Mars RC-288A User manual
SINGLE
-SIDEBAND
RECEIVER
CONVERTER
Model
RC-288A
135
Eileen
Way,
Syosset,
LI.
SINGLE
-SIDEBAND
RECEIVER
CONVERTER
Model
RC-288A
INSTRUCTION
MANUAL
February
1963
MARS
ELECTRONICS
135
Eileen
Way
Syosset,
L.I.,
N.Y.
:
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TATE
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RSA
NI
SET
Aa
WARRANTY
MARS
ELECTRONICS,
warrants
each
instrument
of
its
manufacture
to
be
free
from
defects
in
material
and
workmanship.
Our
obligation
under
this
Warranty
is
limited
to
servicing
or
adjusting
any
instrument
returned
to
our
factory
for
that
purpose,
and
to
making
good
at
our
factory
any
part
or
parts
thereof
except
tubes,
fuses
or
batteries
which
shall,
within
one
year
after
making
delivery
to
the
original
purchaser,
be
returned
to
us
with
transportation
charges,
prepaid,
and
which
on
our
examination
shall
dis-
close
to
our
satisfaction
to
have
been
thus
defective.
If
the
fault
has
been
caused
by
misuse
or
abnormal
conditions
of
operation,
repairs
will
be
billed
at
cost,
plus
a
small
service
charge.
In
this
case
an
estimate
will
be
submitted
before
the
work
is
started.
If
any
fault
develops,
the
following
steps
should
be
taken:
1.
Notify
us,
giving
full
details
of
the
difficulty,
and
include
the
model
number,
type
number
and
serial
number,
On
receipt
of
this
information,
we
will
give
you
service
instructions
or
shipping
data.
2.
On
receipt
of
shipping
instructions,
forward
the
instrument
prepaid,
and
repairs
will
be
made
at
the
factory.
If
requested,
an
estimate
of
the
charges
will
be
made
before
the
work
begins
provided
the
instrument
or
the
repairs
required
are
not
covered
by
the
warranty.
MARS
ELECTRONICS,
reserves
the
right
to
make
changes
in
design
at
any
time
without
incurring
any
obligation
to
install
same
on
units
previously
purchased.
This
Warranty
is
expressly
in
lieu
of
all
other
obligations
or
liabilities
on
the
part
of
MARS
ELECTRONICS
and
MARS
ELECTRONICS
neither
assumes
nor
authorizes
any
other
person
to
assume
for
them
any
other
liability
in
connection
with
the
sales
of
MARS
ELECTRONICS
instruments.
This
Warranty
applies
regardless
of
conditions
to
the
contrary
that
are
included
as
a
part
of
the
buyer's
purchase
order,
INDEX
Section
I
-
GENERAL
DESCRIPTION
be
General
2;
Specifications
Section
II
-
FUNCTIONAL
DESCRIPTION
1.
General
2.
Circuit
Description
Section
III
-
INSTALLATION
is
Unpacking
Installation
Instructions
tN
Section
IV
-
OPERATION
AND
ALIGNMENT
ier
Controls
and
Indicators
2.
Operating
Instructions
Bi.
Alignment
and
Adjustment
Procedures
Section
V
-
MAINTENANCE
Li
Tube
Socket
Voltages
and
Terminal
Resistance
Section
VI
-
PARTS
CATALOG
5
General
:
Z.
Parts
List
_—
APPENDIX
I
-
Modification
to
RC-288
Receiver
Converter
for
Operation
from
230
volts
Power
Source.
APPENDIX
II
-
Communications
Receiver
AGC
Modifications
General
AGC
Modification
Collins
Receiver,
Type
51
J-1
through
4
Hammarlund
Receiver,
Model
SP-600-JX
RCA
Receiver,
Model
AR-8516
awe
ii
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:
4
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4
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3
Ka
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3
-
2
=
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——
aisle
.
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2
F
Figure
1.
2.
