580 Chapter11
Synthesizer Section
Sweep Generator Circuit
Press PRESET and set the spectrum analyzer to the following
settings:
18.Using an oscilloscope, check that the sweep ramp at A14U320 pin 6
sweeps linearly from 0 to +10 Volts in 50 ms, then resets to 0 Volts.
19.Change the sweep time to 10 seconds and check that the sweep ramp
(U320 pin 6) sweeps linearly from 0 to +10 Volts in 10 seconds, then
resets to 0 Volts.
20.Change the spectrum analyzer settings as follows:
Span .................................................................................0Hz
Sweep time ................................................................... 10ms
21.Check that the ramp (U320 pin 6) sweeps linearly from 0 to
+10 Volts in 10 ms, then resets to 0 Volts.
22.If the any of the sweep times were not within specification or the
sweep ramp appeared to be non-linear in the preceding steps,
proceed with the following checks:
23.Connect the negative lead of a voltmeter to A14Q3 pin 8 and connect
the positive lead to A14U312 pin 1 to check the temperature sensor
(U312).
24.The voltage at pin 1 should be 10 mV/°C times the temperature of
the A14 frequency control assembly. (For example, if the ambient
temperature is approximately 20°C, and the A14 frequency control
assembly is 10°C warmer, the actual temperature of the A14
assembly is 30°C and U312 pin 1 should measure 300 mV.)
25.To check the temperature-dependent offset voltage generator,
connect the positive lead of the voltmeter A14Q3 pin 6. The
voltmeter should read −600 mV ±150 mV.
26.To check the DAC buffer, A14U334A, connect the positive lead of the
voltmeter to A14U334 pin 2. The voltmeter should read the same
voltage measured at A14Q3 pin 6, within 2 mV. (The same voltage
should be present at U334 pin 3.)
27.To check the buffered DAC, press
PRESET and set the spectrum
analyzer as follows:
Center frequency .................................................. 300MHz
Span ...................................................................... 100MHz
Sweep time .................................................................50ms
28.Connect the positive lead of the voltmeter to A14U334 pin 1. The
voltmeter should read the same voltage measured at U334 pin 2,
within 2 mV.
29.Change the spectrum analyzer sweep time to 2000 seconds. The
voltage at A14U334 pin 1 should increase by 275 mV ±20 mV
(compared to the voltage measured in step 12).
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