<s>
WSR-74	B-Algorithm
radars	B-Application
were	O
Weather	B-Application
Surveillance	I-Application
Radars	I-Application
designed	O
in	O
1974	O
for	O
the	O
National	O
Weather	O
Service	O
.	O
</s>
<s>
There	O
are	O
two	O
types	O
in	O
the	O
WSR-74	B-Algorithm
series	O
,	O
which	O
are	O
almost	O
identical	O
except	O
for	O
operating	O
frequency	O
.	O
</s>
<s>
The	O
WSR-74C	O
(	O
used	O
for	O
local	O
warnings	O
)	O
operates	O
in	O
the	O
C	B-Algorithm
band	I-Algorithm
,	O
and	O
the	O
WSR-74S	B-Algorithm
(	O
used	O
in	O
the	O
national	O
network	O
)	O
operates	O
in	O
the	B-Algorithm
S	I-Algorithm
band	I-Algorithm
(	O
like	O
the	O
WSR-57	O
and	O
the	O
current	O
WSR-88D	B-Algorithm
)	O
.	O
</s>
<s>
S	B-Algorithm
band	I-Algorithm
frequencies	O
are	O
better	O
suited	O
because	O
they	O
are	O
not	O
attenuated	O
significantly	O
in	O
heavy	O
rain	O
while	O
the	O
C	B-Algorithm
Band	I-Algorithm
is	O
strongly	O
attenuated	O
,	O
and	O
has	O
a	O
generally	O
shorter	O
maximum	O
effective	O
range	O
.	O
</s>
<s>
The	O
WSR-57	O
network	O
was	O
very	O
spread	O
out	O
,	O
with	O
66	O
radars	B-Application
to	O
cover	O
the	O
entire	O
country	O
.	O
</s>
<s>
There	O
was	O
little	O
to	O
no	O
overlap	O
in	O
case	O
one	O
of	O
these	O
vacuum-tube	O
radars	B-Application
went	O
down	O
for	O
maintenance	O
.	O
</s>
<s>
The	O
WSR-74	B-Algorithm
was	O
introduced	O
as	O
a	O
"	O
gap	O
filler	O
"	O
,	O
as	O
well	O
as	O
an	O
updated	O
radar	B-Application
that	O
,	O
among	O
other	O
things	O
,	O
was	O
transistor-based	O
.	O
</s>
<s>
In	O
the	O
early	O
1970s	O
,	O
Enterprise	O
Electronics	O
Corporation	O
(	O
EEC	O
)	O
,	O
based	O
out	O
of	O
Enterprise	O
,	O
Alabama	O
won	O
the	O
contract	O
to	O
design	O
,	O
manufacture	O
,	O
test	O
,	O
and	O
deliver	O
the	O
entire	O
WSR-74	B-Algorithm
radar	B-Application
network	O
(	O
both	O
C	O
and	O
S-Band	B-Algorithm
versions	O
)	O
.	O
</s>
<s>
WSR-74C	O
radars	B-Application
were	O
generally	O
local-use	O
radars	B-Application
that	O
did	O
n't	O
operate	O
unless	O
severe	O
weather	O
was	O
expected	O
,	O
while	O
WSR-74S	B-Algorithm
radars	B-Application
were	O
generally	O
used	O
to	O
replace	O
WSR-57	O
radars	B-Application
in	O
the	O
national	O
weather	O
surveillance	O
network	O
.	O
</s>
<s>
When	O
a	O
network	O
radar	B-Application
went	O
down	O
,	O
a	O
nearby	O
local	O
radar	B-Application
might	O
have	O
to	O
supply	O
updates	O
like	O
a	O
network	O
radar	B-Application
.	O
</s>
<s>
128	O
of	O
the	O
WSR-57	O
and	O
WSR-74	B-Algorithm
model	O
radars	B-Application
were	O
spread	O
across	O
the	O
country	O
as	O
the	O
National	O
Weather	O
Service	O
's	O
radar	B-Application
network	O
until	O
the	O
1990s	O
.	O
</s>
<s>
They	O
were	O
gradually	O
replaced	O
by	O
the	O
WSR-88D	B-Algorithm
model	O
(	O
Weather	B-Application
Surveillance	I-Application
Radar	I-Application
-	O
1988	O
,	O
Doppler	O
)	O
,	O
constituting	O
the	O
NEXRAD	B-Algorithm
network	O
.	O
</s>
<s>
The	O
WSR-74	B-Algorithm
had	O
served	O
the	O
NWS	O
for	O
two	O
decades	O
.	O
</s>
<s>
No	O
WSR-74S	B-Algorithm
'	O
s	O
are	O
in	O
the	O
NWS	O
inventory	O
today	O
,	O
having	O
been	O
replaced	O
by	O
the	O
WSR-88D	B-Algorithm
,	O
but	O
some	O
of	O
these	O
radars	B-Application
are	O
in	O
commercial	O
use	O
.	O
</s>
<s>
WSR-74	B-Algorithm
sites	O
include	O
the	O
following	O
two	O
categories	O
:	O
</s>
<s>
WSR-74S	B-Algorithm
providing	O
local	O
coverage	O
.	O
</s>
