HP 8924C Assembly page 457

Section Details
RF Input/Output
Section
N:\mkt\MANUALS\HP8924C\ALR\blkdia.fb
RF Frequency Measurement
The A5 Input assembly pre-scales the RF input frequency and sends it to the A37
Measurement assembly where it is counted. This measurement is used to
automatically tune the local oscillator (LO) and to select the input RF filters. The
IF is also counted by the A37 Measurement assembly via the A30 Receiver
assembly. The A16 Host Controller calculates the RF frequency from the IF
frequency measurement by taking into account the LO frequency. Accuracy is
determined by the counter clock on the A27 Reference assembly (which is derived
from the 10 MHz reference from the A29 CMDA Reference).
RF Power Measurement
The A5 Input assembly's power splitter has one port terminated by a 50
with a diode peak detector across it and a temperature sensor near it. The output of
the diode detector is sent to the A37 Measurement assembly where it is measured.
The A16 Host Controller converts the measured value to RF power and displays
it.
A temperature sensor detects the presence of too much power at the RF IN/OUT
connector. The output of the sensor is a DC voltage proportional to RF power.
This voltage is measured by the A37 Measurement assembly, and the value is
compared to a reference limit by the A16 Host Controller. The Controller displays
an overpower message if the voltage goes above the limit. The temperature sensor
is also used to temperature-compensate the RF power measurement.
Accuracy is ensured using factory-generated calibration data stored in EEPROM.
Unlike the level-control calibration data for the RF Generator, the calibration data
is mathematically applied to the measurement results by the A16 Host Controller.
The following assemblies have calibration data which affects RF power
measurement:
• A4 Attenuator
• A5 Input
• A37 Measurement
Chapter 11, Block Diagrams
Section Details
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