HP 203A - Page 15

Model 203A
that
the
FREQUENCY
dialisat
60
and
the
VFO
signal
is
495
kc)
is
applied
tothe
other
input
of
the
balanced
modulator.
Both
signals
are
mixed,
and
the
sum
and
difference
of
these
two
frequencies
will
appear
at
the
output.
The
signal
from
the
balanced
modulator
is
passed
through
an
LC
filter
network
which
is
tuned
for
a
band-pass
offrom
5.4
Mc
to
5.6
Мс,
which
only
allows
the
sum
frequencyto
pass
оп
(о
ће
10:1
divider
A11Q3.
The
10:1
divider
is
similar
to
the
9:1
divider
described
in
paragraph
4-9;
the
maindifference
being
that
the
tuned
tank
circuit
in
the
10:1
divider
is
adi-
usted
so
that
the
stage
provides
an
exact
10:1
division
of
the
input
frequency.
The
resultant
frequency
is
fed
to
the
100
position
of
the
FREQUENCY
MULTIPLIER
switch
and
to
the
mixer
in
the
second
decade
module
А12.
|
4-31.
DECADE
MODULES,
A12
THROUGH
A16.
—_—_—ы——_——
ее
АО.
4-32.
The
action
within
the
succeeding
decade
mod-
ules
is
the
same
as
that
described
for
the
first
decade
module
Ali.
The
output
of
each
module
is
applied
to
а
position
of
the
FREQUENCY
MULTIPLIER
switch
and
to
the
mixer
in
the
following
decade
module.
Thus
a
set
of
variable
frequency
signals
are
produced
and
when
mixed
withthe
constant
high-frequency
signal
in
the
modulator
(A3)
a
beat
frequency
is
produced.
The
.
beat
frequency
is
decreased
bya
factor
of
10
for
each
lower
range
of
the
FREQUENCY
MULTIPLIER
Switch.
4-33.
MODULATOR
ASSEMBLY,
АЗ.
4-34.
The
Modulator
assembly
A3
consists
of
a
mod-
ulator
drive
amplifier
andtwo
balanced
Switching
type
modulators;
one
for
the
REFERENCE
PHASE
channel,
andthe
other
for
the
VARIABLE
PHASE
channel.
Refer
to
the
Schematic
diagram,
figure
5-16,
for
details.
4-35.
MODULATOR
DRIVER
AMPLIFIER.
A————M
MM
ПАРИ
МАРЫІ.
4-36.
The
frequency
selected
by
the
FREQUENCY
dial
and
the
FREQUENCY
MULTIPLIER
is
applied
to
the
input
of
the
modulator
driver
amplifier
A3Q1
where
it
is
amplified
and
applied
to
A3Q2
and
A3Q3.
A3Q2
and
A3Q3
actas
anoverdrivenamplifier
which
ampli-
fies
and
clips
the
signal
applied
to
the
base
ої
A3Q2.
This
operation
produces
a
Square
wave
output
at
the
collector
of
A3Q3
which
is
applied
to
the
modulator
section
as
a
switching
signal.
|
4-37.
REFERENCE
PHASE
CHANNEL
MODULATOR.
4-38.
The
modulator
driving
signal
(У
РО)
anddecade
output)
is
applied
to
the
bases
of
the
switching
trans-
istors
(A3Q5
thru
A3Q8).
The
fixed
frequency,
a
555
Кс
sine
wave,
is
applied
through
series
resistors
to
the
emitters
of
the
switching
transistors.
The
output
at
the
collectors
is
sine
wave
of
the
sum
and
difference
frequencies.
This
signal
is
applied
to
the
low
pass
filter
assembly
A4
(figure
5-18).
The
filter
passes
only
the
difference
frequency,
the
output
is
a
sine
wave
having
a
frequency
that
is
between
0.
005
Cps
and
60
kc
depending
on
the
position
of
the
FREQUENCY
MULTIPLIER
switch
andthe
FREQUENCY
dial
setting
01760-2
Section IV
Paragraphs 4-31 to 4-51
(refer
to
paragraph
1-5
for
Options),
The
output
signal
is
applied
to
the
de
amplifier
A6.
4-39.
А
dc
reference
voltage
is
derived
by
summing
the
signals
at
the
collectors
of
A3Q5
and
A3Q6.
This
dc
reference
voltage
is
used
as
a
reference
voltage
for
the
differential
amplifier
in
the
dc
amplifier
as-
Sembly
Аб.
4-40.
VARIABLE
PHASE
CHANNEL
MODULATOR,
——
4-41.
The
variable
phase
channel
modulator
operates
the
same
as
the
reference
phase
channel
described
in
paragraph
4-37,
except
that
the
output
is
applied
to
the
Low
Pass
Filter
A5
and
then
to
the
dc
amplifier
АЗ.
4-42.
DC
AMPLIFIER
ASSEMBLIES
Аб
AND
A7.
4-43.
After
passing
through
the
low
pass
filter
the
Signal
is
fed
to
the
direct
coupled
amplifiers;
A6
for
the
reference
phase
channel,
and
A7
for
the
variable
phase
channel.
Refer
to
the
schematic
diagrams
Пре
ures
5-18
and
5-20
for
circuit
details.
4-44,
REFERENCE
PHASE
CHANNEL
DC
AMPLIFIER
ASSEMBLY,
4-45.
The
dc
amplifier
usesa
differentia]
amplifier
for
the
input
stage.
The
dc
reference
voltage
from
the
modulator
section
is
used
as
the
reference
input
for
the
differential
amplifier.
This
configuration
minimizes
any
tendency
of
dc
drift
due
to
power
Supply
temperature
variations.
The
de
amplifier
circuit
uses
negative
feedback
to
provide
for
low
dis-
tortion
amplification.
The
output
is
applied
to
a
bridged-T
type
attenuator
and
the
square
wave
gene-
rator
АВ.
4-46.
VARIABLE
PHASE
CHANNEL
DC
AMPLIFIER
ASSEMBLY.
4-47.
The
variable
phase
channel
de
amplifier
oper-
ates
the
same
as
the
reference
phase
channel
des-
сгіреа
in
paragraph
4-44,
except
that
the
output
is
applied
to
bridged-T
type
attenuator
and
the
square
wave
generator,
А9,
.
4-48.
SQUARE
WAVE
AMPLIFIER
ASSEMBLIES A8 AND A9.
4-49,
The
output
sine
wave
from
the
dc
amplifier
is
applied
to
a
square
wave
generator
Section,
А8,
for
the
REFERENCE
PHASE
channel,
and
A9
for
the
VARIABLE
PHASE
channel.
Refer
to
the
schematic
diagrams,
figures
5-18
and
5-20,
for
circuit
details.
4-50,
REFERENCE
PHASE
CHANNEL
SQUARE
WAVE
GENERATOR,
4-51.
The
sine
wave
from
the
de
amplifier
is
ampli-
fied
by
A8Q1
then
applied
to
the
base
of
А892,
АВО?
and
A8Q3
act
as
anover
drivenamplifier
whichampli-
4-3