Modulation Acceptance Bandwidth - Motorola R-2001D Operator's Manual

AUDIO FREQUENCY RESPONSE
1. Use the keypad to enter the frequency and PL/DPL code (if any) of the receiver under test.
2. Set FUNCTION to Generate FM, attenuator and Variable level controls to 1000 uV (-47 dBm).
3. Select tone memory display and set Tone A to 1000 Hz. Set MODULATION switch to Cont, Code Synthesizer Mode
to Tone A, and change DISPLAY to Gen/Mon Mtr.
4. Adjust the Code Synth Level control for 20% of rated deviation on the DEV KHZ scale, for example: 1 KHz in a
5KHz system. Change DISPLAY to DVM/Dist and select DVM AC function.
5. Connect the Analyzer's RF In/Out out to the receiver's antenna port. Push the Variable control in to select the RF
In/Out connector. Connect the Vert/Sinad/Dist input connector to the receiver's speaker output, using a scope
probe. If the speaker is "floating", use an isolation transformer to avoid shorting the output stage.
6. Adjust the receiver's volume control to obtain a reference level reading on the AC volts scale which is free of clipping
at any frequency within the 300 to 3,000 Hz band. Note this reading in dBm as the reference value.
7. Refer to the audio response curve in the receiver's Service Manual. Change the Tone A frequency on the tone
memory screen to the value for each point on the curve to be measured.
8. Maintain FM deviation at 20% of the rated deviation, as set in step 4. Change DISPLAY to DVM AC and read the
audio level at this frequency. Note this audio level. Repeat this step for each frequency tested.
9. EIA RS-204C specifies the frequency response for NBFM receivers over the range of 300 to 3000 Hz as follows:
a. Audio response for receivers using loud-speakers shall not vary more than
+
2 dB or -8 dB from a standard 6 dB
per octave curve, with reference taken as 1000 Hz.
b. Audio response for receivers using either headphones or telephones lines shall not vary more than
+
1 dB or -3 dB
from a standard 6 dB per octave curve, with reference taken at 1000 Hz.
10. Add or subtract the 1 KHz reference value from each reading taken in step 7. Plot the resulting values on a curve and
compare them with the 6 dB per octave curve in your receiver's Service Manual or with the standard EIA specifica-
tion RS-204C, as shown in figure 4-4.
MODULATION ACCEPTANCE BANDWIDTH
1. Perform the 12 dB SINAD Sensitivity Test with the Analyzer in the same setup as shown in figure 4-1. Note: It is
necessary to perform this test with the volume control set to 10% of rated audio output.
2. Increase the RF output level 6 dB above the 12 dB SINAD level, to double the voltage. For example, 0.35 uV in-
creased 6 dB=0.7 uV.
3. Turn the 1 KHz Level 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 receiver.
4. A typical modulation acceptance value for a receiver is 7 KHz. Refer to the specification for the specific receiver
under test. Any loss of modulation acceptance bandwidth indicates improper alignment or a component failure in a
receiver's IF circuit.
4-9