Agilent Technologies 8590 Series Service Manual page 367

Assembly Descriptions and Block Diagrams
RF and LO Section for 8592L, 8593E, 8594E, 8594L, 8594Q, 8595E, and 8596E Analyzers
The LO section provides a 3.0 to 6.8214 GHz first LO, a 600 MHz
second LO, a 300 MHz third LO, a 300 MHz CAL OUT signal, and an IF
frequency counter. The counter and the local oscillators use one of two
10 MHz frequency references: the standard room temperature crystal
oscillator (RTXO) or the A22 precision frequency reference,
oven-controlled crystal oscillator (OCXO).
The 10 MHz reference phase-locks the 600 MHz oscillator on the A9
third converter. The 600 MHz signal drives the second converter and is
divided to produce the 300 MHz third LO and CAL OUT signals. A
300 MHz signal that is sent to the A25 counterlock assembly is divided
down further to produce a 7.5 MHz reference signal. This 7.5 MHz
reference is used by the stabilizer, the sampling oscillator, and
frequency counter. The phase-frequency detector is located on the A25
counterlock assembly.
The first LO output of the A3A7 YTO is fed through the A3A13 isolator
to the A3A10 directional coupler. The main output of the coupler is sent
to the A3A6 dual-band mixer (low-band mixer for the 8594E and
8594Q). The coupled output is fed through the AT1 10 dB pad to the
A25A1 sampler. The sampler mixes the first LO with a harmonic of the
sampling oscillator to generate a 60 to 100 MHz sampler IF. This value
is then divided by 10, producing a 6 to 10 MHz output.
During retrace, the YTO is locked to the selected first LO frequency.
The divided sampler IF is then counted in the frequency counter. The
YTO tune DACs on the A7 analog interface assembly are adjusted until
the counted frequency is equal to the desired frequency. In LO spans
less than or equal to 10 MHz, the divided sampler IF is also fed to a
stabilizer, which generates the DISCRIM (discriminator) signal.
DISCRIM tunes the YTO precisely to the desired first LO frequency.
When a trigger signal occurs, a sweep ramp is applied to the main coil
drivers while in LO spans greater than 10 MHz, or to the FM coil
drivers while in LO spans less than or equal to 10 MHz. During a main
coil sweep, the sampling oscillator is disconnected from the A25A1
sampler.
In frequency count mode, the first LO sweeps up to the marked signal
and pauses. The divided sampler IF is counted to calculate the actual
first LO frequency. Then the prescaled 21.4 MHz IF, nominally
5.35 MHz, is counted and the actual input frequency calculated.
Chapter 9 367