Test Set Troubleshooting; Introduction; Theory Of Operation - Agilent Technologies 8511B Operating And Service Manual

6

Introduction

Theory of Operation

Test Set Troubleshooting

The troubleshooting strategy for the Agilent 8511B frequency converter test
set is a systematic sequence of procedures. This troubleshooting information
is used after system-level troubleshooting has pin-pointed the test set as the
problem instrument. Use the troubleshooting flowchart
page 6-4 to identify the faulty assembly. The troubleshooting flowchart is
keyed to numbered, individual troubleshooting procedures. As you progress
through the flowchart, perform the numbered procedure associated with each
block. Block diagrams are provided at the end of this chapter to assist in
understanding the operation of the test set.
The RF section of an 8511B frequency converter test set consists of a
voltage-tuned oscillator (VTO), a four-way power splitter and four samplers.
The frequency converter operates within the frequency range of 45 MHz to
50 GHz. Two reference (a1 and a2), and two test (b1 and b2) channels accept
RF input by way of the front panel bulkhead connectors.
The VTO/driver produces a harmonic that is 20 MHz away from the RF
source frequency. The samplers use either the fundamental or a harmonic of
the LO with the reference and test RF signals to develop a 20 MHz IF. The
IF signals are then routed to the Agilent 85102 by way of the rear panel
connector on the test set.
The LO, generated by the VTO/driver, is phase locked to the source. The
phase lock loop includes the following:
•
A3 VTO summing amplifier board
•
A14 VTO/driver
•
A12 a1 reference sampler assembly
•
A13 a2 reference sampler assembly and the 8510 network analyzer
A microprocessor on the A4 GPIB board controls the samplers, which may
be switched either on or off, depending on the parameter being measured.
The default condition is for all four samplers to be on. This insures that the
test set will be usable in the event of a failure of the A4 GPIB board or a
failure in the communication between the test set and the 8510
display/processor.
The 85102 IF detector controls the VTO/driver via the VTO summing
amplifier board. A control voltage is input to the VTO to tune to the correct
LO frequency.
Agilent 8511B Test Set Operating and Service Manual 6-1
Figure 6-2 on