Agilent Technologies 8590 Series Service Manual page 360

Assembly Descriptions and Block Diagrams
RF and LO Section for 8590L, 8591E, and 8591C Spectrum Analyzers
A5 Second Converter
The 2.1214 GHz first IF signal is downconverted by the A5 second
converter to a 321.4 MHz second IF. This is accomplished by mixing the
first IF signal with the 1.8 GHz second LO signal. The second LO signal
is produced by multiplying the 600 MHz signal from the A9 Third
Converter by three.
The 2.1212 GHz bandpass filter is a high Q filter that eliminates
unwanted mixing products. Its performance is due to the resonant
characteristics of three precisely machined cavities in an aluminum
block.
The 321.4 MHz matching filter is an adjustable bandpass filter that
prevents unwanted mixing products from passing on to the A9 third
converter.
A9 Third Converter
The A9 third converter performs five functions:
1. Produces the 300 MHz CAL OUT signal. The CAL OUT signal is rich
in harmonics; these are required for the
routine.
2. Provides the 600 MHz reference to the multiplier on the A5 second
converter assembly.
3. Sends a 300 MHz signal to the A25 counterlock assembly. The A25
assembly locks the 300 MHz signal to the 10 MHz frequency
reference. Note that this step applies to all 8591C, 8591E and 8590L
analyzers.
4. Converts the 321.4 MHz IF signal to the final 21.4 MHz IF signal.
• The 321.4 MHz IF signal is first amplified and filtered by the
321.4 MHz bandpass filter.
• The 600 MHz reference is divided to produce the 300 MHz third
LO.
• The filtered 321.4 MHz IF signal and the 300 MHz third LO mix
at the third mixer, a double-balanced mixer, to produce the
21.4 MHz IF.
• The 21.4 MHz IF passes through a 21.4 MHz bandpass filter, a
buffer amplifier with a nominal 19 dB of gain, and a variable IF
calibration amplifier. The variable amplifier has a gain range of
−15 to +2 dB.
360
self-calibration
CAL FREQ
Chapter 9