Agilent Technologies E8285A Manual page 134

Periodic Adjustments/Calibration
Periodic Calibration Menu Descriptions
External Modulation Path Gain
The Audio Frequency Generator Gain program should be performed
before running the External Modulation Path Gain program.
The "path" in this program runs from the external MODULATION IN connector
through the Modulation Distribution assembly, through the Monitor Select Switch,
and then through Audio Analyzer 1 to the Test Set's internal DVM. The dc source
is Audio Frequency Generator 1 through the AUDIO IN connector and an external
cable.
The goal of this procedure is to set the External Level Amplifier gain DAC (on the
Modulation Distribution assembly) to produce a gain of exactly 4 between the
MODULATION IN connector and output of the Monitor Select Switch. This
requires measuring the input and output levels, calculating the gain, changing the
DAC setting, and then repeating the process until the calculated gain equals 4.
Audio Analyzer 1 Offset
Two DC offsets are measured and downloaded as calibration factors to the Audio
Analyzer 1 assembly. These measurements are determined under the following
conditions:
• Input-select switch grounded
• AUDIO INPUT selected with return conductor grounded
Variable Frequency Notch Filter
The calibration factors for tuning the variable-frequency notch filter are
determined as follows:
The input to the filter is set to 10 evenly-spaced frequencies between 300 and
10,000 Hz. The DAC that tunes the notch filter is adjusted for best null of the tune
error voltage. From this data, three coefficients of a parabola which best fit the
tuning data are calculated using a least-squares curve fit. The coefficients are then
automatically downloaded into the Test Set's non-volatile memory.
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