Service; Principles Of Operation - Keysight Technologies E4412A Operating And Service Manual

1 Operation and Service Guide

Service

Service instructions consist of principles of operation, troubleshooting, and
repairs.

Principles of Operation

The A1 Bulkhead assembly provides a 50 ohm load to the RF signal
applied to the power sensor. A diode assembly in the bulkhead rectifies
the applied RF to produce a dc voltage which varies with the RF power
across the 50 ohm load. Thus the voltage varies with the RF power
dissipated in the load. With maximum specified RF power (100 mW) the
dc voltage is approximately 1V.
The low- level dc voltage from the bulkhead assembly must be amplified
before it can be transferred on standard cables to the power meter. The
amplification is provided by an input amplifier assembly which consists of
a chopper (sampling gate) and an input amplifier. The chopper circuit
converts the dc voltage to an ac voltage. To do this, the chopper uses two
field effect transistors (FETs), A2Q1 and A2Q2, controlled by a 440 Hz
square wave generated by the power meter. The amplitude of the sampling
gate output (drain of A2Q1, source of A2Q2) is a 440 Hz square wave
which varies with the RF power input. The 440 Hz ac output is applied to
the input amplifier A2Q3 which provides the input to the first amplifier
stage in the power meter.
The E44XX- Series power meter automatically detects when an E44XX
Series power sensor is connected and downloads the correction data from
the sensor's EEPROM. This configures the power meter to operate over the
+20
unique correction
20
dBm to 70 dBm power range with that particular sensor's
-
data applied.
E4412A and E4413A Operating and Service Guide
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