Agilent Technologies 8590L Service Manual page 369

Assembly Descriptions and Block Diagrams
RF and LO Section for 8592L, 8593E, 8594E, 8594L, 8594Q, 8595E, and 8596E Analyzers
The stabilizer mixes the divided sampler IF (nominally 8.25 MHz) with
the 7.5 MHz, and feeds the difference signal into the discriminator. The
discriminator output, DISCRIM, is fed back to the A7 analog interface
assembly to tune the A3A7 YTO precisely to the center frequency.
When the frequency count marker is active, the analyzer pauses at the
marked frequency and counts the first LO as described previously. The
21.4 MHz IF is then divided by four, to a nominal value of 5.35 MHz, fed
to another frequency counter input, and counted. With the second LO,
the third LO, the counted first LO, and the counted final IF all
referenced to the 10 MHz reference, the actual input signal frequency is
calculated.
A3A14 First LO Distribution Amplifier (LODA) for
Option 009 or 010
The A3A14 first LO distribution amplifier, (LODA), amplifies and levels
the first LO signal from the A3A7 YTO and distributes it to the A25A1
sampler (through attenuator AT1), A3A8 dual band mixer, and A3A15
tracking generator. The leveling control circuitry is on the A10 tracking
generator control assembly.
The LODA consists of a PIN diode attenuator, an amplifier, three
directional couplers, a buffer amplifier, and a detector. Refer to Foldouts
11-2 and 11-3. All three directional couplers are connected in series.
The main line of the directional couplers is the output to the A3A15
tracking generator assembly. The directional coupler outputs feed the
A3A6 dual-band mixer, the detector, and the buffer amplifier for driving
the A25A1 sampler.
The detector output is fed to the A10 tracking generator control
assembly. Here it is fed into a loop integrator. The reference voltage for
the loop integrator is adjustable and determines the output power of
the LODA. The gate bias adjustment is also on A10. Note that the
LODA drive circuit common is connected only to the A3A14 LODA itself
and not to any other grounds on A10.
Refer to Figure 9-5, for details about the operation of the A3A14
assembly.
A3A15 Tracking Generator for Option 010
The A3A15 tracking generator assembly consists of several smaller
circuits. The A3A15 tracking generator assembly is not
component-level repairable; a rebuilt exchange assembly is available.
The tracking generator recreates only one of the analyzer intermediate
frequencies. This minimizes isolation problems associated with a
built-in tracking generator. Each of the blocks of the A3A15 tracking
generator assembly is described below.
370 Chapter 9