Theory Of Operation; Introduction; Overall Block Diagram - Wavetek 3000 Instruction Manual

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
The Model 3000 is essentially a voltage
controlled oscillator to which phase-
locked loops and a crystal reference
have been added for the high frequency
resolution .
The discussion will first deal with the
basic signal generator then it will de-
scribe how the phase-locked loops pro-
vide the additional accuracy .
3 .2 .1
Basic Signal Generator
This discussion briefly describes how the
RF is
generated and how its frequency
is controlled, also how the signal is
amplified, leveled and 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 generated by
two UHF oscillators and a mixer .
The
outputs of the two oscillators are het
erodyned in the mixer . The difference
SECTION
3
THEORY OF OPERATION
frequency is amplified and fed to the
output amplifier .
The frequencies of these oscillators
are controlled by DC voltages applied to
their varactor diodes . The Narrow
Oscillator yields
a single frequency .
The Wide Oscillator 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 .
The Wide Oscilla-
tor is ultimately
controlled by the
front panel FREQUENCY switches . The
BCD output of these switches is con-
verted to an
analog voltage which pro-
grams the oscillator in 1 MHz steps .
This analog signal can provide approxi-
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 Amplifier and a Voltage Variable
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 input level to the Output
Amp until the monitored signal produces
a DC level equal to the reference level .