HP 8753E User Manual page 281

Understanding Spur Avoidance
In the 400 MHz to 3 GHz range, where the source signal is created by heterodyning two higher
frequency oscillators, unwanted spurious mixing products from the source may be present at
the output. These spurs can become apparent in iilter measurements when filters have greater
than 80 dB rejection.
Spur avoidance slightly moves the frequency of both oscillators such that the source frequency
remains the same but the spurious mixing products shift out of the measurement receiver
range. The calculation of the exact frequency points where the shifting must occur (stored
Optimizing Measurement Results 5-59