Specifications

Chapter 6 41
Making Distortion Measurements
Identifying Analyzer Generated Distortion
Making Distortion Measurements
Step 7. To determine whether the harmonic distortion products are generated
by the analyzer, first save the trace data in trace 2 as follows:
(ESA) Press
View/Trace, Trace (2), Clear Write.
(PSA) Press
Trace/View, Trace (2), Clear Write.
Step 8. Allow trace 2 to update (minimum two sweeps), then store the data
from trace 2 and place a delta marker on the harmonic of trace 2:
Press
View.
Press
Peak Search, Marker, Delta.
The analyzer display shows the stored data in trace 2 and the measured
data in trace 1. The
∆Mkr1 amplitude reading is the difference in
amplitude between the reference and active markers.
Step 9. Increase the RF attenuation to 10 dB:
Press
AMPLITUDE Y Scale, Attenuation, 10, dB.
Notice the
∆Mkr1 amplitude reading. This is the difference in the
distortion product amplitude readings between 0 dB and 10 dB input
attenuation settings. If the
∆Mkr1 amplitude absolute value is
approximately
≥1 dB for an input attenuator change, the distortion is
being generated, at least in part, by the analyzer. In this case more
input attenuation is necessary. See Figure 6-2.
Figure 6-2 RF Attenuation of 10 dB
The
∆Mkr1 amplitude reading comes from two sources:
1) Increased input attenuation causes poorer signal-to-noise ratio. This
can cause the
∆Mkr1 to be positive.
2) The reduced contribution of the analyzer circuits to the harmonic
measurement can cause the
∆Mkr1 to be negative.
Large
∆Mkr1 measurements indicate significant measurement errors.
Set the input attenuator to minimize the absolute value of
∆Mkr1.