Transmitter Audio Distortion; Transmitter Audio Frequency Response; Ammodulationtest - Motorola R-2200 Operator's Manual

+9.5.&
300Hz 1000Hz 2500Hz 3000Hz
FIGURE 5.9-AUDIO FREQUENCY RESPONSE
5.11.0 TRANSMITTER AUDIO DISTORTION
1. Before starting this test, adjust the transmitter's
IDC to specification.
2. Connect the service monitor to the transmitter, as
shown in figure 5.8. Observe caution on page 5-5.
3. Turn off the modulation. Disable PL or DPL. Set
"Function" to "Pwr Mon" (or "Pwr Mon/ Anlzr
On").
4. Key the transmitter and adjust the "1KHz Lvl" con-
trol for 600Jo of full-rated transmitter deviation on
the left LCD.
5. Select "Dist'' on the left LCD. Read transmitter OJo
distortion from the display. Unkey the transmitter.
5.12.0 TRANSMITTER AUDIO FREQUENCY
RESPONSE
1. As shown in Figure 5.7, connect the service moni-
tor's "RF In/Out" port to the transmitter's RF out-
put and the "Vert/Sinad/Dist" input jack to the
"Mod Out" jack through a BNC tee connected to
the transmitter's microphone audio input. Disable
PL and DPL.
2. Select "DVM" in the left LCD and set the source
switch to "AC". Set "Function" to "Pwr Mon",
"FM", attenuator to -40 dB modulation to "Cont"
and "Tone A". Enter the transmitter frequency.
Turn off the "1 KHz Lvl" and "Ext Lvl". When us-
ing an R-2400, the "Function" switch may be set to
"Pwr Mon/ Anlzr On" to observe the occupied
bandwidth of the modulated carrier. Set "Disp" to
.01 MHz/Div.
3. Enter the required Tone A frequency.
4. Set "Function" to "Pwr Mon" (or "Pwr Mon/ Anlzr
On"). Key the transmitter and adjust "Code Synth
Lvl" to provide 300Jo of rated transmitter deviation.
5. Note both the transmitter MIC audio input level
and the test frequency, for later use.
6. Repeat the above procedure, adjusting "Code Synth
Lvl" to maintain 30% of rated deviation, for each
modulation frequency to be tested.
5-7
7. Plot the data points obtained above in dB relative to
the 1 KHz level and compare with the transmitter's
specifications. EIA RS-152B specifies that a trans-
mitter's frequency response be within
+
1 dB or -3
dB of a
+
6 dB per octave pre-emphasis from 300 to
3000 Hz (6 dB per octave roll-off allowed between
2500 and 3000Hz). Refer to figure 5.9.
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AM TRANSMITTER
FIGURE 5.10-AM MODULATION TEST SETUP
5.13.0 AM MODULATION TEST
1. Connect the service monitor's "RF In/Out" to the
output connector of the transmitter under test, as
shown in figure 5.1 0. Set "Function" to "Pwr Mon",
"AM". Observe caution in basic transmitter tests
section.
2. Connect the service monitor's "Mod Out" connector
to "Vert/Sinad/Dist" and to the transmitter's mi-
crophone input using a BNC tee connector.
3. Set left LCD to "DVM" and the "AC" voltmeter
function.
4. Adjust the "1 KHz Lvl" control to provide the
proper input signal level to the transmitter. Refer to
the transmitter's service manual to obtain the value
for this level.
5. Key the transmitter. Read OJo AM on the left LCD
display.