Wavetek 3000 - SECTION 3 THEORY OF OPERATION; Introduction to Theory of Operation; Overall Block Diagram; Basic Signal Generator

3.1 INTRODUCTION
Section 3 .2 presents a block
diagram
analysis to enable the reader
to get a
brief overall view of the
operation of
the instrument .
Sections 3 .3 - 3 .15
contain more detailed
descriptions of
each subassembly .
For actual wiring of the
chassis and
subassemblies, refer
to the schematics
in Section 7 of the manual .
3.2 OVERALL BLOCK DIAGRAM
TheModel 3000 is essentially a voltage
controlledoscillator to which phase-
locked loops and a crystal reference
havebeen added for the highfrequency
resolution
.
Thediscussionwill first dealwith the
basic signal generator then it will de-
scribehow the phase-locked loops pro-
vide the additional
accuracy .
3.2
.1
Basic Signal Generator
This discussionbriefly describes how the
RF
is generated and how its frequency
is controlled, also how the signal is
amplified, leveledand amplitude modu-
lated .
Refer to Figure 3-1' for a block
diagram
of the basic signal
generator without
phase locking .
RF
GENERATION
The
RF
output frequency is generatedby
twoUHF oscillators and a mixer .
The
outputs of the two oscillatorsare het
erodyned in the mixer .
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Thedifference
SECTION 3
THEORY OF
OPERATION
frequency is amplified and fed to the
output amplifier .
The frequencies of these oscillators
are controlled byDC voltages applied to
their varactor diodes . The Narrow
Oscillator
yields a single frequency .
The WideOscillator can be programmed
over a range from the frequency of the
Narrow Oscillator to 520 MHz above the
Narrow frequency .
RF FREQUENCY CONTROL
The
RF output
frequency is determined
by programming the frequency of the
Wide
Oscillator
.
TheWide Oscilla-
tor is ultimately
controlled by the
front panelFREQUENCY switches .

The
BCDoutput of these switches is con-
verted to
an analog voltage whichpro-
grams the oscillator in 1 MHz steps .
This analog signal can provideapproxi-
mately
3 MHz accuracy .
RF
AMPLIFICATION AND LEVELING
The RF
power is amplified by a multi-
stage, wide-band amplifier . The flat
output is maintained by a closed-loop
leveling system around this Output Amp-
lifier .
The Leveler includes a Monitor Diode, an
Error Amplifierand a VoltageVariable
Attenuator . The Monitor
detects the
peak of the output of the Output
Amp .
This detected level is compared
to
a
DC
reference by the Error
Amp .
The output
of the
Error Amp
is fed to a PIN diode
(voltage variable)
attenuator,

which
changes the inputlevel to the Output
Amp
until the monitored signal produces
a DC level
equal to the reference level .