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14-4
Block Diagram Theory of Operation
Block Diagram 1
Block Diagram 1
RF Analyzer
Audio Analyzer
Spectrum Analyzer
A23 Input
A24 High Power Attenuator
The A23 Input assembly is both the input for the RF Analyzer section and the final output
from the RF Generator section. Additional information on how the A23 Input assembly is
used in the signal generator is covered in the Block Diagram 2 discussion.
The RF input signal is input to the HP/Agilent 8922 using either the RF IN/OUT
connector (for high power applications > 20 dBm) or using the AUX RF IN connector for
lower power input signals. The input signal on the front panel RF IN/OUT connector is
first sent to the A24 High Power Attenuator. This attenuates the signal by approximately
14 dB (8 dB on the HP/Agilent 8922F,H,M,S) where it can be directly used by the A23
Input assembly.
The A23 Input assembly has an RF power detector that converts the power on the RF IN/
OUT connector to a dc voltage. This dc signal is sent to the A19 Measurement assembly
where it is measured. These dc signals are sent to the A19 Measurement assembly using
the det_lo and det_hi inputs to the A19 Measurement assembly. The det_lo signal is lower
sensitivity (for the highest power signals) and det_hi is high sensitivity (for lower power
signals). Accurate RF power measurement can only be made using the RF IN/OUT
connector on the HP/Agilent 8922. These circuits are used to measure both CW and
Pulsed RF power. For accurate RF power measurements it is necessary to zero the power
meter and enter the frequency of the RF input signal. These two functions will cause the
power meter to use the proper correction factors to compensate for temperature changes
and frequency losses.
After the power detector, the RF IN/OUT connector is routed to a power splitter and then
an RF switch. This switch selects between the RF IN/OUT signal or the AUX RF IN
signal.
Selectable input attenuators in the A23 Input assembly are switched in and out, manually
or automatically. This keeps the input level within a range that works best for the mixers,
IF amplifiers, and detector in the remainder of the HP/Agilent 8922. Filters are
automatically switched in to remove images and other interfering signals. The frequency
ranges of the 4 different filters are shown on Block Diagram 1.
The A23 Input assembly contains a voltage multiplexer (mux) to route internal diagnostic
voltages to the A19 Measurement assembly. Diagnostics individually check that all the
input attenuator switches provide attenuation, although the accuracy of this measurement