Model 8640B
TM 9-4935-601-14-7&P
ADJUSTMENTS
5-43. RF OSCILLATOR OUTPUT POWER ADJUSTMENT (Cont'd)
6. Loosen two screws on the buffer amplifier board and slide board forward or backward until power reads +0.5 dBm
(Divider/Filter Buffer Amplifier) or -12 dBm (Counter Buffer Amplifier). (Pushing board forward will increase
power.)
7. Tighten screws and check power level across band. Power should remain within the limits of +0.5 to +4.5 dBm
(Divider/Filter Buffer Amplifier) or -12 to -2 dBm (Counter Buffer Amplifier).
8. Disconnect power sensor and connect spectrum analyzer to the buffer amplifier output.
9. Set analyzer's input attenuation to 50 dB, resolution bandwidth to 300 kHz, frequency controls to span 200 to
1200 MHz, and vertical sensitivity (reference level) controls to +10 dBm.
10. Tune oscillator across band and observe second and third harmonics, which should be more than 17 dB below
fundamental for all frequencies.
11. Re-install RF Oscillator.
12. Perform Harmonics Test (4-17), Output Level Flatness Test (4-25), Single Sideband Phase Noise Test (4-19) or
Residual FM Test (4-22), and Output Leakage Test (4-29).
5-44. FM LINEARITY ADJUSTMENT (Alternate)
REFERENCE:
Service Sheet 7.
DESCRIPTION:
The Signal Generator is modulated with a 1 kHz signal. The generator's RF output is then demodulated with an FM
discriminator and the distortion on the discriminator output is observed with a spectrum analyzer. The shaping circuits
are then adjusted for minimum distortion across the 0.5 to 1 MHz frequency range. (See paragraph 5-41 for another FM
Linearity Adjustment which should be more useful in troubleshooting FM distortion).
NOTE
The preliminary FM Adjustment (5-38) should be made before performing this adjustment.
5-39
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com