Table
ILLUSTRATIONS
Single
Sideband
Receiver
Converter,
Model
RC-288
Receiver
Converter
RC-288,
Block
Diagram
Receiver
Converter
RC-288,
Schematic
Diagram
Receiver
Converter
RC-288,
Power
Supply
Schematic
Diagram
Power
Supply
Modification
for
230
Volts
50/60
cps
Power
Source
Operation
Modifications,
Collins
Receiver,
Model
51-J
AGC
Modifications,
Hammarlund
Receiver,
Model
SP-600-JX
IF
Modifications,
Hammarlund
Receiver,
Model
SP-600-JX
TABLES
Title
Function
of
Controls
and
Indicators
Voltage
and
Resistance
Measurements
Manufacturers'
Symbols
iil
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SINGLE
SIDEBAND
COMMUNICATIONS
RECEIVER
CONVERTER
Model
RC-288
Section
I]
GENERAL
DESCRIPTION
l.
General
This
section
provides
a
brief
discussion
of
the
virtues
of
single
sideband
communications
including
a
general
description
of
Receiver
Converter,
Model
RC-288,
its
application
and
its
use
in
the
single
sideband
communications
field.
Also
included
in
this
section
is
a
summary
of
the
functional
characteristics
and
features
of
the
single
sideband
Receiver
Converter,
figure
l.
a.
Introduction.
The
techniques
of
single
sideband
and
exalted-
carrier
reception
provide
important
new
tools
to
help
overcome
the
many
difficulties
encountered
in
short
wave
transmission.
By
exalted-
carrier
detection,
the
harmonic
distortion
and
cross
modulation
resulting
from
carrier
fading,
is
removed.
Also,
additional
degrees
of
selectivity
are
provided
that
are
not
available
with
ordinary
diode
detection.
The
use
of
single
sideband
reception
is
a
valuable
aid
in
the
elimination
of
the
very
frequent
interference
which
is
encountered
in
H-F
transmission.
The
long-ranges
from
which
signals
may
be
received
bring
about
so
many
possible
cases
of
interference
that
all
such
devices
become
a
necessity
to
obtain
the
utmost
out
of
an
H-F
communications
system.
When
the
communications
link
is
by
a
single
sideband
transmitter
and
a
single
sideband
receiver,
not
only
is
the
ultimate
realized
with
respect
to
spectrum
economy,
but
a
power
gain
of
9
db
is
realized
with
respect
to
double
sideband
AM
systems.
The
Single
sideband
receiver
converter
unit
is
the
result
of
a
long
period
of
research
devoted
to
the
simplification
of
single
sideband
receiving
equipment.
It
provides
performance
better
than
that
which
is
actually
necessary
for
reception
of
single
sideband
transmissions
of
all
types,
together
with
the
capability
of
reception
of
double
sideband
amplitude
and
phase
modulation
by
exalted-carrier
detection
of
a
single
sideband
only.
The
RC-288
Receiver
Converter
is
capable
of
operation
with
any
communications
receiver
in
which
thel-F
frequency
lies
in
the
range
of
440
kc
to
510
kc.
The
I-F
bandwidth
between
the
minus
1
db
points
of
the
communications
receiver
should
not
be
less
than
12
kc.
The
converter
unit
separates
the
sidebands
of
the
incoming
signal
and
converts
this
sideband
intelligence
into
audio
signals
for
operation
of
terminal
equipment.
These
audio
signals
may
also
be
used
for
redistribution
to
other
landlines
or
communications
circuitry.
The
single
sideband
filters
within
the
receiver
converter
provide
a
reception
of
audio
frequencies
between
250
cps
and
6000
cps.
However,
the
I-F
bandwidth
of
the
communications
receiver
may
be
altéred,
or
3500
cps
filters
may
be
used
in
the
Receiver
Converter
to
lower
the
audio
frequency
response
if
desired.
o,
Types
of
Reception.
