Eddystone 990R - Page 22

4.
Set
SYSTEM
SWITCH
to
"N"
("Normal")
for
operation with
internal
tunable
oscillator.
5.
Select
the
appropriate
range,
remembering
to
press
the
RANGE
SWITCH to
engage
the
selector
mechanism.
Carry
out a
calibration
check by
following
the
procedure
out-
lined
below
i-
(a)
Set
controls
as
follows
s-
MODE
SWITCH
SELECTIVITY
mafual/agc
MUTING
"PM"
.
"NARROW"
.
"MANUAL"
.
"OFF"
.
RF GAIN
IF
GAIN
AF
GAIN
Maximum.
Maximum.
For
convenient output.
(b) Move
CALIBRATOR
SWITCH
to
"ON"
and
tune to
the
calibration
marker at the nearest
crystal
check-point
to
the
required
frequency.
(Check-points
are
available
at
10
MHz
intervals
on
all
ranges
-
i.e.
30
&
40
MHz
on
Range
4?
50,
60
&
70
MHz
on
Range
3
etc.)
(c)
Adjust
TUNING
CONTROL
carefully
for
centre-zero
meter
reading
(see
page
20)
and
then
set
CALIBRATOR
SWITCH
to
"OFF".
(d)
Maintain
present
setting
of
TUNING
CONTROL
and
adjust
CAL
RE-SET
CONTROL to
re-
position
the
cursor
coincident
with
the
check-point
calibration
mark.
(e)
Tune
to
required
frequency.
6.
Select
appropriate
MODE
and
set
bandwidth
to
"WIDE"
or
"NARROW"
as
required.
7.
Set
MANUAL/AGC
SWITCH
to
suit
signal
conditions
and
then
re-adjust
all GAIN CONTROLS
for
required
audio
output
(RF/lF
GAINS
are
inoperative
at
"AGC")
.
8.
Introduce
muting
facility
if
required
(see
below).
Operation
with
Muting.
The
internal
muting
circuits
can
be
used
to
advantage
when
the
receiver forms
part
of a
communications
set-up.
In
this
type of
operation,
the
considerable
reduction in
operator
fatigue
which
results
from
elimination
of
inter-station
noise is
a
worthwhile
feature
of
which
advantage
should
be
taken
whenever
possible.
The
muting
system
is
brought
into
operation
by
putting the panel
MUTING
SWITCH
to
the
"ON"
position
and
is
set
to
suit
prevailing
conditions
by
adjustment
of the
pre-set
MUTING
GAIN
CONTROL
at
the rear
of
the receiver.
The
circuit
is
effectively
a
carrier-controlled
system
in
which the receiver
is
silenced
with
a
relay
which is
operated
by a
DC voltage
derived
from
amplified
noise
present
in
the
absence
of a
signal.
The
MUTING
GAIN
CONTROL
sets the gain
of
the
noise
amplifying
stages
which
can
be
adjusted
to
suit
the
level
of
noise prevailing
on
the
particular
frequency
in use.
Adjustment
should
be carried
out
as
follows
s-
1.
With
the
MUTING
SWITCH at
"OFF"
and
the
MUTING
GAIN
CONTROL fully anti-clockwise
tune
to
the
required
signal
and
adjust
all
controls
for optimum reception.
2.
Off-
tune
slightly
to a
clear
channel
adjacent
to the
signal
frequency in
(l)
and
put
the
MUTING
SWITCH
to
"ON".
3.
Advance
the
MUTING
GAIN
CONTROL
in
a
clockwise
direction, stopping at
the
setting
where
the
receiver
becomes
silenced.
4.
Re-tune
to
the
required
signal
frequency
and
ascertain
that receiver un-mutes
satis-
factorily
in
the
presence
of a
carrier.
5
.
Check
muting
performance
when
station
ceases
transmission.
Receiver should
silence
immediately
with
no
tendency
to hang
before
closing.
Re-adjust
MUTING GAIN
CONTROL
if
necessary.
-
21
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