Audio Power Output Test; Audio Frequency Response - Motorola R-2200 Operator's Manual

5. Return "Gen On/Off" switch to on. Increase the RF
Level by adjusting the step attenuator and "RF Ver-
nier" controls until the receiver just unsquelches.
a. On the LCD, read minimum squelch sensitivity
as uV or dBm. This is the threshold squelch sen-
sitivity of the receiver.
b. Determine the tight squelch sensitivity of there-
ceiver by repeating steps 4 and 5 with the receiv-
er's squelch control set to maximum tightness.
6. Enable the receiver's PL/DPL squelch circuit. Fully
open the carrier squelch control. Increase the RF
level from minimum, as in step 5, until the receiver's
squelch just opens. On the right LCD, read the
coded squelch sensitivity in u V or dBm.
5.5.0 AUDIO POWER OUTPUT TEST
1. Referring to figure 5.2, set "Function" switch to
"Gen" and modulation to "FM". Enter the RF fre-
quency and PL code.
2. Adjust the step attenuator and "RF" Vernier' con-
trols to 1000uV (-47 dBm). Adjust the "1KHz Lvl"
control to 600Jo of the rated deviation on the KHz
scale. Use the "RF In/Out" connector for this test.
3. Select "DVM" "AC" function.
4. Connect a suitable resistive load that can dissipate
the receiver's rated audio output, in place of the
speaker. (If the receiver is using a "floating" or
"bridge" output amplifier, connect a 1 : 1 isolation
transformer across the load resistor).
5. Connect a scope probe to the service monitor's
"Vert/SINAD/Dist" input connector and clip the
probe across the load resistor or to the isolation
transformer.
6. Connect "RF In/Out" to the receiver's antenna
port. Adjust the receiver's volume control for the
highest voltage reading on the DVM AC scale which
does not have clipping or other distortion in excess
of the radio's spec as viewed on the oscilloscope.
7. Calculate the audio power by the following
formula:
Power Out (Watts)=
(AC volts)2
Load Resistance (ohms)
8. If the receiver does not produce rated audio power
output, use the service monitor's oscilloscope and a
scope probe to trace through the audio stages and
locate the problem.
5.6.0 AUDIO FREQUENCY RESPONSE
1. Use the keyboard to enter the frequency and
PL/DPL code (if any) of the receiver under test.
2. Set the "Function" switch to "Gen" and modulation
to "FM", step attenuator and vernier controls to
1000uV (-47 dBm).
3. Select and set Tone A to 1000Hz. Set modulation
switch to "Cant".
5-3
4. Adjust the "Code Synth Lvl" control for 20% of
rated deviation on the Dev scale, for example:
1 KHz in a 5KHz system. Select "DVM" on the left
LCD and "AC" volts.
5. Connect the service monitor's "RF In/Out" port to
the receiver's antenna port. 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 to ground.
6. Adjust the receiver's volume control to obtain a ref-
erence level reading on the AC volts scale which is
free of clipping at any frequency within the 300 to
3000 Hz band. Return to 1 kHz and note this read-
ing as the reference level (in AC volts).
7. Refer to the audio response curve in the receiver's
service manual. Change the Tone A frequency on
the tone display LCD to the value for each point on
the curve to be measured.
8. Maintain FM deviation at 20% of the rated devia-
tion, as set in step 4. Note the audio level at each
frequency. The level in dB must be calculated as
20
X
log(V /VREF) where VREF is the voltage re-
corded in step 6.
9. EIA RS-204C specifies the frequency response for
NBFM receivers over the range of 300Hz to 3000
Hz as follows:
a. Audio response for receivers using loudspeakers
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 headphones
or telephone 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. Plot the resulting values using 0 dB as the reference
and compare them with the 6 dB per octave curve in
your receiver's service manual or with the EIA
specification as shown on figure 5.3.
-6 dB/OCT
1\VE
SLOPE
300Hz
1000Hz
FIGURE 5.3-RECEIVER AUDIO
FREQUENCY RESPONSE
+9.Sd9