Attenuators 775

When the impedances are unequal values, the resis-
tors are calculated with the following equations:

(22-36)

(22-37)

(22-38)

where,
R 1 and R 3 are shunt resistors in ohms,
R 2 is the series resistor in ohms,
Z 1 is the input impedance in ohms,
Z 2 is the output impedance in ohms,

.

The values of K, K^2 , and g are taken from Table 22-1.

An O-type attenuator is a balanced S attenuator. The
circuit element values may be obtained by first calcu-
lating for a S configuration and then dividing the series
resistor and placing half in each side of the line, Fig.
22-15. The shunt resistors remain the same value.

22.2.6 U Attenuators

U attenuators, Fig. 22-16, may be of a symmetrical or
balanced-type configuration and are useful for matching
a high impedance to a low impedance. The impedance
match is of first importance, the loss being secondary.

For a symmetrical configuration to work between

unequal impedances when the impedance match of Z 1 is

important, the resistors may be calculated as follows:

(22-39)

(22-40)

where,

R 1 is the series resistor in ohms,

R 2 is the shunt resistor in ohms,

Z 1 is the larger impedance in ohms,

Z 2 is the smaller impedance in ohms,

,

The value of K is taken from Table 22-1.

When the low impedance, Z 2 is to be matched the

equations are:

(22-41)

Figure 22-14. S and ' attenuators.

R 2

Z R 1 R 1 Z

Z 1 R 1 R 3 Z 2

R 2

p

p p

p

A. Between impedances of equal value.

B. Between impedances of unequal value.

R 1 Z 1 K

(^2) 1–
K^22 KS 1+–

©¹
̈ ̧
§·

R 2
Z 1 Z 2
2
=---------------- g
R 3 Z 2 K
(^2) 1–
K^22 K
S
–1--- -+

©¹
̈ ̧
̈ ̧
§·

S is
Z 1
Z 2

Figure 22-15. Balanced S or O attenuator.
Figure 22-16. A U pad configuration for operation
between impedances of unequal value.
Z 1 Z 2
Z (^1) R Z 2
1
R 1 R 1
R 3
R 2
2
p
p
p
p
p
p
p
p
B. Between impedances of unequal value.
A. Between impedances of equal value.
R 2
2
R 2
2
R 2
2
p
p p
p
Z 1 Z 2
R 1
R 2
R 1
R 1
Z 1
2 S
----- -KS 1–
K

©¹
= §·
R 2
Z 1
S
-----^1
KS–
= ©¹§·-------------
S is
Z 1
Z 2

R 1
Z 1
2 S
=----- - KS–