LeCroy AP034 Instruction Manual page 45

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12. Set the oscilloscope to display channel 1 only, set the trigger
source to channel 1, and set the channel 1 vertical scale
factor as needed to measure the amplitude of the displayed
waveform. Adjust the trigger level as necessary for a stable
display. This is the common mode signal. Turn on Math
Channel A. Press MATH SETUP, then REDEFINE A. Set the
A Math type to Average, Avg Type to Continuous, with
1:15 weighting, of channel 1. Turn off the trace 1 display.
The amplitude of the Common Mode
signal should be relatively small. If the
output waveform appears to be a 1 Volt
square wave, check that the Common
Mode
connector of the AP033/AP034 Calibration
Fixture is being used and not the
Differential Drive 50 ohm Termination
connector.
13. Measure the peak-to-peak output amplitude of the AP034.
Record the reading to two-digit resolution (xx mV) as
"Common Mode Signal at 100 MHz" in the Test Record.
14. Calculate the Common Mode Rejection Ratio (CMRR) at
100 MHz by dividing 2,000 mV by the measured Common
Mode Signal recorded in step B-14 (direct reciprocal of the
Common Mode Gain). Record the result to two-digit
resolution (xx:1) in the Test Record.
15. Verify that the CMRR at 100 MHz is greater than 18:1
(25 dB).
16. Turn off the high frequency sine wave generator RF output,
and disconnect the output cables.
ISSUED: January 2000
Note
Drive 50 ohm Termination
²