Eddystone 990R - Operation; Control Functions; Tuning; System Switch

OPE
RATION
22L
I
??2L!'2?£^2?§
Tuning
*
This
control is
conveniently
located
at
the right-hand
side of
the
receiver
and
operates
the ganged
tuning capacitors
in
the
RF
Tuner Unit
through
a precision
gear
drive
having
a
reduction
ratio
of the order
100s 1.
Logging
scales
are
provided on the
skirt of the
control
knob and
at the
foot
of
the
main
tuning
dial*
Calibration on
the
latter
runs from 0-5000
with
index
marks
at
100-
division intervals.
The
control knob
makes
one complete revolution
per
100-divisions
of
the main scale
and
is
marked
0-100
to permit
interpolation between
the
main
scale
markings.
All
scaling
is arbitrary
and unlike
the
frequency
scales shows
an
increase
in reading
with
movement
of
the
cursor
from
left to
right.
Tuning rate
varies
between
3MHz/rev. and
0*5MHz/rev.
at the
centres
of
Range 1
and
Range
4
respectively.
Range Switch .
The RANGE
SWITCH is
situated
immediately
to
the left of
the 'TUNING CONTROL
and
must
be
pushed
towards
the panel to engage
with
the
gear
drive to the
switch selector
proper.
The panel
control is thus
isolated from
the
remainder
of the
mechanism,
a
simple
precaution
which
virtually
eliminates any possibility
of
random
frequency
change
caused
by
shocks
inadvertently
transmitted
to the
Tuner Unit via
the
switch
mechanism.
.
Range
indication is
'
provided by
a
lamp
display
at
the
left-hand end
of the
scale
plate. Clockwise
rotation
of the
RANGE
SWITCH selects
a'
higher
frequency
range.
System Switch .
Selection
of
the
desired mode of local
oscillator
control
is handled'
by
the SYSTEM
SWITCH. Three modes
of
operation are
possible, vizi-'
1. Manual
tuning
using
the
tunable receiver oscillator
("normal”
mode
marked
"N").
2.
Fixed
freq.
working using
the crystal
controlled receiver
oscillator
(posns
1-8)
.
3*
Operation with
external oscillator
drive for
high- stability
applications
where
flexibility in
frequency
adjustment
is of
prime importance
(marked
"EXT").
Note
that when
using
modes
(2)
and
(
3
)
above,
it
is necessary
to
adjust
the TUNING
CONTROL
and
RANGE
SWITCH to ensure
that
the
signal frequency
circuits
are
aligned
to
the
correct
channel.
The
built-in
meter
can
be
used
as
an
aid
to
accurate
tuning.
Mode
Switch .
This
control
combines
supply
switching (on
both AC
and
DC
operation)
with
selection
of
the
desired
signal
mode.
The
four
positions
are
marked
s-
"
SUPPLY
OFF"
-
"CW"
-
"AM"
-
"EM"
The supply
is
completed
to
the
receiver
by
moving to the
"CW"
position
and remains
connected
in
the
other
two
positions. Illumination
of
one of
the range
indicator lamps
will
show
that the
supply is
"on".
Mode
selection
is
accomplished
by switching
the
audio
outputs
of the
separate
circuit branches.
The
supply
is
disconnected
from
the
CW
Detector
except
at
"CW".
Meter
switching
is a
further
associated function performed
by the MODE
SWITCH.
The
meter is
arranged
to operate
with
centre-zero for "EM" and
normal
left-hand zero
for
"CW" and
"AM"
reception.
A
pre-set zero adjustment
is provided
for the two
latter
modes.
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