<s>
The	O
Motorola	O
AN/FPS	B-Algorithm
-23	I-Algorithm
was	O
a	O
short-range	O
early	B-Algorithm
warning	I-Algorithm
radar	I-Algorithm
deployed	O
on	O
the	O
Distant	O
Early	O
Warning	O
Line	O
(	O
DEW	O
Line	O
)	O
.	O
</s>
<s>
The	O
system	O
was	O
known	O
as	O
Fluttar	B-Algorithm
(	O
flutter	O
radar	O
)	O
during	O
its	O
development	O
at	O
the	O
Lincoln	O
Laboratory	O
,	O
and	O
this	O
name	O
was	O
widely	O
used	O
for	O
the	O
production	O
units	O
as	O
well	O
.	O
</s>
<s>
This	O
system	O
was	O
based	O
on	O
continuous	B-Algorithm
wave	I-Algorithm
radars	I-Algorithm
that	O
broadcast	O
a	O
signal	O
between	O
separate	O
transmitter	O
and	O
receiver	O
stations	O
.	O
</s>
<s>
Today	O
,	O
this	O
style	O
of	O
operation	O
is	O
known	O
as	O
a	O
forward	B-Algorithm
scatter	I-Algorithm
bistatic	I-Algorithm
radar	I-Algorithm
.	O
</s>
<s>
The	O
first	O
attempt	O
was	O
made	O
by	O
the	O
Air	O
Force	O
Cambridge	O
Research	O
Laboratory	O
,	O
who	O
surmised	O
that	O
using	O
lower	O
frequencies	O
in	O
the	O
VHF	B-Algorithm
range	O
might	O
mitigate	O
the	O
problem	O
due	O
to	O
the	O
lower	O
Rayleigh	O
scattering	O
cross-section	O
as	O
the	O
wavelength	O
would	O
be	O
much	O
greater	O
than	O
a	O
bird	O
.	O
</s>
<s>
Another	O
advantage	O
of	O
Fluttar	B-Algorithm
over	O
MCL	O
was	O
that	O
by	O
using	O
multiple	O
Doppler	O
filters	O
in	O
the	O
receiver	O
,	O
the	O
approximate	O
velocity	O
and	O
direction	O
(	O
north	O
or	O
south	O
)	O
could	O
be	O
determined	O
.	O
</s>
<s>
As	O
a	O
consequence	O
,	O
the	O
Fluttar	B-Algorithm
system	O
would	O
have	O
to	O
be	O
much	O
larger	O
and	O
more	O
powerful	O
to	O
provide	O
the	O
same	O
range	O
performance	O
.	O
</s>
<s>
Fluttar	B-Algorithm
was	O
an	O
inexpensive	O
system	O
compared	O
to	O
the	O
main	O
DEW	O
radars	O
.	O
</s>
<s>
The	O
AN/FPS	B-Algorithm
-23	I-Algorithm
stations	O
became	O
active	O
in	O
1957	O
,	O
but	O
soon	O
discovered	O
problems	O
of	O
its	O
own	O
.	O
</s>
<s>
To	O
ensure	O
such	O
fleeting	O
signals	O
were	O
not	O
missed	O
by	O
the	O
operators	O
,	O
the	O
Fluttar	B-Algorithm
system	O
used	O
"	O
alarm	O
gates	O
"	O
that	O
triggered	O
when	O
a	O
signal	O
of	O
a	O
particular	O
type	O
was	O
seen	O
.	O
</s>
