Keysight Technologies N9040B UXA Signal Analyzer Service Guide 153
RF Section Troubleshooting (RF/Microwave Analyzers)
Troubleshooting
Second LO Level Verification
The second LO signal comes from the A16 Reference Assembly and is only
used in Low Band. The second LO signal can be measured by removing the
W18 semi-rigid cable from A16J702. Connect the functioning spectrum
analyzer to A16J702 connector. This signal goes to A13A1J1 via the W18
cable. Expected signal is 4800 MHz at +10 dBm when a low loss test cable is
used and with the measuring spectrum analyzer input attenuator set to at least
20 dB to prevent overload.
Figure 4-5 A16
First LO Level Verification
The first LO is the A20 YTO assembly. The first LO is phased locked by the A14
Synthesizer assembly.
To assure the first LO is tuned to the correct frequency and power, measure the
A13 Front End assembly at A13A1J3 when the analyzer center frequency is
50 MHz. This test port is chosen because removing cable W19 will not cause
the analyzer LO phase lock loop to unlock, which would affect the LO
frequency measurement. Analyzer settings should be FREQ (Channel), Center
Frequency, 50 MHz, Span, Zero Span, System, Alignments, Auto Align Off.
The LO signal should measure 5172.5 MHz at 0 dBm ± 3 dB.
If the signal level is incorrect, measure the signal coming from the A20 YTO. In
order to measure this signal and avoid an LO Unlock, you will need to install a
power splitter. Remove the W20 cable that attaches to A14J2. Connect the
input of the splitter to W20 cable using a sma (m) to sma (f) elbow. Connect
one arm of the splitter to where the W20 cable was connected. You might want
to use a short flexible semi-rigid cable. Connect the measuring spectrum
analyzer to the other arm of the splitter. Add the loss through the splitter arm
which is 6 dB for the Keysight 11667B splitter.
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