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H
52005-301D
16
II
Ill
14
[\
II Ill
T
crminot ion switch
\
ot LOAD
EXT
\
I
I
1\
12
2:
10
1\
j
I
:%:
u
8
~
2:
Ill
i:
6
1\.
'
~
dB
r\
1\
....
~
4
0
Ill
1\
Ill
9
2
1.1.1
t-
1'.
Cl
41(
0
1-
......
~
r--
l'
I'
I'
-z
r-..
:
+-
!
;I
-4
I
ill
·I
·
3
·4
·5
z
3
4
7
10
-6
T'Cul
Fig.
4
Mismatch loss with
external
load
pective of the setting of the OUTPUT IMPEDANCE switch.
The internal
load
will be effecti\·e ly
in
parallel
with the
external load;
but
, if the latter
has
a high value, the
resu ltant
\'alue of the
combina
t
ion
will
differ
little from the matching value
.
This
bas
the adva
ntage
tha
t
it
can make
a
correction
for
mismatching unnecessary
in finding
the output
voltage,
a
nd
it
permits the
attenuation
to
be adjusted t
o low values without
effect on
the
input
meter r eading.
If
the
eA'ter-
nal load is not
ver
y
much
greater
in value than
the
output
impedance, a nd
the int er nal
load is
swit
ched
in, a
correction
must
be
added to fi
nd
the
voltage across
the
load.
The
\·oltage across
the load, V
0
=
(A
+
R
+
N)
dB
be low Vin
where
A, R, and Vin
a
r
e as defined
previously
and
N is the
correction, in dB, depending
on
the relation of
the
load
to the
output
impe-
dance (Fig.
5).
Nov. 79
Ill
Ill
0
......
4
""
I"
01
, , l l j
I'
t-.
......
2
3
Fig.
5
ll
llJ
TcrmiRatlon switch
It
LOAD
INT
4
5
7
10
20
30
4050
R_y;
Ro
Mismatch loss
with
internal load
10
00
Chap.
3
Page 1;:
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