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Chapter 7 Tutorial
Attributes of AC Signals
the balun effect and it reduces ground loops at higher frequencies.
Note that lower shield resistance causes the balun effect to become more
of a factor at lower frequencies. Therefore, coaxial cables with two or
three-braided shields are much better than those with single-braided or
foil shields.
To reduce errors due to ground loops, connect the function generator to
the load using a high-quality coaxial cable and ground it at the load
4
through the cable's shield. If possible, make sure the function generator
and the load are connected to the same electrical outlet to minimize
further differences in ground potential.
Attributes of AC Signals
The most common ac signal is a sine wave. In fact, any periodic signal
can be represented as the sum of different sine waves. The magnitude of
a sine wave is usually specified by its peak, peak-to-peak, or root-mean-
square (RMS) value. All of these measures assume that the waveform
has zero offset voltage.
V
Peak
V
= 0.707 V
RMS
Peak
V
Pk-Pk
1
T =
f
The peak voltage of a waveform is the maximum absolute value of all
points in the waveform. The peak-to-peak voltage is the difference
between the maximum and minimum. The RMS voltage is found by
summing the squares of the voltages of every point in the waveform,
dividing the sum by the number of points, and then taking the square
root of that quotient. The RMS value of a waveform also represents the
7
2
one-cycle average power in the signal: Power = V
/ R
. Crest factor
RMS
L
is the ratio of a signal's peak value to its RMS value and will differ
according to waveshape. The table below shows several common
waveforms with their respective crest factors and RMS values.
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