Giga-tronics Series 12000A, Руководство по эксплуатации

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Series 12000A Microwave Synthesizers
4-18 Publication 31231, Rev. J, October 2003
5. Adjust the time base of the digital scope to 1 second for the entire span of the X axis (100 mSec
typical). Set the vertical scale to 100 mV per division.
6. Pulse the generator to initiate the RF sweep.
Repeat the sweep several times. The output of the Delay Discriminator should not vary from one sweep
to another. Review the waveform and identify the nulls where the voltage transitions through the nulls
are steeper and linear for a ±50 mV range above and below the null. Perform the FM modulation tests at
these frequency nulls.
For certain frequencies, which may be identified by experiment, the mixer will produce a DC voltage
near zero. The number of null frequencies can be increased by making the delay lines longer in absolute
terms or by increasing the ratio between their lengths. If the output becomes frequency modulated, the
mixer output voltage will change, and the voltage variation will be proportional to FM deviation.
The polarity of the voltage change may be either directly or inversely related to the direction of
frequency deviation. When voltage levels have been established for different frequencies, the mixer
output can be monitored on an oscilloscope to provide a continuous display of FM deviation.
4.4.2.4 Procedure
1. Connect the FM test fixture to the RF OUT connector of the 12000A as shown in Figure 4-7.
Monitor the mixer output with the oscilloscope. Set the 12000A to any null frequency
between 4.0 and 7.99 GHz (that is, at a frequency where the mixer output voltage is zero); +10
dBm out, no modulation.
2. Establish the voltage at 1 MHz above and 1 MHz below the null frequency. Adjust the
oscilloscope gain and the 12000A output power level (near +5 dBm) to place the null point at
the center of the screen and the 1 MHz deviation points at 3 divisions above and 3 divisions
below the null point.
3. Set the 12000A to Narrow EXT FM with 1 MHz deviation. Connect the function generator,
set to a 100 kHz rate SINE wave, 1 V
P-P
. Verify that the waveform is 6 divisions peak-to-peak.
4. Adjust the 12000A FM deviation for exactly a six division peak-to-peak display. Vary the
function generator from 10 Hz to 1 MHz and verify that the display remains between five and
seven divisions peak-to-peak.
5. Vary the function generator from 1 MHz to 8 MHz and verify that the display remains between
4 and 8 divisions.
6. Establish the voltage at 10 MHz above and below the null frequency. Adjust the oscilloscope
gain and the 12000A output power level (near +5 dBm) to place the null point at the center of
the screen and the 10 MHz deviation points at 3 divisions above and 3 divisions below the null
point (terminate the Mixer output in 50
Ω
).
7. Set the 12000A to Wide EXT FM with 10 MHz deviation. Set the function generator to
100 kHz. Verify that the waveform is 6 divisions peak-to-peak.
8. Adjust the 12000A FM deviation for exactly a 6-division peak-to-peak display. Vary the
function generator from 100 Hz to 1 MHz and verify that the display remains between 4.7 and
7.3 divisions.
9. Vary the function generator from 1 MHz to 8 MHz and verify that the display remains between
4 and 8 divisions.