The
RC-288
single
sideband
Receiver
Converter
is
intended
for
use
in
applications
between
fixed
installations
having
a
heavy
flow
of
message
traffic.
The
output
signal
of
the
Receiver
Converter
will
be
identical
with
the
multiplexed
signals
delivered
over
the
wires
in
voice-frequency
landline
carrier
telephonic
transmission.
Thus,
the
converter
unit,
operating
in
conjunction
with
a
communications
receiver,
may
be
used
to
feed
carrier
terminal
equipment
that
operates
several
channels
of
teletypewriters,
facsimile,
or
voice
reproducing
equipment.
i
The
single
sideband
Receiver
Converter
is
also
capable
of
the
following
types
of
reception:
(1)
EXALTED-CARRIER
UPPER-SIDEBAND
RECEPTION.
This
type
of
reception
provides
the
optimum
reception
of
double
sideband
signals
for the
case
of
interference
on
the
lower
sideband.
(2)
EXALTED-CARRIER
LOWER-SIDEBAND
RECEPTION.
This
type
of
reception
provides
optimum
performance
for
the
case
of
interference
on
the
upper
sideband.
(3)
SIMULTANEOUS
RECEPTION
OF
THE
UPPER
AND
LOWER
SIDEBAND
CHANNELS
TRANSMITTED
IN
A
SINGLE
SIDEBAND
TWIN-CHANNEL
MULTIPLEX
SYSTEM.
Separate
outputs
are
provided
for
each
sideband
on
the
converter.
Thus,
simultaneous
reception
of
the
separate
programs
on
both
sidebands
may
be
obtained.
For
instance,
a
voice
or
program
channel
might
be
transmitted
on
the
lower
sideband
and
a
multiplex
tone
teletypewriter
system
on
the
upper
sideband.
(4)
REDUCED-CARRIER
OPERATION
WITH
CARRIER
REDUCTIONS
FROM
ZERO
TO
TWENTY
DB
ON
ANY
OF
THE
ABOVE
FORMS
OF
RECEPTION,
The
present
standards
of
commercial
single
sideband
transmission
employ
carrier
reductions
of
ten
and
twenty
db,
depending
upon
the
types
of
programs
being
applied
to
the
transmitters.
The
degree
of
received
carrier
reduction
is
controllable
by
means
of
a
-
CARRIER
COMPENSATION
control
on
the
single
sideband
Receiver
Converter,
Zero
db
carrier
reduction
corresponds
to
ordinary
double
sideband
A-M
transmission.
“C.
Functional
Characteristics.
The
following
paragraphs
describe
the
functional
characteristics
of
the
RC-288
single
sideband
communications
Receiver
Converter:
(1)
AUTOMATIC
FREQUENCY
CONTROL.
Automatic
frequency
control
is
provided
to
maintain
the
signal
carrier
exactly
in
tune
with
the
local
crystal
oscillator.
The
maximum
residual
AFC
error
is
less
than
2cps,
The-system
holds-in
over
a
range
of
+
2000
cps
with
a
pull-in
range
of
50
cps
from
the
center
frequency
of
the
carrier
filter.
The
mechanical
servo
system
is
capable
of
following
an
overall
system
frequency
drift
of
up
to
10
cps
per
second.
a
The
automatic
frequency
control
is
operated
from
the
output
of
the
carrier
filter,
This
"protects"
the
system
from
jamming
signals
since
the
jamming
signals
must
be
exactly
in
the
range
of
the
carrier
filter
to
be
effective.
The
same
"protection"
also
eliminates
the
"sideband
grabbing"
of
the
AFC
system
when
tone
modulation
is
being
received.
(2)
AFC
SQUELCH.
An
automatic
squelch
circuit
stabilizes
the
servo
AFC
circuit
when
there
is
a
decrease
in
the
carrier
signal
below
a
pre-adjusted
operating
level.
Operation
of
the
AFC
squelch
is
indicated
by
a
visual
alarm.
