HP 8560A, Service Manual

Page: 416 / 450

A10 Tracking Generator (Option
002)
Block Diagram Description
The A10 Tracking Generator consists of several smaller circuits. The A10 is not
component-level repairable; a rebuilt exchange assembly is available.
The block diagram of the tracking generator is unique in that it only recreates one of the
spectrum analyzer’s intermediate frequencies. This minimizes isolation problems associated
with a built-in tracking generator. Each of the blocks comprising the A10 Tracking Generator
is described below.
Tracking Oscillator
The tracking oscillator enables the fine adjustment of the tracking generator output frequency
to compensate for the frequency inaccuracies of the spectrum analyzer’s 10.7 MHz IF. The
tracking oscillator determines the residual FM and frequency drift of the tracking generator.
The 182.14 MHz output frequency is obtained by doubling the output of a crystal oscillator
operating at 91.07 MHz.
Upconverter
The upconverter mixes the tracking oscillator output with the buffered 600 MHz reference
from the Al5 RF Assembly. The upconverter also contains a filter to pass only the 782.14
MHz upper sideband.
Pentupler
The pentupler multiplies the 782.14 MHz signal by five to generate 3.9107 the spectrum
analyzer’s 1st IF. A dual cavity band-pass filter centered at 3.9107 eliminates all
unwanted multiples of 782.14 MHz.
Modulator
The output of the Pentupler is passed through a Modulator to adjust the power level into the
Output Mixer. The modulator is controlled by an ALC circuit on the Bias Board which is fed
by a detector in the Output Amplifier. If the detected output power is too high, the ALC will
drive the Modulator to decrease the input level into the Output Mixer, resulting in a decrease
in output power.
Coupler
The 1st LO signal from the A7 LODA is coupled off and buffered to drive the Output Mixer.
The main line of the coupler is fed to the
LO OUTPUT on the front panel. The loss
through the coupler main line is less than 2.5
Output Mixer
The 3.9107 signal from the Modulator is fed into the RF port of the Output Mixer. The
LO port of the output mixer is driven by the buffered 1st LO signal from the Coupler. The
output of the mixer is then amplified.
II-18 RF Section