<s>
Alternate-Phase	B-Protocol
Return-to-Zero	I-Protocol
(	O
APRZ	B-Protocol
)	O
is	O
an	O
optical	O
line	B-Protocol
code	I-Protocol
.	O
</s>
<s>
In	O
APRZ	B-Protocol
the	O
field	O
intensity	O
drops	O
to	O
zero	O
between	O
consecutive	O
bits	O
,	O
and	O
the	O
field	O
phase	O
alternates	O
between	O
neighbouring	O
bits	O
,	O
so	O
that	O
if	O
the	O
phase	O
of	O
the	O
signal	O
is	O
,	O
for	O
example	O
,	O
0	O
in	O
even	O
bits	O
(	O
bit	O
number	O
2n	O
)	O
,	O
the	O
phase	O
in	O
odd	O
bit	O
slots	O
(	O
bit	O
number	O
2n+1	O
)	O
will	O
be	O
ΔΦ	O
,	O
the	O
phase	O
alternation	O
amplitude	O
.	O
</s>
<s>
Return-to-zero	B-Protocol
can	O
be	O
seen	O
as	O
a	O
special	O
case	O
of	O
APRZ	B-Protocol
in	O
which	O
ΔΦ	O
=	O
0	O
,	O
while	O
Carrier-Suppressed	B-Protocol
Return-to-Zero	I-Protocol
(	O
CSRZ	B-Protocol
)	O
can	O
be	O
viewed	O
as	O
a	O
special	O
case	O
of	O
APRZ	B-Protocol
in	O
which	O
ΔΦ	O
=	O
π	O
(	O
and	O
the	O
duty	O
cycle	O
is	O
67%	O
,	O
at	O
least	O
in	O
the	O
standard	O
form	O
of	O
CSRZ	B-Protocol
)	O
.	O
</s>
<s>
APRZ	B-Protocol
can	O
be	O
used	O
to	O
generate	O
specific	O
optical	O
modulation	O
formats	O
,	O
for	O
example	O
,	O
APRZ-OOK	O
,	O
in	O
which	O
data	O
is	O
coded	O
on	O
the	O
intensity	O
of	O
the	O
signal	O
using	O
a	O
binary	O
scheme	O
(	O
light	O
on	O
=	O
1	O
,	O
light	O
off	O
=	O
0	O
)	O
.	O
</s>
<s>
APRZ	B-Protocol
is	O
often	O
used	O
to	O
designate	O
APRZ-OOK	O
.	O
</s>
<s>
The	O
characteristic	O
properties	O
of	O
an	O
APRZ	B-Protocol
signal	O
are	O
those	O
to	O
have	O
a	O
spectrum	O
similar	O
to	O
that	O
of	O
an	O
RZ	O
signal	O
,	O
except	O
that	O
frequency	O
peaks	O
at	O
a	O
spacing	O
of	O
BR/2	O
as	O
opposed	O
to	O
BR	O
are	O
observed	O
(	O
where	O
BR	O
is	O
the	O
bit	O
rate	O
)	O
.	O
</s>
