HP 203A - Principles of Operation; Overall Description; RF Amplifiers (А2)

Model 203 А
Section IV
Paragraphs 4-1 to 4-19
SECTION IV
PRINCIPLES
OF
OPERATION
4-1. OVERALL DESCRIPTION.
4-2.
This
section
describes
how
the
Model
203A
Variable
Phase
Function
Generator
operates.
The
block
diagram,
figure
4-2,
shows
the
main
sections
and
the
signal
flow
within
the
Model
203A.
4-3.
The
Model
203A
is
a
beat-frequency
oscillator
which,
by
mixing
two
high-frequency
signals,
generates
Signals
in
the
frequency
range
of
0.005
cps
to
60
kc
(геїог
to
paragraph
1-5
for
options).
One
of
the
high-
frecaency
signals
is
a
fixed
frequency;
the
other
is
var.ible.
The
Model
203A
has
two
signal
channels,
RE:
ERENCE
PHASE
and
VARIABLE
PHASE,each
of
waich
produces
a
sine-wave
signal
and
a
square-
wave
signal.
The
two
channels
are
electrically
simi-
lar
except
that
the
VARIABLE
PHASE
channel
con-
tains
a
continuously
adjustable
phase-shifting
circuit
which
changes
the
phase
relationship
of
the
VARI-
ABLE
PHASE
OUTPUT
with
respectto
the
REFER-
ENCZ
PHASE
OUTPUT.
The
four
signals
(two
re-
ference
phase
and
two
variable
phase)
are
available
simultaneously
at
the
OUTPUT
connectors.
4-4.
The
fixed
frequency
signal,
which
is
generated
by
a
crystal
oscillator,
is
applied
toboth
channels
and
routedto
a
modulator
through
an
RF
Amplifier
within
each
channel.
The
variable
frequency
signal
is
applied
directly
to
the
modulator
of
each
channel.
The
fre-
quency
of
the
variable
frequency
signal
is
controlled
by
the
position
of
the
FREQUENCY
dialand
the
setting
of
the
FREQUENCY
MULTIPLIER
switch.
Thesetwo
Signals
are
mixedin
the
modulator
and
the
difference
іп
frequency
between
the
two
signals
is
the
output
frequency
of
the
Model
203A.
4-5.
CRYSTAL
OSCILLATOR
AND
DIVIDER
ASSEMBLY
(АТ).
|
4-6.
Assembly
Al
consists
of
а
crystal
controlled
oscillator
and
a
9:1
frequency
divider.
Refer
to
the
Schematic
diagram,
figure
5-10,
for
circuit
details.
4-7.
CRYSTAL
OSCILLATOR,
4-8.
The
oscillator
(А1У1апа
A1Qi)is
a
crystal
con-
trolled
grounded
base
Colpitts
oscillator.
The
5
Mc
output
is
applied
through
buffer
amplifier
A1Q2,
for
isolation,
to
the
base
of
the
9:1
frequency
divider.
4-9.
9:1
FREQUENCY
DIVIDER.
4-10.
The
9:1
divider
consists
of
a
divider
A1Q3
and
а
tank
circuit
which
consists
of
А1С8,
А1С9,
АІСІІ,
and
A1L2,
The
divider
is
basically
a
class
С
grounded
base
Colpitts
oscillator.
Цаг
4-11.
Two
things
occur
duringeach
cycle
of
the
divi-
der
operation,
One
is
amplitude
modulation
of
the
Signal
applied
tothe
base
of
A1Q3,
and
the
second
is
a
mixing
action
within
А103.
Each
function
occurs
at
01760.2
a
different
time
during
each
cycle
of
oscillation
and
together
tend
to
synchronize
A1Q3
with
a
sub-multiple
frequency
of
the
frequency
applied
to
the
base
of
the
divider.
4-12,
Divider
A1Q3
operates
in
the
region
of
voltage
Saturation
for
a
portion
of
each
cycle.
During
the
saturation
period,
the
impedance
betweenthe
base
and
collector
of
A1Q3
becomes
very
low;
for
the
rest
of
cycle
the
impedance
between
the
base
and
collector
is
relatively
high.
The
variation
in
impedance
between
base
and
collector
of
A1Q3
results
in
amplitude
mod-
ulation
(about
10%)
of
the
signal
on
the
base
of
the
divider.
This
amplitude
modulation
creates
sidebands
at
the
8th
and
10th
harmonic
of
the
divider
oscillating
frequency.
4-13.
The
signal
applied
to
the
base
of
A1Q3
is
about
4.
995
Mc
which
is
generated
by
the
crystal
oscillator
circuit.
The
tank
circuit
of
the
9:1
divider
is
tuned
so
that
A1Q3
is
oscillating
at
the
9th
sub-multiple
frequency
of
4.995
Mc
(555
Кс).
4-14.
The
mixing-process
within
A1Q3
occurs
at
the
time
during
each
cycle
when
the
divider
just
starts
to
conduct.
During
this
short
time,
the
8th
and
10th
harmonic
of
the
555
ke
signal
are
mixed
with
the
9th
harmonic
resulting
in
а
frequency
component
at
555
ke
which
influences
the
oscillations
of
A1Q3.
The
result
is
that
А193
stays
synchronized
to
the 9th
sub-har-
monic
of
4,
995
Mc.
4-15.
The
pitype
tank
circuit
filters
out
harmonic
frequencies
which
may
be
present
at
the
collector
of
А193.
A
buffer
amplifier
A1Q4
provides
further
filtering,
isolation,
and
power
gain.
The
output
of
the
9:1
divider
is
a
555
kc
signal
and
is
coupled
by
А1Т2
to
A2Q1
and
A2Q2
(see
figures
5-10
and
5-12).
4-16.
VARIABLE
PHASE
SHIFTER
ASSEMBLY.
4-17.
The
variable
phase
shifter
assembly
A25
(figure
5-12)
is
a
goniometer
consisting
oftwostator
windings,
a
rotor
winding,
and
associated
circuits,
The
goniometer
requires
two
555
kc
input
signals;
one
‚
from
A2Q2
toone
ofthe
stator
windings,
and
the
other
from
A2Q1
and
the
90?
phase
shift
networktothe
other
stator
winding.
The
output
phase
corresponds
to
the
angle
of
the
rotor
winding
(PHASE
LAG
control).
The
phase
can
be
continuously
adjusted
from
0
through
360?
with
respect
to
the
reference
signal
while
maintaining
a
constant
amplitude.
The
adjustable
phase
shifter
output
is
applied
to
the
RF
amplifier
assembly
A2
(figure
5-12).
4-18. RF AMPLIFIERS (A2).
4-19.
The
RF
amplifier
assembly
A2
consists
of
two
RF
amplifiers;
A2Q3,
A2Q4,
and
A2Q5
for
the
reference
phase
channel
and
A2Q6
through
A2Q9
for
4-]