Elenco AM Radio Kit User Manual
Page 15
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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 10. Set the generator at a frequency of 1kHz,
turn the power ON and adjust the generator output
until the peaks of the sinewave at TP7 are clipped as
shown in Figure 11.
DISTORTION
Clipped
Crossover
Distortion
Figure 11 Figure 12
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
/