5.7.0 MODULATION ACCEPTANCE BANDWIDTH
1.
Perform the I2 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 I2 dB
SINAD level, to double the voltage. For example,
0.35uV increased 6
dB=0.7uV.
3.
Turn the
"I
KHz Lvl" control clockwise to increase
the deviation until the
SINAD level returns to I2
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.
RF PRESELECTDR
SHAPE
AIID
BANDWIDTH
DID
\lwt:ISI\IAD/
Rf
h/Out
--
Ext
.......
-
Out
Hod
Out
Ext
Hod "
0 0 0 0 0
K.ECTIDN
fl.
TER
II..ECTIIN
FRE0
SIJNM.
FIGURE
5.4-
PROBE SETUP
5.8.0
RF PRESELECTOR
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.
5-4
I. Connect the service monitor's "Antenna" to the
antenna connector
of
the receiver under test. Con-
nect the
"Vert/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, "Function" to "Hi Gen",
modulation to "CW", and the scope sweep control
to
"IOOuS/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.
D
I
'Monl:M.:I:!OMHztl
E:J
t>.v •
fnq
•
0.0
ICHt
Errar
0.00
ICHt
YwtiStc""/
Rf In/out Dlstii>IIM
0 Q
Ext
HoriE
Domod
Out
0 0
Hod
Out
Ext Hod
In
0 0
LfiiT
lJNDER
TEST
FIGURE
5.5-
FREQUENCY ADJUSTMENT SETUP
5.9.0
RECEIVER FREQUENCY ADJUSTMENT
I. 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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