Marconi Instruments 2955 - Page 44

OPERATION
(20)
If
required,
set the
modulation
value
increment/'decremenr
by
selecting
A
JNCR
(T)
and
entering
the step
size.
e.g.
for a 4
kHz step, enter
the following:--
LEVEL
fNCR
4
1
FM
--
In
the
example,
both
LEVEL
and
FM
may
be omitted since they
have
been
pre-
viously
entered
in
(19),
(21)
Adjust
the
modulation
value
as for
(9).
Modulation
on/off
(22)
Switch
the
modulation
(both internal
and
external,
if
applied)
on
or
off
as
required
using
the
MOD
ON-OFF
key
The
off
condidon
is shown
in
reverse
field
on
the
display.,
External
modulation
(single
or two
tone)
(23)
To set
the
external
modulation,
connect the signal to the AF INPUT
socket
(2l)..
Select
SCOPE
(2^
and
observ'e
the
signal. Set the frequency
and
adjust
the
level
in
accordance
with
the
data
in the
‘Modulation
Section’ of
‘Performance Data’,
Chap,
1.
(24)
Connect
the
modulating
signal
to
EXT MOD
ENPLT
(23)
. For two tone modula-
tion,
the
external
modulation
then
adds
to the internal
modulation. To
switch off the
internal
modulation
while
retaining
external
modulation,
enter
0
kHz for FM,
Q%
for
AM or 0
radians
for
OM.
internal
two
tone
modulation
UM
Press
TOinES
0
to
cispiay
tne
TONES
STANDARD MEND.
Press
the
MODE
key
0
indicated
by
the
SUB-AUDBLE arrow.
R.X SLB-AUDIBLE TONE
is
displayed
together
with
the
current
sub-audible
tone frequency,
level
and
modula-
tion,
As
shown
on the
screen,
the
signal
generator
is
now modulated by
a fixed
1
kHz tone.
(26)
Press
the
key
arrowed
by
FREQLDNCY
and set the second,
variable
frequency
using
the
keypad
(J),
ending
with
the
frequency
terminator
(0
.
’
Press
the
key arrowed
by
MOD
LEVEL
and set the
level
using
the
keypad
(i),
ending
with
the
level
terminator
(28)
Press
the
key
arrowed
by SEND
TONE to
generate
the sub-audible
tone
the
return to
RECEIVER
TEST.
SAT is
displayed
in reverse
field
against
the
1 kPL
modulation
frequency.
(29)
To
return
to
single tone modulation,
press TONES
0
and
then
the
key
arrowed
by
SUB-
AUDIBLE. Press the
key
arrowed
by
STOP
TONE
and
then
return
to RECEIVER
TEST.
3-20
46881-622N
Apr.
83