HP 415E - Page 15

Section ПІ
Рагасгарһв 3-97 іо 3-38
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.
A d takes a negative sign(-)if the minimum shifts
toward the generator.
8/2 = 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, Zp, 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
AB 9 еы
аСТ В
of SOMME о
TOETER
Model 415E
is the Smith Chart. * A Smith Chart with ап example
(see Paragraph 3-39)is shown in Figure 3-10. The
values ofresistance andreactance are basedon a nor-
malized value obtained by dividing the actual valueby
the characteristic impedance, Zp, of the line. Thus
if Z з 5 + j 25 ohms and if 20 =o ohms, then Zw =
0.1 + j 0.5. On the Smith Chart, the circles which
are tangent to the bottom of the chart are for а 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.
ж Smith, P. H., "Transmission - Line Calculator, "
Electronics, Jan. 1939, McGraw-Hill.
xu
Ec
m
M
v
T
> їз
Сас
оя
EN
АА
410 TOWARD Z ZŠ
4156 -B-2
Figure 3-10. Example for Use ої Smith Chart
3-8
02152-2