HP 70908A, Service Manual

Page: 233 / 335

T est 13. Residual Responses
The purpose of this verication test is to measure residual responses generated by the DUT
with no signal at the DUT RF INPUT . (The residual responses measured by this test are mixing
products of the DUT second and last LOs and the second and last IFs .)
This is a nal test.
1. Connect the equipment as shown in the test setup illustration for this procedure .
2. Set the mainframe line switch to ON.
3. Load and run T est 14. Miscellaneous Residual Responses . Refer to Chapter 2 for information
about running the software .
When performing this verication test, before measuring residual responses , the test
characterizes DUT gain, DUT input attenuator , and the calibrated spectrum analyzer input
attenuator . The characterization data later corrects the measured residual responses .
Characterizing the DUT Gain
The full microwave source provides a 300 MHz, 010 dBm , signal at the DUT RF INPUT . DUT
input attenuation is 010 dB. The local oscillator source tunes to center the response . The
calibrated spectrum analyzer stores the 21.4 MHz OUT amplitude , which is then corrected for
DUT atness . The test then calculates DUT gain: corrected 21.4 MHz amplitude minus 10 dBm
RF INPUT .
Characterizing the DUT Input Attenuator
With the DUT input attenuator set to 10 dB attenuation, the calibrated spectrum analyzer
measures the 21.4 MHz OUT amplitude . The measurement repeats with 0 dB input attenuation.
The DUT attenuator correction factor equals the second measurement minus the rst. Only the
0 to 10dB DUT input attenuator setting is of interest.
Characterizing the Calibrated Spectrum Analyzer Input Attenuator
With the calibrated spectrum analyzer input attenuator set to 10 dB, the analyzer measures
the DUT 21.4 MHz OUT amplitude . The measurement repeats with 0 dB attenuation. The
calibrated spectrum analyzer attenuation correction factor equals the second measurement
minus the rst.
Measuring Residuals
The full microwave source RF output is o. The DUT input attenuation is 0 dB . In each of the
four bands the local oscillator source tunes to known residual frequencies , and the calibrated
spectrum analyzer measures responses at the 21.4 MHz OUT . The test corrects the measurement
for DUT gain, DUT attenuation error , calibrated spectrum analyzer error , and DUT atness , and
then compares the result with test limits .
8-28 Module V erication T ests