Impedance Measurement Rules - HP 415E Operating And Service Manual

Modei 415Е Section Ш
Paragraphs 3-33 to 3-36
IF MINIMUM SHIFTS 3/4,
LOAD EQUALS Z,: SWR
LOAD
MINIMUM
MINIMUM WILL SHIFT TO MINIMUM WILL SHIFT TO
THIS REGION IF LOAD THIS REGION IF LOAD
GENERATOR ІЗ INDUCTIVE LOAD
À À
ШЕ +52
IF MINIMUM DOES МОТ
SHIFT, LOAD EQUALS 2,// SWR RE
Figure 3-8. Impedance Measurement Rules Summary
3-32. LOAD IMPEDANCE MEASUREMENT.
3-33. GENERAL.
3-34. Slotted line techniques provide information to
allow calculation of a load impedance. The following
rules apply tothe indications givenbythe voltage min-
imum when the load is replaced by a short. Figure
3-8 summarizes and graphically presents these im-
pedance measurement rules. Whentheloadis replaced
by a short, then:
a. The shift in the minimum is never more than
31/4 wavelength.
b. If the minimum moves toward the load, the load
has a capacitive component,
c. É the minimum moves toward the generator, the
load has an inductive component.
d. H the minimum does not move, the load is com-
pletely resistive and has a normalized value of 1/swr.
e. If the minimum shifts exactly one-quarter wave-
ength, the loadis completely resistive and has a nor-
malized value equal to the swr.
f. The minimum will always be at a multiple of а
half wavelength from the load.
3-35. IMPEDANCE MEASUREMENT PROCEDURE.
3-36. The procedure for performing the actual im-
edance measurement witha slotted line is as follows:
a. Connect the load under test to the slotted line
section and measure the swr (see Paragraph 3-26 or
3-28). Also note the position of the probe carriage at
һе minimum.
b. Replace the load under test with a short.
с. Locate the minimum with the line shorted.
02152-2
d. Referring to Figure 3-9 and the following for-
mulas, compute the normalized load impedance:
Normalized 71, з EIE ATH талх
180° (+Ad)
Ag/
where X з
415Е-А-?
Figure 3-9. Shift of Minimum with Load and Short
8-7