(3)
LOCAL
CARRIER
OSCILLATOR,
A
local
carrier
oscillator,
tuned
to
the
incoming
carrier
by
the
use
of
a
crystal
oscillator
which
is
tuned
to
the
mid-frequency
of
the
crystal
carrier
filter,
is
provided
for
single
sideband
reception.
Operation
with
the
local
carrier
oscillator
provides
complete
protection
against
carrier
fading
effects
and
also
serves
as
an
aid
in
tuning
weak
signals
and
in
tuning
complex
multiplex
single
sideband
signals,
(4)
RECONDITIONED
CARRIER.
The
filtered
and
limited
"recon-
ditioned
carrier''
may
be
used
as
well
as
the
local
carrier
oscillator.
The
reconditioned
carrier
is
used
for
all
double
sideband
reception
or
may
be
used
with
single
sideband
reception
if
it
is
desired
to
receive
modulation
material
which
is
sensitive
to
the
frequency
error
between
the
incoming
carrier
and
the
local
carrier.
(5)
DRIFT
CORRECTION
INDICATOR.
A
direct
reading
drift
correction
indicator
is
provided
to
indicate
the
amount
of
detuning,
in
the
receiver.
The
scale
is
calibrated
in
increments
of
500
cps
between
minus
2000
cps
and
plus
2000
cps.
(6)
CARRIER
STRENGTH
METER,
This
meter
indicates
the
incoming
signal
level
and
provides
an
indication
for
determining
when
the
signal
is
properly
tuned.
(7)
AUDIO
OUTPUT
METER.
This
meter
indicates
the
audio
output
level
in
VU
units.
Switching
is
provided
for
monitoring
either
the
upper
or
lower
sideband.
Two
ranges,
0
VU
and
+10
VU,
are
provided
as
well
as
an
OFF
position,
which
may
be
utilized
while
retuning
to
another
frequency.
HRBEBREBEERRRER
SESE
EE
EZ
hin
(8)
AGC
SYSTEM.
The
automatic
gain
control
may
be
controlled
by
a
signal
with
a
fast-attack/slow-decay
time
constant
on
either
sideband
for
the
reception
of
suppressed
carrier
single
sideband
voice
or
program
modulation.
The
AGC
system
may
also
be
regulated
by
the
usual
carrier-controlled
AGC
method
or
the
total
signal
(DSB)
AGC
signal.
Control
by
the
total
rectified
signal
is
advantageous
for
tuning
purposes.
Control
by
the
rectified
filtered
carrier
or
side-
bands
is
advantageous
for
rejecting
interference
and
jamming
which
might
obtain
control
of
the
AGC
system.
Zs
Specifications
All
specifications
for
the
single
sideband
Receiver
Converter
Model
RC-288
are
divided
into
two
categories;
electrical
and
physical.
a.
Electrical.
The
electrical
specifications
of
this
unit
include
all
electronic
characteristics
as
well
as
the
primary
power
require-
ments,
These
specifications
are
listed
as
follows:
(1)
PRIMARY
POWER
REQUIREMENTS
115/230
volts
#10
percent
50/60
cps
single
phase,
200
watts.
(2)
AUDIO
OUTPUT
410
dbm
at
600
ohms,
each
channel,
balanced.
(3)
AUDIO
FREQUENCY
RESPONSE
Within
+
2
db
from
250
cps
to
6000
cps.
ag
(4)
TOTAL
HARMONIC
AND
CROSS-MODULATION
DISTORTION
Overall
distortion
is
less
than
2
percent
at
rated
power
output.
(5)
HUM
AND
NOISE
LEVEL
-60
db
or
better.
(6)
METERING
FACILITIES
a.
Carrier
meter
is
operated
by
diode
rectifier
in
carrier
channel
of
the
single
sideband
adapter.
.
i
b.
