1 Operation and Service Guide
36 Keysight E4412A and E4413A Operating 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
dBm to -70
dBm power range with that particular sensor’s unique correction
data
applied.
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