<s>
QAM	B-Device
is	O
a	O
digital	B-Application
television	I-Application
standard	O
using	O
quadrature	B-Device
amplitude	I-Device
modulation	I-Device
.	O
</s>
<s>
It	O
is	O
the	O
format	O
by	O
which	O
digital	B-Device
cable	I-Device
channels	O
are	O
encoded	O
and	O
transmitted	O
via	O
cable	O
television	O
providers	O
.	O
</s>
<s>
QAM	B-Device
is	O
used	O
in	O
a	O
variety	O
of	O
communications	O
systems	O
such	O
as	O
Dial-up	O
modems	O
and	O
WiFi	O
.	O
</s>
<s>
In	O
cable	O
systems	O
,	O
a	O
QAM	B-Device
tuner	I-Device
is	O
linked	O
to	O
the	O
cable	O
in	O
a	O
manner	O
that	O
is	O
equivalent	O
to	O
an	O
ATSC	B-Device
tuner	I-Device
which	O
is	O
required	O
to	O
receive	O
over-the-air	O
(	O
OTA	O
)	O
digital	O
channels	O
broadcast	O
by	O
local	O
television	O
stations	O
when	O
attached	O
to	O
an	O
antenna	O
.	O
</s>
<s>
Most	O
new	O
HDTV	O
digital	B-Application
televisions	I-Application
support	O
both	O
of	O
these	O
standards	O
.	O
</s>
<s>
QAM	B-Device
uses	O
the	O
same	O
6MHz	O
bandwidth	O
as	O
ATSC	O
,	O
using	O
a	O
standard	O
known	O
as	O
ITU-T	O
Recommendation	O
J.83	O
Annex	O
B	O
(	O
"	O
J.83b	O
"	O
)	O
.	O
</s>
<s>
QAM	B-Device
is	O
a	O
modulation	O
format	O
and	O
does	O
not	O
specify	O
the	O
format	O
of	O
the	O
digital	O
data	O
being	O
carried	O
.	O
</s>
<s>
However	O
,	O
when	O
used	O
in	O
the	O
context	O
of	O
US	O
digital	B-Device
cable	I-Device
television	I-Device
,	O
the	O
format	O
of	O
the	O
data	O
transmitted	O
using	O
this	O
modulation	O
is	O
based	O
on	O
ITU-T	O
J.83	O
Annex	O
B	O
(	O
"	O
J.83b	O
"	O
)	O
.	O
</s>
<s>
This	O
is	O
in	O
contrast	O
to	O
DVB-C	B-Device
which	O
is	O
also	O
based	O
on	O
QAM	B-Device
modulation	O
,	O
but	O
uses	O
a	O
DVB-based	O
data	O
format	O
which	O
is	O
incompatible	O
with	O
North	O
American	O
receivers	O
.	O
</s>
<s>
QAM	B-Device
is	O
a	O
parallel	O
form	O
of	O
modulation	O
that	O
transmits	O
two	O
independent	O
signals	O
at	O
a	O
symbol	O
rate	O
that	O
is	O
near	O
,	O
but	O
less	O
than	O
,	O
the	O
bandwidth	O
of	O
6MHz	O
.	O
</s>
<s>
The	O
two	O
can	O
be	O
related	O
by	O
the	O
fact	O
that	O
a	O
VSB	O
signal	O
can	O
be	O
shown	O
to	O
be	O
a	O
form	O
of	O
offset	O
QAM	B-Device
modulation	O
where	O
one	O
of	O
the	O
two	O
independent	O
signals	O
is	O
delayed	O
by	O
1/2	O
a	O
symbol	O
duration	O
.	O
</s>
<s>
The	O
8-VSB	O
modulation	O
in	O
the	O
ATSC	O
system	O
corresponds	O
with	O
the	O
64-QAM	B-Device
modulation	O
of	O
J.83b	O
.	O
</s>
<s>
In	O
a	O
6MHz	O
channel	O
,	O
the	O
data	O
rate	O
is	O
at	O
most	O
36	O
Mbit/s	O
(	O
for	O
64-QAM	B-Device
or	O
8-VSB	O
)	O
;	O
the	O
8-VSB	O
ATSC	O
achieves	O
a	O
data	O
rate	O
of	O
19.3926	O
Mbit/s	O
while	O
the	O
64-QAM	B-Device
J.83b	O
achieves	O
a	O
data	O
rate	O
of	O
26.970	O
Mbit/s	O
.	O
</s>
<s>
In	O
addition	O
,	O
J.83b	O
defines	O
a	O
popular	O
256-QAM	B-Device
mode	O
that	O
achieves	O
a	O
data	O
rate	O
of	O
38.8	O
Mbit/s	O
.	O
</s>
<s>
Many	O
cable	O
providers	O
offer	O
few	O
or	O
no	O
details	O
about	O
unencrypted	O
QAM	B-Device
channels	O
.	O
</s>
<s>
It	O
is	O
also	O
common	O
for	O
cable	O
providers	O
to	O
falsely	O
insist	O
that	O
a	O
set-top	O
box	O
from	O
the	O
cable	O
company	O
is	O
required	O
to	O
watch	O
all	O
digital	B-Device
cable	I-Device
channels	O
,	O
including	O
unencrypted	O
channels	O
,	O
even	O
though	O
some	O
unencrypted	O
QAM	B-Device
channels	O
may	O
be	O
distributed	O
via	O
their	O
system	O
.	O
</s>
<s>
QAM	B-Device
channels	O
may	O
move	O
without	O
notification	O
and	O
some	O
channels	O
may	O
have	O
strange	O
numbering	O
schemes	O
when	O
received	O
on	O
a	O
non-proprietary	O
set-top	O
box	O
.	O
</s>
<s>
In	O
North	O
American	O
digital	O
video	O
,	O
a	O
QAM	B-Device
tuner	I-Device
is	O
a	O
device	O
present	O
in	O
some	O
digital	B-Application
televisions	I-Application
and	O
similar	O
devices	O
which	O
enables	O
direct	O
reception	O
of	O
digital	B-Device
cable	I-Device
channels	O
without	O
the	O
use	O
of	O
a	O
set-top	O
box	O
.	O
</s>
<s>
An	O
integrated	O
QAM	B-Device
tuner	I-Device
allows	O
the	O
free	O
reception	O
of	O
unscrambled	O
digital	O
programming	O
sent	O
"	O
in	O
the	O
clear	O
"	O
by	O
cable	O
providers	O
,	O
usually	O
local	O
broadcast	O
stations	O
,	O
cable	O
radio	O
channels	O
,	O
or	O
in	O
the	O
case	O
of	O
providers	O
which	O
have	O
transitioned	O
to	O
do	O
so	O
,	O
Public-access	O
television	O
cable	O
TV	O
channels	O
.	O
</s>
<s>
The	O
FCC	O
mandates	O
that	O
all	O
new	O
TVs	O
sold	O
in	O
the	O
US	O
must	O
include	O
an	O
ATSC	B-Device
tuner	I-Device
,	O
but	O
there	O
are	O
no	O
requirements	O
for	O
QAM	B-Device
tuning	O
functionality	O
.	O
</s>
