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Section III
Paragraphs 3-37 to 3-38
Model 415E
and: ±Ad = Shift in centimeters of the minimum
point when the short is used. Ad takes a positive
sign (+) if the minimum shifts toward the load.
Ad takes a negative sign(-)if the minimum shifts
toward the generator.
X«/2 = one-half guide wavelength, i.e., the
distance in centimeters between two adjacent volt¬
age minima.
Note
The above calculations are based on the as¬
sumption that no losses occur in the trans¬
mission line.
It is assumed that the char¬
acteristic line impedance,
Zq,
is resistive.
3-37. SMITH CHART EXPLANATION.
3-38. When data is obtained from a slotted line sys¬
tem, one of the best aids for determining impedance
is the Smith Chart. * A Smith Chart with an example
(see Paragraph 3-39) is shown in Figure 3-10.
The
values of resistance and reactance are based on a nor¬
malized value obtained by dividing the actual value by
the characteristic impedance, Zq, of the line.
Thus
if
Z
= 5 +• j 25 ohms and if
Zq
= 50 ohms, then Zjg =
0.1 + j 0.5.
On the Smith Chart, the circles which
are tangent to the bottom of the chart are for a con¬
stant, normalized resistance; lines curvingtothe right
from center are the normalized positive reactance
components; lines curving to the left from center are
the normalized negative reactance components; the
straight line forming the vertical diameter is aline of
zero reactance; the lower half of the zero reactance
line (marked 1 through 50) also represents the stand¬
ing wave ratio line.
* Smith, P. H. , "Transmission - Line Calculator, "
Electronics, Jan. 1939, McGraw-Hill.
3-8
Figure 3-10.
Example for Use of Smith Chart
02152-2
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