Agilent Technologies 8564EC, Service Manual

Page: 273 / 512

354 Chapter 7
General Troubleshooting
Block Diagram Description
A7 LOMA
The A7 LOMA (LO multiplier/amplifier) levels the output of the
A11 YTO and distributes the YTO fundamental frequency to the front
panel 1ST LO OUTPUT, A8 low band mixer, A10 RYTHM, and
A15U100 sampler. It also doubles the YTO frequency and levels this
signal for use by the A12 SBTX. The leveling circuitry is on the A14
frequency control assembly.
A8 Low Band Mixer
A8 low band mixer is dc-coupled and contains a limiter.
The high-band mixing is done in either the A10 YIG-tuned
filter/mixer or the A12 SBTX. PIN diode switches in A10 and A12 direct
the RF input to the appropriate mixer. A PIN diode switch in A7 LOMA
directs the 1st LO to the appropriate mixer. Power for the LO and RF
amplifiers is provided via W15 from A14.
A9 Input Attenuator
The attenuator is a 50
Ω
precision, coaxial step attenuator. Attenuation
in 10 dB steps from 0 dB to 70 dB is accomplished by switching the
signal path through one or more of the three resistive pads. The
attenuator automatically sets to 70 dB when the spectrum analyzer
turns off, providing ESD protection. (Note that the input attenuator is
not field-repairable.)
A10 YIG-Tuned Filter/Mixer
The YIG-tuned filter/mixer (RYTHM) is a combination of an RF switch,
a microwave (2.9 GHz to 26.8 GHz) mixer, and a tracking preselector.
The PIN diode switch directs the RF input to the appropriate mixer in
the A10 RYTHM assembly or A8 low band mixer.
The tracking preselector is a YIG-tuned filter. It functions as a tunable
bandpass filter for microwave signals. Coarse frequency control
originates from slope and offset DACs located on the A14 frequency
control assembly. (Slope and offset DAC values are loaded into
EEROM.)