|
| |
Back
PERCENT OF MODULATION IN AN AM WAVE - Continued | Up
Neets Module 12-Modulation Principles | Next
Envelope Development from Vectors |
1-50
If Em and Ec in the equation are assumed to represent peak-to-peak values, the following formula
results:
Since the peak-to-peak value of E
m
in figure 1-42 is emax
-
emin, we can substitute as follows:
Also, since the peak-to-peak value of the carrier Ec is 2 times eo, we can subsititute 2eo for Ec as
follows:
Linear vertical distance represents voltage on the screen of a cathode-ray tube. Vertical distance units
can be used in place of voltage in equations. Thus, if only the percent of modulation is required, the
oscilloscope need not be calibrated and the actual circuit voltages are not required. In figure 1-42, emax
represents 600 volts (3 large divisions); emin is 200 volts (1 division); and eo is 400 volts (2 divisions).
Using the equation and the dimensions of the screen pattern, you can figure the percent of modulation as
follows:
When eo of the equation is difficult to measure, an alternative solution can be obtained with the
equation below:
VECTOR ANALYSIS OF AN AM WAVE.—You studied earlier in this chapter that the
modulation envelope results when the instantaneous sums of the carrier and sideband voltages are plotted
with respect to time. An attempt to add these three voltages, point-by-point, would prove to be a huge
task. The same end result can be obtained by using a rotating vector to represent each of the three
|
