Model
3642A/B
Operation
Modulation,
AM
(cont'd)
The
external
modulation
signal level should be adjusted to a 1 Vpk (0.707 Vrms)
sinewave
input
to the Signal
Generator
to
get
the
displayed AM depth.
With
an
external
1 Vpk signal applied,
the
Signal
Generator
modulates its
RF
output
to achieve
the
modulation
depth
setting. For example,
if
a 1 Vpk
external
modulation
source is
provided,
with
the
Signal Generator's AM
depth
set
to
50.0%
per volt,
the
output
has
50.0%
modulation
depth.
(If
the
source voltage is
reduced
to
0.5 Vpk,
and
no
other
settings are changed, the
output
has
25%
modulation
depth.)
If
the
HI
and
LO annunciators are
not
displayed,
then
the
external
modulation
signal
is
between 0.95 Vpk
and
1.05 VPk. The HI, LO
annunciators
only apply to sinewave
inputs.
The
HI, LO detectors
do
not
monitor
de voltage
input
levels.
External
Coupling
Anyone
of
the
following functions
can
be used to couple
the
external
AM/PULSE
INPUT
to
the
AM circuitry:
AC-Coupled
Source
•
(EXT
AC
1
This
function
selects the external,
ac-coupled
AM
source (displaying
the
EXT
and
AC
annunciators).
G
INT
+ (EXT AC)
((
SHIFT
I,
( EXT
AC
1 )
This
function
selects the external,
ac-coupled
AM
source
and
internal
AM
source
summed
together
(displaying the INT, EXT,
and
AC annunciators).
DC-Coupled
Source
o
CEXrps;]
This
function
selects the external,
dc-coupled
AM
source (displaying
the
EXT
and
DC annunciators).
•
INT
+ (EXT DC)
((
SHIFT
I, ( EXT
DC
1 )
This
function
selects
the
external,
dc-coupled
AM
source
and
internal
AM source
summed
together
(displaying the INT, EXT,
and
DC annunciators).
Rate
Determined
by
the
external modulation source frequency.
Depth
NOTE
External
modulation
frequency
is
not
monitored
by
the
Signal
Generator.
The Signal Genera tor's
modulation
frequency
display
refers to
the
internal
modulation oscillator only.
C8MJ
and
the
desired modulation
depth
(in % per volt).
The
modulation
depth
setting, when using
an
external
source, sets the
input
sensitivity
per
volt,
not
the
actual
depth. A
linear
relationship
exists between
the
AM
depth
setting
and
the
external
voltage applied (for voltages less
than
or
equal
to
approximately
1.2 Vpk).
3-99
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