Chapter 11 611
RF Section
A10 Tracking Generator (Option 002)
frequency control assembly. Set the TRK GEN RF POWER to a level
at which the flatness is out-of-tolerance. Monitor A17J16 pin 1 with
a DVM and step the center frequency in 100 MHz increments from
100 MHz to 2.9 GHz and plot the voltage variation versus frequency.
A discontinuity in the plot near the frequency at which the flatness
is out-of-tolerance indicates a problem on the A14 frequency control
assembly.
2. Check the flatness of the 1ST LO IN signal. Perform the "1ST LO
OUTPUT Amplitude" performance test. If the test passes, the fault
is most likely in the A10 tracking generator. If the test fails, note the
center frequency setting at which the power level was
out-of-tolerance and compare against the frequency(ies) at which the
flatness was out-of-tolerance. Repeat the test with the power sensor
connected to the end of W43 nearest A10, noting the center
frequency of any out-of-tolerance power levels. The power level
should be +16.5 dBm ±2 dB.
If the power level is correct at W43 but out-of-tolerance at the 1ST
LO OUTPUT, and the center frequency setting of the
out-of-tolerance power levels is close to the frequencies at which the
output is unleveled, suspect A10.
If the power level at W43 is also out-of-tolerance, suspect either the
A7 LODA or the A11 YTO. Refer to Chapter 10, "Synthesizer
Section."
3. Check all coax cables, especially semi-rigid cables. A fault in one of
these cables can cause a very high-Q power hole.
Vernier Accuracy Out-of-Tolerance
Vernier accuracy is a function of the POWER LVL drive signal from the
A14 frequency control assembly and the ALC circuitry on A10. 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 POWER LVL drive signal from A14. Monitor A17J16 pin
1 with a DVM. Change the TRK GEN RF POWER 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 A14 frequency control assembly.
2. Check for abnormally high spurious outputs. Connect the RF OUT
50 Ω to the input of another spectrum analyzer (the "test analyzer").
Set the test analyzer to sweep from 300 kHz to 2.9 GHz, with a
sweep time of 100 msec or less. Set the HP 8560E/EC to sweep from
300 kHz to 2.9 GHz with a 50 second sweep time. Press
SGL SWP on
the HP 8560E/EC and observe any responses on the test analyzer,
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