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7-12
MICROPHONE UP/DOWN
OPERATION
•FREQUENCY CONTROL
•MEMORY
CHANNEL
SELECTION
7
-13
AGC
OPERATION
AGO
1)
Each push
of the
UP
or
DN
(down)
SWITCH
on
the supplied
microphone
changes the
operating
frequency
one
increment
up
or
down
respectively.
2)
Holding
either
switch
down
changes the
operating
frequency
continuously
in
the
same manner
as
turning the
TUNING
CON-
TROL.
The
tuning
rate
must
be
set
with the
TUNING SPEED
SWITCH.
This
up/down
function
is
effective for
changing
your
operating
frequency
when
using the
VFO
mode,
or
when
using
the
ME-
MORY
CHANNEL
mode
with the
DFS SWITCH
pushed
IN.
1)
When
using the
MEMORY
CHANNEL
mode,
the
memory
chan-
nel
may
be
changed
with the
microphone
up/down
switches.
Also,
In
the
VFO
mode
with the
DFS SWITCH
pushed
IN,
the
displayed
memory
channel
number
may
be
changed
in
the
same
way.
2)
The
memory
channel or the displayed
memory
channel
number
changes every
two
seconds
If
the
microphone
switches
are
held
down.
The IC-751A
has
a
fast
attack/slow
release
AGC
system which
maintains the
peak
voltage of the
rectified IF signal
from
the
IF
amplifier
circuit
for
a brief
period of time. This
circuit
keeps
irritat-
ing
background
noise
from
being heard during the short pauses
in
speech.
The damping
effect
of the
AGC
therefore allows accurate
S-meter
readings to
be taken
of the
peak
IF
signal
strength.
1
)
For normal
SSB
reception,
select
the
SLOW
position.
2)
For
CW
or
AM
signals,
or
for
SSB
signals
with
short
interval
fading, select
the
FAST
position.
In
the
FAST
position,
the
time
constant of the
circuit
is
shortened.
3)
In
the
OFF
position,
the
AGC
circuit
is
deactivated
and
the
S-meter
gives
no
signal
strength readings.
In this
case,
the
RF
GAIN
CONTROL
is
useful
to
reduce the
receiver gain
when
strong
signals
are
received.
Adjustment
of
the
RF GAIN
CONTROL
affects
the
meter
reading
as
described
in
ltem(Dof
SECTION 3-1
FRONT
PANEL.
7
-14
PREAMP/ATT SWITCH OPERATION
•PREAMP
SWITCH OPERATION
Place the
PREAMP/ ATT SWITCH
on
the
top
panel
in
the
PRE
AMP
position
when
receiving
weak
signals.
An RF
preamplifier
is
inserted
in
the
receive
path
which
Increases receiver
sensitivity.
•ATTENUATOR
(ATT)
SWITCH
Place the
PREAMP/ ATT SWITCH
in
the
ATT
position
when
receiv-
OPERATION
ing
very strong
signals.
In
the
ATT
position,
the
RF
preamplifier
is
removed from
the
receive
path
and
a
20dB
attenuator
is
inserted.
This helps to reduce
interference.
Leave the
PREAMP/ATT
SWITCH
in
the
OFF
position for
normal
operation.
See
SECTION
3
-
3
for
the switch
location.
-
39
-
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