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This completes a check of the 2nd LO upper DAC. A
check of the 2nd LO lower DAC follows. Perform the rest of
this step for Option 03 instruments only.
Calibration—492/492P Service Vol. 1 (SN B030000 & up)
Performance Check
u. Apply 0.2 ms markers, then center one of the markers
with the FREQUENCY while reducing FREQ SPAN/DIV to
1 kHz (change REFERENCE LEVEL as necessary).
v. Enter 5K at the controller and note the difference in
the displayed signals. Since more than two time marks may
be displayed, note the difference between the centered time-
marker and the nearest time-marker. The difference should
not exceed 0.35 division (7% of 5 kHz tune or 350 Hz).
3. Check Calibrator (frequency 100 MHz ±1.7 kHz,
output level -2 0 dBm ±0.3 dB)
a. Check the calibrator frequency by connecting a fre
quency counter (e.g., TEKTRONIX DC 508 or Hewlett-
Packard Model 5342A Digital Counter) to the 492/492P
CAL OUT connector and measure the frequency. Funda
mental frequency is 100 MHz ±1.7 kHz.
b. Three procedures for measuring output level are giv
en; vector voltmeter, power meter, and comparison method
using an accurate -20 dBm source.
1. Vector Voltmeter Method
a. Terminate the voltmeter probe with a 50 Ω
feedthrough termination and then connect the
terminated probe to the 492/492P CAL OUT
connector (Fig. 3-2).
b. Set the vector voltmeter frequency to 100 MHz.
c. Check—for an rms reading between 21.11 mV
and 22.69 mV (-2 0 dBm is 22.36 mV rms
across 50 Ω).
2. Power Meter Measurement
a. Test equipment setup is shown in Fig. 3-2.
b. Connect the power meter sensor through a
lowpass filter (>40 dB at 200 MHz to remove
harmonics of the fundamental) to the CAL OUT
connector.
NOTE
Insertion loss of the filter with pads, measured at
100 MHz, must be determined to within ±0.05 dB. To
ensure a 50 Ω match, use approximately 3 dB mini-
mum-loss matching pads (attenuator) on both sides of
the fitter.
492 Spectrum Analyzer
Method #1
Vector Voltmeter
i/C«l Out —
O a o
Φ o
• ·
Method #2
Power Meter
ffi
3 dB Pad
To
3 dB Pad
Method #2
Sensor
o
150 MHz Low Pass Filter
Fig. 3-2. Test equipment setup showing two methods that check calibrator output level.
3-10 REV AUG 1981
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