
84-1
84.1 Introduction
It is oen the case in instrumentation and communication systems that an information-bearing signal
may not be in an optimal form for direct use. In such cases, the information-bearing signal may be used
to al
ter
so
me
ch
aracteristic
of a se
cond
sig
nal
mo
re
su
ited
to th
e
ap
plication
. i
s
pr
ocess
of al
tering
on
e
sig
nal
by me
ans
of an
other
is kn
own
as mo
dulation;
th
e
or
iginal
in
formation
is ca
lled
th
e
ba
seband
signal,
an
d
th
e
sig
nal
mo
dulated
by th
e
ba
seband
sig
nal
is te
rmed
th
e
ca
rrier
(b
ecause
it “c
arries”
th
e
in
formation
co
ntained
in th
e
ba
seband
sig
nal)
. Re
covery
of th
e
or
iginal
in
formation
re
quires
a su
itable
de
modu