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Front End Cal (YIG-Tuned Filter/Mixer (RYTHM) and Frequency
Response Adjustment)
Assemblies
Adjusted
Al4 Frequency Control Assembly
Al5 RF Assembly
A10 RYTHM
Related
Performance
Tests
Displayed Average Noise Level
Frequency Response
Image, Multiple, and Out-of-Band Responses
Second Harmonic Distortion
Description
Front End Cal is an automated adjustment that performs the equivalent of two manual
adjustment procedures, Frequency Response Adjustment, and YIG-Tuned Filter/Mixer
(RYTHM) dj ta us ment. The RYTHM adjustment is performed first, followed by the frequency
response adjustment.
The RYTHM adjustment optimizes the settings of the offset and slope DACs on the Al4
Frequency Control assembly for maximum amplitude response. The offset DAC value is
optimized at a low frequency and the slope DAC value is optimized at a high frequency.
The frequency response adjustment consists of applying a signal of known amplitude at
several different frequencies to the specturm analyzer. At each frequency, the RF GAIN DAC
co&rolling the flatness compensation amplifiers is adjusted to place the displayed signal at the
same place on screen. When tuned to a frequency in a preselected band, the preselector is
centered before adjusting the RF GAIN DAC.
After both adjustments are done, the preselector slope and offset DAC values, the RF GAIN
DAC values, and the preselector peak DAC values are stored in EEROM.
Note
Front End Cal refers to the HP 8481A or 8485A power sensor as the “Channel
B Power Sensor,”
even if a single-channel power meter (such as an HP 436A or
8902A) is being used.
If an HP 8485A Power Sensor is used, it must have a calibration factor at
10 MHz. Standard HP 8485As have calibration factors down to only 50 MHz.
3-14 Frequency Response Adjustment Software