Agilent Technologies 86038B User Manual page 116

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already exists for the chosen wavelength range and modulation
frequency, the measurement will not be repeated but the
existing data will be used in the measurement. To prevent its
use or force a new PDA calibration, the PDA Correction data can
be cleared.
Tips on Phase Dynamic Accuracy Correction
• If the PDA is performed, both swept and stepped
measurements will automatically apply it so long as the
modulation frequency is unchanged. The use of PDA
correction is recommended for all measurements but may be
omitted in cases where the loss variation of the test device
over wavelength is small and when the dispersion being
measured is very high. Some fiber measurements fit this
description.
• PDA should also be selected for measuring low values of
DGD, because small amount of PDL in the DUT and
instrument can contribute to the DGD result via the
amplitude-to-phase conversion.
• The PDA effect varies with modulation frequency, and for
this reason the phase dynamic accuracy correction is valid
only at the modulation frequency at which the PDA
calibration was performed.
There is often some advantage in attenuating the power level
seen at the receiver to reduce the need for PDA correction. The
amplitude-to-phase conversion effect is strongest at high input
power to the receiver, so if a test device has little attenuation,
limiting the TLS output power can reduce this effect without
significantly increasing noise. Turning off the PDA corrections
speed up normalization, but would seldom improve the accuracy
of the measurement. For example, one of the higher slope
regions of PDA correction at 2 GHz modulation frequency can
cause GD errors of 380 fs/dB when PDA corrections are off.
Similarly, at 10 MHz modulation frequency, GD errors of 18
ps/dB can result when PDA corrections are off. In order to
prevent measured PDA correction data from being used in a
measurement, the results should be cleared with the control
described below.
Agilent 86038B Photonic Dispersion and Loss Analyzer, Second Edition