Elenco AM/FM Radio Kit - Manual (Page 14)

-13-
MAXIMUM POWER OUTPUT
The maximum power output before distortion due to
“clipping” can be calculated using the voltage Vclp
obtained in the Distortion Step as follows:
Vpeak (Vp) = Vclp/2
Vroot mean squared (Vrms) = Vp x 0.7
Max power out = (Vrms) 2 /8 ohms = (Vclp x 0.35) 2 /8
Maximum power output should be greater than 200
milliwatts.
EFFICIENCY
Figure 10
Clipped
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. Efficiency can then be calculated as
follows: Eff = Max audio power/Battery power. It is
best to use a power supply (if available) to prevent
supply voltage from changing during these
measurements.
Connect the generator, oscilloscope, power supply
(or battery) and current meter as shown in Figure 11.
Set your current meter to read 1 amp DC. Turn the
power ON and rotate the volume control to
maximum. Slowly increase the amplitude of the
audio generator until the output is clipped as shown
in Figure 10. Record Vclp here:
Vclp = _________ Vpp.
This should be equal to Vclp in the Distortion Step.
Record the DC current drawn from the 9 volt supply
here:
Current (I) max = ________ A.
Measure the supply voltage and record the V supply
here:
V supply = ________ volts.
Turn the power OFF.
Calculate the maximum power output as done in the
Maximum Power Output Step.
Record your answers on the following page.