Drift
correction
indicator,
mechanically
connected
to
AFC
servo
system,
displays
tuning
drift
to
maxi-
mum
of
+
2000
cps.
q
i
c.
Audio
output
meter
monitors
either
upper
or
lower
sideband
output.
Range
0
VU
or
+10
VU.
(7)
MONITOR
OUTPUT
The
monitor
amplifier
may
be
switched
to
either
upper
or
lower
sideband
audio
output.
(8)
TERMINAL
CONNECTIONS
a.
Terminal
for
each
audio
output
channel.
b.
AGC
Terminal.
c.
UG
-
625/U
I-F
INPUT.
b,
Physical.
The
physical
specifications
of
the
RC-288
Receiver
Converter
are
provided
in
the
following
list:
WEIGHT
58
pounds
MATERIAL
Chassis
and
Front
Panels
-
Aluminum
FINISH
Medium
Grey,
Semi-Gloss
White
Lettering
MOUNTING
OF
EQUIPMENT
Chassis
is
in
horizontal
position;
all
tubes
vertical.
DIMENSIONS
Width,
19
inches
Height,
8
3/4
inches
Depth,
17
1/2
inches
Section
IT
FUNCTIONAL
DESCRIPTION
Le
General
The
following
paragraphs
provide
a
functional
description
of
the
RC-288
single
sideband
communications
Receiver
Converter.
Referring
to
the
block
diagram,
figure
2,
and
the
schematic
diagrams,
figures
3
and
4,
an
illustrative
signal
will
be
traced
through
the
con-
verter
and
the
functions
of
the
circuits
described.
os
Circuit
Description
The
intermediate
frequency
from
the
communications
receiver
is
fed
into
the
RC-288
Receiver
Converter
through
a
tuned
I-F
transformer
to
Mixer
VI.
The
signal
from
the
variable
R-F
.
oscillator,
V25,
is
applied
to
the
grid
of
VI
where
it
is
heterodyned
with
the
receiver
IF
producing
a
new
intermediate
frequency
of
100
kc.
The
100
kc
intermediate
frequency
is
amplified
in
I-F
Amplifier
V2
and
applied
to
Sideband
Cathode
Followers
V3-A
and
V3-B
and
Carrier
Amplifier
V9.
Sideband
Cathode
Follower
V3-A
applies
the
signal
to
the
deflecting
electrodes
of
Product
Detector
V4
through
an
upper
sideband
crystal
filter,
FL-l1.
This
filter
has
a
pass
band
from
100
kc
to
106
kc.
Likewise,
Cathode
Follower
V3-B
applies
the
signal
to
Product
Detector
V6
through
a
lower
sideband
crystal
filter,
FL-3,
which
has
a
pass
band
from
94
kc
to
100
kc.
Incorporated
with
Carrier
Amplifier
V9
is
the
variable
CARRIER
COMPENSATION
control
which
compensates
for
the
sup-
pressed
carrier
level
from
0
to
20
db.
The
amplified
carrier
output
of
V9
is
fed
to
a
100
kc
crystal
carrier
filter,
FL-5,
which
has
a
pass
band
of
50
cps,
rejecting
all
sideband
frequencies.
The
filtered
carrier
is
then
applied
to
the
AGC
SELECTOR
and
carrier
amplifier
V10-A.
The
output
from
this
carrier
amplifier
is
fed
to
Squelch
Driver
V10-B
and
to
Limiter
V12.
The
output
from
the
two
stages
of
limiting
is
applied
to
Frequency
Multiplier
V13
and
also
to
one
side
of
the
local
carrier-reconditioned
carrier
(LC-RC)
CARRIER
INSERTION
switch.
Connected
to
the
other
side
of
the
CARRIER
INSERTION
switch
is
the
crystal-controlled
100
kc
local
oscillator,
V15.
The
output
from
Local
Oscillator
V15
is
also
fed
to
a
second
frequency
multiplier,
V14,
which
is
compared
against
the
output
of
frequency
multiplier
V13
in
a
phase
error
detector
network.
