
Model 8640B
TM 9-4935-601-14-7&P
PERFORMANCE TESTS
4-24. OUTPUT LEVEL ACCURACY TEST (Complete) (Cont'd)
4. Disconnect power meter and sensor from generator. Connect test generator's RF OUTPUT to the step
attenuator as shown in Figure 4-11. Do not change any of the test generator's control settings (particularly the
OUTPUT LEVEL vernier).
5. Set reference signal generator for 515 MHz signal (with no AM) at +10 dBm. Set its modulation controls for
external FM (dc) and 640 kHz peak deviation (FM vernier at maximum).
6. Set the RF attenuator to 50 dB and the IF attenuator to 40 dB.
7. Connect spectrum analyzer to tracking generator. Set analyzer's center frequency controls to 3 MHz with the
tuning stabilizer on; set resolution bandwidth to 10 Hz, span width per division (scan width) to 5 kHz, and input
attenuation to 10 dB. Set the display controls for a linear display with 0.1 mV/div; set display smoothing (video
filter) to 100 Hz and set the tracking generator for 0 dBm output.
8. Set oscilloscope for dc input coupling, vertical to 5 mV/div, and horizontal to 0.5 ms/div.
9. Set digital voltmeter's noise filter to maximum filtering, range to 10OV, and function to dc.
NOTE
The noise filter between the analyzer and the DVM can be used instead of, or with, the DVM's
noise filter whenever the DVM's reading is obscured by noise. To use this filter, switch it off (if it
is on) for approximately two seconds to allow the capacitor to charge, then switch it on; wait
approximately 30 seconds to allow the filter to reach the average value of the signal then take the
reading.
10. Phase lock the system by tuning the reference signal generator's frequency to center the 3 MHz IF signal on
analyzer's display. Set analyzer's span width per division to zero, then tune reference signal generator to
indicate phase lock on the oscilloscope (the signal will peak, then become 0 Vdc when phase lock is reached).
NOTE
Care must be taken to ensure that all measurements are taken during phase lock. Also, the
tracking generator's tracking adjustment should be periodically checked to ensure that the trace
is peaked on the analyzer.
11. Adjust analyzer's display sensitivity controls for a -500 mVdc reading on the DVM. Measure the accuracy of test
Signal Generator's output using IF substitution by switching the OUTPUT LEVEL switch in 10 dB steps while
switching the IF attenuator (the calibrated 10 dB step attenuator). The DVM should read -500 mVdc ±0.5 dB. If
necessary, use test generator's OUTPUT LEVEL vernier to reset panel meter to +3 dB.
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