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9. Frequency Response Adjustment
9. Frequency Response Adjustment
Assembly
Adjusted
Al5 RF assembly
Related
Performance
Tests
Displayed Average Noise Level
Frequency Response
Description
A signal of the same known amplitude is applied to the spectrum analyzer at several different
frequencies. At each frequency, the DAC controlling the flatness compensation amplifiers
is adjusted to place the peak of the displayed signal at the same place on the screen. The
preselector is centered at each frequency before setting the DAC value. There are also
correction points at 2 MHz and 6 MHz, which are outside the synthesized sweeper frequency
range. The DAC values for these two points are set to a fixed offset from the DAC value at
10 MHz. The DAC values are stored in EEROM.
Automated
Procedure
Available
The frequency response adjustment requires making several measurements at more than
120 different frequencies over the spectrum analyzer frequency range.
‘Ihis
manual procedure
takes over two hours to complete. However, an automated procedure, with software, is
provided by HP. The software can allow the adjustment to be performed in less than
20 minutes. The Automated HP 85623 “Front End Cal” adjustment performs this task, and
is described in Chapter 3,
“Frequency Response Adjustment Software.”
Adjustment Procedures 2-43