HP 8560E Service Manual page 333

General Troubleshooting
Block Diagram Description
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 and DC block when the
spectrum analyzer turns off, providing ESD protection. (Note that the
input attenuator is not field-repairable.)
A11 YTO
A11 is a YTO (YIG-tuned oscillator). YIG (yttrium-iron-garnet) is a
ferro-magnetic material which is polished into a small sphere and
precisely oriented in a magnetic field. Changes in this magnetic field
alter the frequency generated by the YTO. Current control of the
magnetic field surrounding the YIG sphere tunes the oscillator to the
desired frequency.
A13 Second Converter
The A13 second converter down-converts the 3.9107 GHz 1st IF to a
310.7 MHz 2nd IF. The converter generates a 3.6 GHz second LO by
multiplying a 600 MHz reference. Bandpass filters remove unwanted
harmonics of the 600 MHz driving signal. First IF and 2nd LO signals
are filtered by cavity filters.
Second IF Distribution Amplifier (part of A15)
The second IF distribution amplifier (SIFA) amplifies and filters the
second IF. (Option 001 instruments provide the pre-filtered signal at
the rear panel 2ND IF OUTPUT.)
The external mixing input from the front-panel IF INPUT connector is
also directed through the SIFA. A dc bias is placed onto the IF INPUT
line for biasing external mixers.
Third Converter (part of A15)
The third converter down-converts the 310.7 MHz IF to 10.7 MHz. A
PIN-diode switch selects the LO signal used. For normal operation, a
300 MHz LO signal is used. The signal is derived from the 600 MHz
reference PLL. During signal identification (SIG ID ON) for Option 008,
the 298 MHz SIG ID oscillator is fed to the double balanced mixer on
alternate sweeps.
Flatness Compensation Amplifiers (part of A15)
The flatness compensation amplifiers amplify the output of the
double-balanced mixer. The variable gain of the amplifier (8 to 32 dB)
compensates for flatness variations within a band. Band conversion loss
is compensated by step gain amplifiers in the IF section.
332 Chapter 6