Chapter 9 369
Assembly Descriptions and Block Diagrams
RF and LO Section for 8592L, 8593E, 8594E, 8594L, 8594Q, 8595E, and 8596E Analyzers
The buffered 21.4 MHz IF signal is amplified in the IF calibration
amplifier (IF Cal Amp). The gain of the calibration amplifier is
controlled by a DAC on the A7 analog interface assembly via the
REF_LVL_CAL control line. During the
CAL AMPTD routine, the gain of
the calibration amplifier is adjusted so that the reference level at
top-screen is calibrated. The amplitude reference for the routine is
provided by the −20 dBm CAL OUT signal with 10 dB of input
attenuation in band 0. Refer to “IF Power-Level Measurement” in
Chapter 5 for more information about the 21.4 MHz output from the
A9 third converter assembly.
A25 Counterlock Assembly
The A25 counterlock assembly performs four main functions:
• Phase-locks the 600 MHz SAW oscillator on the A9 third converter to
the 10 MHz reference.
• Counts the first LO frequency.
• Provides discriminator output, DISCRIM, to the A7 analog interface
assembly.
• Counts the 21.4 MHz IF.
Refer to Figure 9-5, at the end of this chapter for details about the
operation of the A25 counterlock assembly.
On the A9 third converter, the output of the 600 MHz oscillator is
divided by two and the resulting 300 MHz signal is routed to the A25
counterlock assembly. The A25 counterlock assembly divides the
300 MHz signal by 40 to generate a 7.5 MHz reference for the sampling
oscillator, stabilizer, and frequency counter. The 7.5 MHz reference and
the 10 MHz reference are divided further and compared in a
phase-frequency detector. The output of the phase-frequency detector,
VTO_TUNE, is fed back to A9 to tune the 600 MHz oscillator.
The sampling oscillator provides a 279 to 298 MHz driving signal to the
A25A1 sampler. The first LO signal is also applied to A25A1 sampler.
The first LO signal is mixed with a harmonic of the sampling oscillator
signal to generate the sampler IF. This IF is divided by 10 and fed to
one input of the frequency counter. The equation used to produce the
first LO frequency is:
Ist LO Frequency =N x F
SO
+ Sampler IF
N represents the harmonic of the sampling oscillator.
F
SO
represents the sampling oscillator frequency.
Sampler IF represents the counted sampler IF (may be negative).
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