Eddystone 990R - Page 32

The
pre-set
trimmer
C38
(accessible
through
trimming aperture
in underside cover
of
RP Unit) is
adjusted
during
initial
factory
alignment
to provide
correct
, feedback
phase
for
the
transistor
fitted
at
TR3.
It
is
most
unlikely
that further
adjustment
of
this
trimmer
would
be
required
except
in
the
event of
TR3
being
changed.
An
indication
that
C38
requires
adjustment
is
that
the
oscillator
will cease
to
function
at certain
parts
of
the total
coverage.
In
general,
re-adjustment
to produce
sustained
oscillation
on
one range
will
result
in
correct
performance
on
all four ranges.
Nevertheless,
check
for
correct
operation
at
all
frequencies
before
proceeding
with
alignment of
the
osc-
illator
circuits.
On
completion
of
the
oscillator
alignment,
re-check
the
overall accuracy
on
all
ranges
before
proceeding
with
re-alignment
of
the signal
frequency
circuits.
The
normal
top
cover
should
be
replaced
to
permit
use of
the
internal
calibrator
for
this
test.
RP
Alignment
.
(2.
Signal-frequency
circuits)
Test
Equipment
As
for
alignment
of
the
Local
Oscillator.
As
with
alignment
of
the
oscillator,
alignment
of
the
signal
frequency
circuits
must
commence
at
Range
1.
The
other
ranges
can be
re-aligned
in
any
order.
The
generator
must
be
accurately
matched
to
75fi
and
is
connected
directly
to
the
aerial
input
socket
using a
750
BNC
connector.
The
output meter
should
be
fed from
the
30
terminals
as
before.
Alignment
frequencies
and
adjustments
are
listed in
the
Tables
which
follow,
trimming
following
normal
procedures
with no
requirement
for
special
techniques.
Adjustments
should
be
repeated
as
necessary.
Control
settings
used
in
previous
phases
of
alignment
should
be
retained
with
the
RP/lP
GAINS at maximum
and
the
IP
INPUT
STITCH
in
the
normal
"up"
position.
Bandpass
Range
i
Freq«
Aerial
Primary
Secondary
—
i
240
MHz
C6
C14
C24
2
127
MHz
C2
C15
C20
3
75
MHz
C3
ci6
C21
4
45
MHz
C4
C17
C22
1
130
MHz
LI
L5
L9
2
75
MHz
L2
L6
L10
5
45
MHz
L3
L7
Lll
4
27
MHz
L4
L8
L12
1
On
completion
of
signal
frequency
alignment,
tune
the
receiver carefully
to a
27
MHz
signal
from
the
generator
and
then
adjust
C30
(accessible
below
RP
Unit) . This
trimmer
aligns
the
first
10.7
MHz
(IP)
circuit
and
cannot
be
conveniently
aligned during
normal
IP
alignment
due
to
difficulty
of
access
to a
suitable
generator
input
connection.
Alignment
of
C30
on
the
27
MHz
signal
after
conversion
to
10.7
MHz
in
TR2
is
quite
satisfactory.
Overall
sensitivity
and
noise
factor
should
now
be checked
at several
points
on
each
of
the
four
ranges.
Noise
factor
should
be
better than
lOdB
and
sensitivity
better
than
5
m.V
for
lGdB s/n
ratio
(AM
mode,
NARROW
selectivity,
30fo
modulation
at 400
Hz
and
standard
50mW
output
at 30
outlet).
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