analyzer has two features to eliminate spurious responses. Both
features shift the frequency of the spur without changing the RF output
frequency. They shift the spur by changing frequencies internal to the
analyzer that mix to produce the RF frequency. The features are:
• dither
• spur avoid
Dither is usually most effective for narrow frequency span
measurements (generally <15 MHz), as explained in the following
paragraph. If dither does not eliminate visible spurs, use spur avoid
instead.
Dither shifts all spurs by a small amount once, thus it imposes no sweep
time penalty. But some spurs occurring within the measured frequency
band may not be shifted out of band, and others may be shifted in.
Therefore, dither is most effective for narrowband measurements with a
user-defined measurement calibration. To activate dithering:
1. Press
MENU
2. Make a user-defined measurement calibration. Refer to
"Calibrating for Increased Measurement Accuracy,"
procedures.
The measurement calibration must be performed with the same spur
avoid option used in the measurement or your results may be invalid.
When you activate spur avoidance, the analyzer sweeps to a point before
a spur, stops the sweep, shifts the spur, sweeps through the spur
location, then shifts the spur back and continues the sweep. The
analyzer determines which spurs need to be avoided with an algorithm
based on frequencies, number of points, sweep time, and system
bandwidth.
ET User's Guide
Spur Avoid Options
Optimizing Measurements
Reducing Trace Noise
Dither .
Chapter 6,
for calibration
5-13