Motorola R-2400 Operator's Manual page 38

5.7.0
MODUTATION ACCEPTANCE BANDWIDTH
l.
Perform the
12
dB SINAD Sensitivity test with
the
service
monitor
in
the
same set-up as shown in
figure
5
.2.
2.
Increase
the RF output level 6 dB
above
the
12
dB
SINAD level, to
double the voltage. For
example,
0.35uV increased 6
dB
-
0.7uV.
3.
Turn the
"l
KHz Lvl" control
clockwise
to
increase
the deviation
until
the SINAD level returns
to
12
dB.
Read the amount
of
deviation on
the
display
as
the modulation
acceptance bandwidth
of
the
re-
ceiver.
4.
A
typical modulation
acceptance
value
for a
re-
ceiver
is 7 KHz. Refer
to
the specification
for
the
specific receiver under test. Any
loss
of modulation
acceptance
bandwidth indicates improper
align-
ment
or
a component failure
in
a
receiver's
IF
cir-
cuit.
l.
Connect the
service
monitor's "Antenna"
to
the
antenna connector
of
the receiver under test. Con-
nect the "Yert/SINAD/Dist" port to the RF
probe.
Connect the probe
to
the
first
available
low
im-
pedance
point following the
preselector,
as shown
in
figure
5.4.
2.
Disable the
receiver's
mixer injection.
3.
Set scope
to Ext Vert DC,'nFunction" to "Hi
Gen",
modulation to "CW",
and the
scope sweep
control
to
"lO0uS/div".
4.
Enter the approximate center frequency of the
pre-
selector.
Adjust the RF
Level (and
scope
vertical
controls)
to produce
a trace on the CRT
screen at
the
lowest readable
RF
level
to
minimize
the
possibility of
overloading the circuits being
tested.
5.
Using the Frequency Stepping function,
determine
at what
frequency the peak DC voltage occurs
on
the DVM or CRT.
6.
The
3
dB (.707 of peak) and
6
dB (.5 of peak)
band-
width points
can be checked
by
stepping either
up
or
down
in
frequency and observing the
change
in
DC level from the RF probe.
PF PRESETECTOR S]IAPE
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FIGURE s.4-PROBE
SETUP
5.E.0
RF PRESELBCTOR SHAPE AND
BANDWIDTH
Use
this test to insure proper preselector alignment
for
multi-frequency receivers. Tune the
preselector for
greater rejection
of
an
interfering frequency from
near-
by transmitters.
FIGURE s.s_FREQUENCY ADJUSTMENT
SETUP
5.9.0 RECEMR
FREQUENCY ADJUSTMENT
l.
Connect
the
service
monitor to the
receiver under
test, as shown
in
figure
5.5.
2.
Set "Function" switch
to
"Sens
Mon" (or "Anlzr
Sens
Mon" on the
R-2400). Program the monitor
for
the local oscillator frequency.
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