Excessive Residual Fm; Flatness Out-Of-Tolerance - HP 8560E Service Manual

RF Section
A10 Tracking Generator (Option 002)
negative DVM lead to A17J16 pin 6. Vary the TRK GEN RF POWER
or center frequency settings, as appropriate, and plot the voltage
variation versus power level or frequency. A discontinuity in the plot
near the frequency or power level at which the output is unleveled
indicates a problem on the A14 frequency control assembly.

Excessive Residual FM

Either the tracking oscillator or the ALC circuitry could be responsible
for excessive residual FM. The residual FM should be measured on
another spectrum analyzer, such as an HP 8566A/B or HP 8568A/B,
using slope detection with the HP 8560E/EC set to zero span.
Proceed as follows to troubleshoot residual FM problems:
1. Perform the "Residual FM" performance test for the spectrum
analyzer in the HP 8560 E-Series Spectrum Analyzer Calibration
Guide. If this test passes, the 1st LO input and 600 MHz drive
signals should be correct. If the test fails, troubleshoot the
synthesizer section.
2. Monitor A14J17 pin 15 (TUNE +) with an oscilloscope. Connect the
oscilloscope probe ground lead to A14J17 pin 6. The voltage at this
point should be greater than 500 mV. If the voltage is less than 500
mV, perform the "Tracking Oscillator Range" performance test in the
HP 8560 E-Series Spectrum Analyzer Calibration Guide. If this test
fails, perform the "Tracking Oscillator Range Adjustment". If the
noise on this tune line is greater than 10 mV, troubleshoot the BITG
drive circuitry on A14.
3. Monitor the output of the tracking generator with another spectrum
analyzer. Check for high-amplitude spurious responses from 100
kHz to at least 3 GHz. If the spurious responses are too high in
amplitude, the (broadband) ALC detector may cause the ALC loop to
oscillate, generating FM sidebands. If any spurious responses are
excessively high, refer to "Harmonic/Spurious Outputs Too High" in
this chapter.
4. If no spurious responses are present or are sufficiently low enough in
amplitude to not cause a problem, suspect the tracking oscillator in
A10.

Flatness Out-of-Tolerance

The output level flatness of the tracking generator is specified at a 0
dBm output power setting. In general, most flatness problems will be a
result of a failure in the A10 tracking generator microcircuit. However,
the POWER LVL signal from the A14 frequency control assembly and
the 1ST LO IN signal from the A7 LODA can also contribute to flatness
problems.
1. Check the function of the POWER LVL signal from the A14
610 Chapter 11