HP 8924E, Сборка

Страница: 147 / 640

147
Chapter 4, Periodic Adjustments
Introduction
N:\mkt\MANUALS\HP8924C\ALR\per_adj.fb
CDMA_CAL Routines
I/Q Modulator
The four DACs on the IQ Modulator assembly are adjusted to minimize the gain/
quadrature spurs (GQS) and the origin offset spurs (OOS) that are present in IQ
modulation. Twelve adjustments are made between 500 to 1000 MHz. At each
frequency, the Phase Quadrature DAC and the I Gain DAC are adjusted to
minimize the gain/quadrature spur first, and then the I Offset DAC and the Q
Offset DAC are adjusted to minimize the origin offset spur. By reducing spurs,
carrier feed-through (caused by OOS) and modulation distortion (caused by GQS)
are reduced, increasing the Rho measurement quality.
Receiver Mixer
The mixer’s loss is characterized at several points from 0.4 to 1010 MHz to
improve the level accuracy of the Spectrum Analyzer by
≥
20%. During the
procedure, the Spectrum Analyzer’s self-calibration signal is removed and the RF
Analyzer’s power meter is zeroed. Signal level at each frequency point is
measured by the Spectrum Analyzer and RF Analyzer; calibration data is
calculated using the difference in their measurements.
Attenuator
The attenuators loss is characterized from 0 to -35 dBm in 5 dB steps. Calibration
factors are generated at 31 frequencies from.4 to 1010 MHz. The level at -40 dBm
is used as the reference to calculate the calibration factors for the other attenuator
settings. The -40 dBm setting uses 20 dB attenuators at the input and output of the
attenuator section, affecting SWR from -40 dBm and below. Using
-40 dBm as the reference helps stabilize SWR at these lower levels. A 6 inch BNC
cable and a 3 dB pad are required for this routine.
Generic Cable
Cable losses between the Input and Output sections are measured to generate
calibration factors to compensate. Calibration factors are generated at 31
frequencies from 0.4 to 1010 MHz, at a level of -40 dBm (for best SWR). See
Attenuator above.