HP 83522A Service Notes page 228

Service Model 83522A
A7 Marker Assembly
The A7 Marker assembly receives the TTL "birdies" and processes them to
generate marker pulses that are centered where the RF output frequency is
exactly equal to a harmonic of the crystal oscillator, producing a mixing "null."
A digital circuit detects the time between "birdie" pulses and discriminates this
null to produce a marker pulse. This marker pulse produces 1dB markers
through the ALC circuits, and sends a pulse to the mainframe to produce Z-axis
intensity markers when enabled.
The Pulse circuits are part of the A7 Marker assembly. The Pulse circuits
essentially combine three different pulse sources: Square Mod and RF
Markers from the 83504 and Pulse Input from the plug-in rear panel. The
output (L PULSE) shuts off the RF, acting on the A17 ModulatorIMixer
through the A4 ALC assembly.
RF SECTION
The RF Section includes the microcircuits and their bias boards that produce
the actual RF output power. These components include A l l through ~ 1 9 and
DC1.
The A12 YIG (Yttrium-Iron-Garnet) Oscillator (YO) is the frequency-
controllable microwave source for the 83522A RF Plug-in. The YO's frequency
is determined by the current flowing through large electromagnetic coils inside.
This current is the result of summing and scaling operations performed by the
A6 YO Driver and A9 Reference Resistor assemblies. Due to the response-time
limitations of the main coils, a smaller coil with a much faster response, but
limited range, is used to modulate the output frequency.
The YO's 3.81 to 6.2 GHz output is fed to the A17 Modulator/Mixer. Here it is
mixed with the fixed 3.8 GHz output of the A16 Cavity Oscillator, yielding the
heterodyned output from 0.01 to 2.4 GHz. Power control and leveling is
accomplished by modulating the 3.8 GHz input before the mixer, internal to the
A1 7 ModulatorIMixer.
A14 Amplifier boosts the mixed-down low-power output from the A17 assembly.
The amplifier also serves to further remove unwanted high-frequency mixing
products. The A14A1 Amplifier Bias assembly is directly connected to the
microcircuit, has no adjustable or replaceable parts, and is not separately
replaceable.
The A15 DC Return allows DC currents to pass to ground, preventing them
from affecting other circuits.
DC1 Directional Detector serves a dual purpose. A broadband resistive bridge
couples off a portion of the R F energy, rectifies and filters it, and provides a
detected output for leveling. Another resistive tap samples the RF power for the
Marker Generation circuits.
The R F output is finally directed to the front panel R F Output connector. On
instruments with Option 004, different R F cabling takes the output to the rear
panel connector. On instruments with Option 002, the A19 R F Step Attenuator
is included, providing from 0 to 70 dB of attenuation in 10 dB steps. This
attenuated output is then routed to the front panel connector (Option 002 only)
or rear panel connector (Option 002 with Option 004).