Description - HP 37717C Calibration Manual

Performance Tests
Transmitted Jitter/Wander Amplitude Accuracy (Option A3K [A3Q])

Description

To check the accuracy of the internal jitter generator, a signal is output from the HP
37717C to a Spectrum Analyzer. The signal can be at one of the PDH rates of
2 Mb/s, 8 Mb/s, 34 Mb/s or 140 Mb/s from the PDH TX module or at 155 Mb/s
from the SDH module. At each of the rates, jitter is added to the signal until Bessel
Null points are observed on the Spectrum Analyzer. The jitter amplitudes required to
obtain these Bessel Nulls are checked to ensure they are within the specified limits.
For high levels of jitter amplitude at 2 Mb/s and 155 Mb/s, it is difficult to measure
Bessel Null points accurately on the Spectrum Analyzer. To measure Bessel Null
points at high jitter amplitudes, a Modulation Analyzer is used. The Modulation
Analyzer demodulates the jitter from the carrier and converts the jitter amplitude to
frequency deviation. The frequency deviation result is based upon the level of jitter
amplitude and the modulating frequency. Jitter generation at 622 Mb/s is a function
of the HP 37717C firmware and is based on jitter generation at 155 Mb/s and is not
tested in this performance test.
For external jitter generation, a modulating signal is input from the synthesizer at the
MOD input of the A3K module. The amplitude of the modulating signal is increased
until a Bessel Null is observed on the Spectrum Analyzer. The modulating signal
level is checked on the Oscilloscope to ensure it is within the specified limits.
To check Wander generation, an external reference 2 Mb/s clock is input to the 2M
REF IN port on the Jitter TX module of the HP 37717C under test and to the 2M
REF IN port on the Jitter RX module of the reference HP 37717C. Low frequency
Wander is added to the 2 Mb/s data which is output from the PDH OUT port and
compared with the 2 Mb/s reference clock to allow Wander measurements to be
made. Wander generation at 155 Mb/s and 622 Mb/s is a function of the HP 37717C
firmware and is based on jitter generation at 2 Mb/s and is therefore not tested in
this performance test.
3-134