Agilent Technologies 8590 Series Service Manual page 415

If vernier accuracy is out of tolerance
Vernier accuracy is a function of the PWR_LVL drive signal from the
A10 tracking generator control assembly and the ALC circuitry on
A3A15. The vernier accuracy is specified at 300 MHz. Since vernier
accuracy is tested using a broadband power sensor, abnormally high
spurious responses could cause the measured vernier accuracy to fail
when in fact the accuracy of the 300 MHz signal alone is within
specification.
1. Check the PWR_LVL drive signal from A10. Monitor A10J1 pin 8
with a DVM. Change the SRC POWER setting in 1 dB steps and note
the voltage at each power level setting. The voltage should change by
the same amount for each 1 dB step. If the voltage does not change
by the same amount for each 1 dB step, the fault lies on the A10
Tracking Generator Control assembly.
2. Check for abnormally high spurious outputs. Connect the RF OUT
50Ω connector to the input of another analyzer (the test analyzer).
Set the test analyzer to sweep from 300 kHz to 2.9 GHz, with a
sweeptime of 100 ms or less. Set the 8594A to sweep from 300 kHz to
2.9 GHz with a 50 second sweeptime. Press
and observe any responses on the test analyzer, ignoring the desired
output signal. If any spurious responses are greater than −20 dBc,
the vernier accuracy measurement may fail. Refer to "If
harmonic/spurious outputs are too high" in this section.
3. Check for excessive LO feedthrough. Use the LO Feedthrough
performance test in the 8590 E-Series and L-Series Spectrum
Analyzers User's Guide, but check over a center frequency range of
300 kHz to 100 MHz. The LO Feedthrough will be 3.9214 GHz
greater than the center frequency setting.
Chapter 10
Analyzer Options and Block Diagrams
Tracking Generator 8593E, 8594E, 8595E, 8596E Option 010
on the 8594A
SGL SWP
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