<s>
Analog	B-Protocol
transmission	I-Protocol
is	O
a	O
transmission	O
method	O
of	O
conveying	O
information	O
using	O
a	O
continuous	O
signal	O
which	O
varies	O
in	O
amplitude	B-Application
,	O
phase	O
,	O
or	O
some	O
other	O
property	O
in	O
proportion	O
to	O
that	O
information	O
.	O
</s>
<s>
It	O
could	O
be	O
the	O
transfer	O
of	O
an	O
analog	O
signal	O
,	O
using	O
an	O
analog	B-Application
modulation	I-Application
method	O
such	O
as	O
frequency	B-Application
modulation	I-Application
(	O
FM	B-Application
)	O
or	O
amplitude	B-Device
modulation	I-Device
(	O
AM	O
)	O
,	O
or	O
no	O
modulation	B-Application
at	O
all	O
.	O
</s>
<s>
Some	O
textbooks	O
also	O
consider	O
passband	B-Algorithm
data	O
transmission	O
using	O
a	O
digital	O
modulation	B-Application
method	O
such	O
as	O
ASK	O
,	O
PSK	O
and	O
QAM	O
,	O
i.e.	O
</s>
<s>
a	O
sinewave	O
modulated	B-Application
by	O
a	O
digital	O
bit-stream	O
,	O
as	O
analog	B-Protocol
transmission	I-Protocol
and	O
as	O
an	O
analog	O
signal	O
.	O
</s>
<s>
Baseband	B-Algorithm
data	O
transmission	O
using	O
line	B-Protocol
codes	I-Protocol
,	O
resulting	O
in	O
a	O
pulse	O
train	O
,	O
are	O
always	O
considered	O
as	O
digital	O
transmission	O
,	O
although	O
the	O
source	O
signal	O
may	O
be	O
a	O
digitized	O
analog	O
signal	O
.	O
</s>
<s>
Analog	B-Protocol
transmission	I-Protocol
can	O
be	O
conveyed	O
in	O
many	O
different	O
fashions	O
:	O
</s>
<s>
There	O
are	O
two	O
basic	O
kinds	O
of	O
analog	B-Protocol
transmission	I-Protocol
,	O
both	O
based	O
on	O
how	O
they	O
modulate	O
data	O
to	O
combine	O
an	O
input	O
signal	O
with	O
a	O
carrier	O
signal	O
.	O
</s>
<s>
The	O
two	O
techniques	O
are	O
amplitude	B-Device
modulation	I-Device
(	O
AM	O
)	O
,	O
which	O
varies	O
the	O
amplitude	B-Application
of	O
the	O
carrier	O
signal	O
,	O
and	O
frequency	B-Application
modulation	I-Application
(	O
FM	B-Application
)	O
,	O
which	O
modulates	O
the	O
frequency	O
of	O
the	O
carrier	O
.	O
</s>
<s>
Most	O
analog	B-Protocol
transmissions	I-Protocol
fall	O
into	O
one	O
of	O
several	O
categories	O
.	O
</s>
<s>
Early	O
telecommunication	O
devices	O
utilized	O
analog-to-digital	O
conversion	O
devices	O
called	O
modulator/demodulators	O
,	O
or	O
modems	B-Application
,	O
to	O
convert	O
analog	O
signals	O
to	O
digital	O
signals	O
and	O
back	O
.	O
</s>
<s>
The	O
analog	B-Protocol
transmission	I-Protocol
method	O
is	O
still	O
very	O
popular	O
,	O
in	O
particular	O
for	O
shorter	O
distances	O
,	O
due	O
to	O
significantly	O
lower	O
costs	O
and	O
complex	O
multiplexing	O
and	O
timing	O
equipment	O
is	O
unnecessary	O
,	O
and	O
in	O
small	O
"	O
short-haul	O
"	O
systems	O
that	O
simply	O
do	O
not	O
need	O
multiplexed	O
digital	O
transmission	O
.	O
</s>
<s>
Recently	O
,	O
some	O
nations	O
,	O
such	O
as	O
the	O
Netherlands	O
,	O
have	O
completely	O
ceased	O
analog	B-Protocol
transmissions	I-Protocol
(	O
analog	O
switch-off	O
)	O
on	O
certain	O
media	O
,	O
such	O
as	O
television	O
,	O
for	O
the	O
purposes	O
of	O
the	O
government	O
saving	O
money	O
.	O
</s>