This
action
will
be
discussed
in
later
paragraphs.
The
output
of
the
CARRIER
INSERTION
switch
is
connected
to
the
control
grid
of
Product
Detectors
V4
and
V6.
With
the
appli-
cation
of
the
incoming
local
or
reconditioned
carrier,
the
product
detectors
demodulate
the
applied
intermediate
frequency.
The
output
of
each
product
detector
is
next
passed
through
its
respective
6
kc
low
pass
filter,
FL-2
or
FL-4,
to
the
SIDEBAND
SELECTOR
and
the
AGC
SELECTOR.
The
function
of
the
SIDEBAND
SELECTOR
is
to
provide
a
convenient
method
of
switching
the
upper
sideband
and
lower
sideband
between
LINE
A
and
LINE
B.
Each
output
from
the
SIDE-
BAND
SELECTOR
is
applied
to
an
associated
audio
amplifier.
The
audio
amplifier
provides
the
audio
signal
for
the
balanced
600
ohms
output
terminals
on
the
back
panel
and
the
paralleled
MONITOR
SELECTOR.
The
MONITOR
SELECTOR
switch
applies
either
line
signal
to
the
monitor
amplifier,
V8,
which
feeds
the
audio
signal
to
the
600
ohms
phone
jack
on
the
front
panel.
The
output
from
the
MONITOR
SELECTOR
is
also
applied
to
a
VU
meter
circuit
which
provides
visual
aid
for
monitoring
and
setting
the
level
of
each
line.
The
AGC
voltage
can
be
obtained
from
the
carrier
(CAR),
upper
sideband
(USB),
lower
sideband
(LSB),
or
the
total
signal
(DSB)
with
the
AGC
SELECTOR.
The
desired
AGC
voltage
is
amplified
by
AGC
Amplifier
V24
and
detected
by
AGC
Diode
V23.
The
I-F
gain
is
obtained
by
applying
a
positive
''bucking'"
bias
to
the
AGC
voltage.
In
the
USB
and
LSB
position
of
the
AGC
SELECTOR,
a
fast-attack/
+
slow-decay
AGC
is
obtained.
Qo
The
AFC
circuit
consists
of
the
two
frequency
multipliers,
a
phase
error
detector
network,
the
AFC
motor
and
drive
amplifiers
and
the
AFC
squelch
circuit.
The
total
output
torque
of
the
AFC
motor
is
a
function
of
the
frequency
of
field
expansion/decay
due
to
winding
current.
Because
of
this
fact,
the
fundamental
of
the
100
kc
carrier
and
local
carrier
signals
are
fed
into
frequency
multipliers
which
select
and
amplify
the
third
harmonic
as
the
operating
frequency.
Thus,
the
effective
error
frequency
is
triple
the
actual
error,
thereby
tripling
the
motor
sensitivity.
The
output
of
each
frequency
multiplier
is
then
fed
into
a
phase
error
detecting
network.
;
:
g
J
]
j
af
The
output
signals
of
Frequency
Multipliers
V13
and
V14,
which
appear
across
the
secondary
of
transformer
T6,
produce
voltage
drops
across
the
elements
of
a
phase
shifting
network.
Since
the
effective
operating
frequency
lies
within
a
narrow
band
about
300
kc
+
6
kc,
the
capacitance
and
resistance
values
have
been
chosen
to
produce
an
equal
reactive
voltage
drop
in
across
R116,
C60,
C6l
and
R117..
Although
the
reactive
voltage
drop
in
each
leg
is
equal,
the.
signals
appearing
across
each
of
the
capacitive
legs
produce
a
phase
shift
of
90
degrees
with
respect
to
each
other.
This
signal,
with
the
necessary
phase
relationship,
is
then
used
to
drive
the
phase
rectifiers.
