Eddystone 990R - Muting Switch

Selectivity
Switch ,
Provides
.
"WIDE"
(200
kHz)
or
"NARROW"
(30
kHz
-
standard)
bandwidths
to
suit
recep-
tion mode
and
signal
characteristics.
Switching is
accomplished
"electronically",
the
panel
switch
merely
completing
power supply
circuits
to
the
appropriate
switching
stages.
A
crystal
filter
is
used
for
the
"NARROW"
selectivity
position.
NB
Alternative
filters
can
be
fitted
to
order
in the
"NARROW"
position only.
RP and
IF Gains
.
These
two
controls
are
combined
in
one assembly
comprising
two
wirewound potentio-
meters
with
concentric
spindle
drives. The
smaller
control
knob
(with
red index)
is
the
RP
GAIN.
Both
controls
are
taken
out
of
circuit
and are
totally
inoperative with
the
MANUAL/AGC
SWITCH
at
"AGC"
.
AP
Gain
Control .
Controls
the
level
of
audio
at
the
high-level
outputs
feeding
telephones, internal
speaker
and
external
speaker.
Adjustment of
this control
does
not
significantly
affect
output at
the
low-level
line
termination.
6000
Line
Level .
Prov'icAee
independent
adjustment
of
audio
level
at the
6000 line
output.
The
control
is
preset
and
is
located
at
the rear
of
the
receiver.
Interaction between this
control
and
the
AP
GAIN on
the
high-level
channel is
negligible.
External line-
monitoring
facilities
should
be
provided
to
permit
accurate
adjustment
of
this control.
Maximum
output
is
limited
to
lOmW.
Manual
/AGC
Switch
.
Provides
for
manual
or
automatic
control of
gain in the
RP
and
IP
Stages
of
the
receiver.
The
manual
RP
and
IP controls
are
totally
inoperative,
when the switch is set
to
"AGC”.
AGC
will
be
found
of
greatest
value
during general
search
tuning
or when
monitoring
a
channel
occupied
by
stations
spread
over
a
wide area,
when
considerable
variation
in strength
is
likely.
In
most
other
circumstances,
and especially when
receiving
PM signals,
manual
control
will
usually be
found
quite
satisfactory.
It
should
be
noted
that
the
tuning
meter
remains
operative
in
both
positions of this
switch,
scaling
being
logarithmic
at
"AGC"
and
linear
voltage at
"MANUAL"
.
Muting
Switch
.
Placing
the
MUTING
SWITCH to
"ON"
introduces
a
carrier-controlled muting
circuit
to
suppress
noise
output
in
the
absence
of
a received
signal.
This
facility
is
primarily
intended
for use
when
the
receiver
is
employed
in a
communications role
and leads
to
considerable
reduction
in
operator
fatigue
on
long
listening watches.
All
outputs
are
muted
simultaneously
and
a relay
circuit
is
available for
local or
remote signalling.
(Refer
to
further
information
on
page
21
.
)
Muting
Gain
.
This
is
a
pre-set
control
at
the rear
of
the
receiver
and
provides
a
means
of
ad-
justing
the
muting
threshold
to
suit the
level
of
noise
present
in the
absence
of
a
signal.
The
control
should
be
re-adjusted
whenever
the operating frequency
is
changed.
Circuit
design
is
such
that
consistent
relay
operation
is
maintained
over
a
wide range
of
ambient
temperature.
Refer
to
"TUNING
INSTRUCTIONS"
for
setting-up
procedure.
-
19
-