Eddystone 990R - Page 33

Adjustment of
the
AGC Level
Controls
.
The two pre-set
AGC
LEVEL CONTROLS
(RE
AGC
-
RV5
&
IP AGC
-
RV
6
)
are
located
on
the
left-hand side-plate
and should be
set
as
follows
s-
1. Set
the
RF
&
IF GAIN CONTROLS
to
maximum.
2.
Set
the
MNUAL/AGC
SWITCH to
the
"MANUAL"
position.
3
*
Connect multi-range
voltmeter
negative lead to
earth.
4*
Connect multi-range
voltmeter
positive lead
to
centre tag
of
S
6
B.
Note
reading.
5
.
Set
MNUAL/AGC
SWITCH to
"AGC". Adjust
RV6
to obtain
reading
equal to
that
in
( 4)
above.
6
. Transfer
multi-range
meter to
centre
tag
of
S
6
A.
Switch
back
to "MANUAL"
and
note
reading.
7
.
Revert to
"AGC" and adjust
RV5
for
identical
reading.
8. Re-adjust
RV5
slightly
to ensure
that the
control
voltage
is
just
within the
stab-
ilisation range
of
the zener diode
D
6
which
provides
the
RP
AGC
delay.
9
. Check
AGC
characteristic at
190
MHz on
Range
1 and
ensure that performance
is equal
to
or
better than
lOdB change in
output
for
80&B
change in
input
(taken
from
refer-
ence level
of
lOjjiV).
If. performance
is
not to
specification, adjustment
of
the RP AGC
AMPLIFIER GAIN
RY2
will be necessary
though in most cases
alteration
of
the initial
factory
setting
of
this
control
is
most unlikely.
RV2
is
located on
the main
IP
board
and
should be adjusted
by
small
increments,
checking
after
each
adjustment
what
effect
is
produced on the
overall
AGC
performance.
Further adjustment
of
RV
5
may
be
found
necessary
if
major re-adjustment
of
RV2
is
called for.
Low-level
(6000)
Audio
Sensitivity .
With
1000
Hz
signal
applied across
LINE
LEVEL
CONTROL
(set
to
maximum),
an input of
1.75mV should
produce
an
output
of
ImW
in 6000.