The
instantaneous
phase
displacement
of
the
two
300
kc
signals
(assuming
there
is
some
error
in
the
carrier
frequency
relative
to
the
frequency
of
Crystal
Oscillator
V15)
is
translated
in
each
rectifier
into
an
output
voltage,
This
voltage
will
be
varying
in
amplitude
and
polarity
at
the
difference
frequency
existing
between
the
two
input
signals.
\While
the
rms
value
of
the
output
rectifiers
is
virtually
equal,
the
instantaneous
output
across
the
load
of
one
differs
from
that
of
the
other
by
the
90
degree
phase
shift.
A
frequency
error
in
which
the
carrier
frequency
is
higher
than
the
crystal
oscillator
will
result
in
the
output
voltage
of
one
rectifier
leading
that
of
the
other
by
90
degrees.
Similarly,
a
frequency
error
in
which
the
carrier
frequency
is
lower
than
the
crystal
oscillator
will
result
in
the
output
voltage
of
the
corresponding
rectifier
to
be
lagging
that
of
the
other
by
90
degrees.
The
voltage
produced
by
each
phase
rectifier
excites
the
associated
grid
of
Amplifier
V16.
The
partially
clipped
sinusoidal
voltage
at
each
plate
of
this
amplifier
drives
a
subsequent
DC
amplifier,
V17
and
V20,
through
the
cut-off/conduct
cycles
thus
generating
a
square
wave
signal.
This
square
wave
excitation
is
fed
to
the
motor
drive
amplifiers,
V19
and
V22,
and
the
inverter
stage
driving
the
ballast
tubes,
V18
and
V21.
Cathode
current
in
one
of
the
parallel-connected
motor
drive
amplifiers
produces
the
field
in
the
second
winding.
The
direction
of
rotation
is
determined
by
the
lead-
lag
relationship
between
the
current
in
one
winding
relative
to
that
in
the
other
winding.
The
motor
drive
output
is
directly
coupled,
through
a
600:1
gear
reduction,
to
the
shaft
of
the
variable
condenser
associated
with
R-F
Oscillator
V25.
When
torque
is
applied
to
this
condenser,
the
R-F
oscillator
will
be
readjusted
to
return
the
frequency
to
within
2
cps
or
less
of
that
necessary
to
produce
the
converted
I-F
center
frequency.
A
front
panel
scale,
calibrated
to
range
limits
between
minus
2000
cps
and
plus
2000
cps,
provides
a
direct
reading
of
the
error
of
the
carrier
a
@
=
frequency.
A
visual
indication
of
the
AFC
motor
action
is
provided
by
an
indicator
disc
coupled
to
the
gear
drive
assembly.
This
aid
becomes
particularly
valuable
to
indicate
drift
and
correction
of
a
—~
relatively
slow
rate
which
would
not
be
perceptible
in
the
motion
of
the
DRIFT
CORRECTION
knob,
When
the
amplitude
of
the
carrier
drops
below
some
pre-
determined
value,
as
set
by
Squelch
Threshold
potentiometer
R90,
Squelch
Amplifier
V11
will
operate
Relay
RY1.
One
set
of
contacts
of
RY1
will
disable
the
AFC
circuit
by
cutting
off
amplifier
V16
(assuming
AFC
switch
S-6
is
in
the
ON
position).
The
second
set
of
contacts
will
illuminate
the
ALARM
indicating
lamp
on
the
front
panel
warning
the
operator
of
the
disabled
condition
of
the
AFC
circuit.
The
output
from
Squelch
Driver
V10-B
is
also
used
as
the
signal
which
is
fed
to
the
carrier
meter
diode.
Rectification
within
diode
CR3
provides
an
appropriate
current
sample
for
the
SET
CARRIER
meter
mounted
on
the
front
panel.
The
SET
CARRIER
meter
indicates,
on
a
linearly
marked
scale
with
a
red
reference
at
mid-scale,
the
level
at
which
to
maintain
the
carrier
during
operation.
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