this way, the resistance of the line is cut in half, thus extending its useful range. The talking ranges under various
operating conditions of a single pair and of a twin pair (of wires) are shown in Table #1 below.
The range for wire laid on the ground is lower than
the range for the same wire strung above the ground.
Wetness (rain or, sometimes, heavy dew) greatly
reduces the range of all the wires when they are used
without insulators.
TABLE #1
58.
Characteristics of Transmission Line.
a. Electrical length of line. An important characteristic of a transmission line, significant in determining its
behavior, is its electrical length. The electrical length expresses the relationship between the length of a line and the
wavelength of the signal being transmitted over the line. The wavelength of an electrical wave is defined as the velocity
with which the wave is traveling along the conductor divided by the frequency of the signal, or
The velocity of propagation at 1,000 cycles per second on open-wire lines varies from 176,000 to 180,000 miles per
second, approximately; on nonloaded toll cables, it varies from 47,600 to 65,300 miles per second, approximately, for the
sizes customarily used.
(1) Short lines. A short line may be defined as one in which the length of the line is considerably
shorter than the wavelength of the transmitted signal. A, figure 53A, represents a line that is electrically short.
This line is 1 loop mile in length. The signal applied to the sending end of the line has a frequency
of 1,000 hertz; therefore, if the velocity is assumed to be 180,00 miles per second, the wavelength of
the signal is 180 miles, or the 1-mile line is 1/180 of a wavelength electrically. A line 1 mile long having
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