M9W - Sweep Oscillator - Wavetek 3000 Instruction Manual

Section 3 .6 is deleted .
3 .7
M9W - SWEEP OSCILLATOR
The M9W is the origin of the instrument's
RF output frequency. This frequency is
generated by heterodyning the
signals
from two higher frequency voltage con-
trolled oscillators .
See Figure 3-12 .
3 .7 .1 Mixer
The narrow oscillator applies a signal
of 1198 MHz to the mixer (except in the
FM mode) .
The wide oscillator provides
between 1199 and 1718 MHz .
The differ
ence (1-520 MHz) is applied to a wide
band pre-amp and then sent to the M10W .
3 .7 .2 Wide Oscillator
The wide range of oscillation is achieved
by applying to varactor diodes
in the
tank circuit an analog signal which is
dependent upon the
setting of the fre-
quency switches on the instrument's front
panel . An additional signal is applied
to this VCO from the
phase detector in
the M34 .
This is the fine tuning signal
which locks the wide oscillator on the
proper frequency .
3 .7 .3 Narrow Oscillator
This oscillator also uses a varactor
diode so that the frequency can be vol-
tage controlled for phase locking
and
for FM operation.
The coarse modulating
signal (FM) is
applied to the varactor from the modula-
tion board (C316) . The frequency of
this oscillator is accurately controlled
by a "fine tuning" bias voltage from the
M33 phase detector . The deviation can
be controlled up to 500 kHz .
3 .7 .4 Levelers
THEORY OF OPERATION
This module contains three RF leveling
circuits as shown in the diagram .
These
maintain a constant amplitude RF over
the frequency range and with temperature
variation . The output of a peak detec-
tor is compared to a constant DC level .
Any error is amplified and applied to a
PIN diode attenuator in series with the
RF signal .
3-11