Elenco AM Radio Kit - Manual (Page 21)

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Figure 18
10
μF
GND
TP10
Output Adjust
Generator
GND
TP10
Oscilloscope
Probe
Measure the maximum voltage peak to peak when
clipping first occurs and record that value here:
Vclp = _______ Vpp.
The maximum power output before distortion due to
“clipping” can be calculated using the voltage Vclp
obtained in step 3 as follows:
Vpeak (Vp) = Vclp/2
Vroot mean squared (Vrms) = Vp x .7
Max power out = (Vrms)
2 /8 ohms = (Vclp x .35) 2 /8
Maximum power output should be greater than 200
milliwatts.
MAXIMUM POWER OUTPUT
Connect the generator and oscilloscope as shown in
Figure 18. Set the generator at a frequency of 1kHz, turn
the power ON and adjust the generator output until the peaks of the sinewave at TP8 are clipped as shown in
Figure 9A.
DISTORTION
By measuring the DC power taken from the battery at
the maximum power output level, the efficiency to the
Audio Amplifier can be calculated. Power from the
battery is equal to the current taken from the battery
times the voltage of the battery during maximum power output. It is best to use a power supply to prevent battery
voltage from changing during this measurement.
Efficiency can then be calculated as follows:
Eff =
EFFICIENCY
Max power output
Battery power
/