<s>
A	O
radar	B-Algorithm
display	I-Algorithm
is	O
an	O
electronic	O
device	O
to	O
present	O
radar	B-Application
data	O
to	O
the	O
operator	O
.	O
</s>
<s>
The	O
radar	B-Application
system	I-Application
transmits	O
pulses	O
or	O
continuous	O
waves	O
of	O
electromagnetic	O
radiation	O
,	O
a	O
small	O
portion	O
of	O
which	O
backscatter	B-Algorithm
off	O
targets	O
(	O
intended	O
or	O
otherwise	O
)	O
and	O
return	O
to	O
the	O
radar	B-Application
system	I-Application
.	O
</s>
<s>
Modern	O
systems	O
typically	O
use	O
some	O
sort	O
of	O
raster	B-Algorithm
scan	I-Algorithm
display	I-Algorithm
to	O
produce	O
a	O
map-like	O
image	O
.	O
</s>
<s>
Early	O
in	O
radar	B-Application
development	O
,	O
however	O
,	O
numerous	O
circumstances	O
made	O
such	O
displays	O
difficult	O
to	O
produce	O
.	O
</s>
<s>
Early	O
radar	B-Algorithm
displays	I-Algorithm
used	O
adapted	O
oscilloscopes	O
with	O
various	O
inputs	O
.	O
</s>
<s>
An	O
oscilloscope	O
generally	O
receives	O
three	O
channels	O
of	O
varying	O
(	O
or	O
oscillating	O
)	O
voltage	O
as	O
input	O
and	O
displays	O
this	O
information	O
on	O
a	O
cathode	B-Device
ray	I-Device
tube	I-Device
.	O
</s>
<s>
In	O
a	O
radar	B-Algorithm
display	I-Algorithm
,	O
the	O
output	O
signal	O
from	O
the	O
radar	B-Application
receiver	O
is	O
fed	O
into	O
one	O
of	O
three	O
input	O
channels	O
in	O
the	O
oscilloscope	O
.	O
</s>
<s>
More	O
modern	O
radars	B-Application
typically	O
used	O
a	O
rotating	O
or	O
otherwise	O
moving	O
antenna	O
to	O
cover	O
a	O
greater	O
area	O
of	O
the	O
sky	O
,	O
and	O
in	O
these	O
cases	O
,	O
electronics	O
,	O
slaved	O
to	O
the	O
mechanical	O
motion	O
of	O
the	O
antenna	O
,	O
typically	O
moved	O
the	O
X	O
and	O
Y	O
channels	O
,	O
with	O
the	O
radar	B-Application
signal	O
being	O
fed	O
into	O
the	O
brightness	O
channel	O
.	O
</s>
<s>
The	O
original	O
radar	B-Algorithm
display	I-Algorithm
,	O
the	O
A-scope	O
or	O
A-display	O
,	O
shows	O
only	O
the	O
range	O
,	O
not	O
the	O
direction	O
,	O
to	O
targets	O
.	O
</s>
<s>
A-scopes	O
were	O
used	O
on	O
the	O
earliest	O
radar	B-Application
systems	I-Application
during	O
World	O
War	O
II	O
,	O
notably	O
the	O
seminal	O
Chain	O
Home	O
(	O
CH	O
)	O
system	O
.	O
</s>
<s>
The	O
primary	O
input	O
to	O
the	O
A-scope	O
was	O
the	O
amplified	O
return	O
signal	O
received	O
from	O
the	O
radar	B-Application
,	O
which	O
was	O
sent	O
into	O
the	O
Y-axis	O
of	O
the	O
display	O
.	O
</s>
<s>
The	O
X-axis	O
input	O
was	O
connected	O
to	O
a	O
sawtooth	O
voltage	O
generator	O
known	O
as	O
a	O
time	O
base	O
generator	O
that	O
swept	O
the	O
spot	O
across	O
the	O
display	O
,	O
timed	O
to	O
match	O
the	O
pulse	O
repetition	O
frequency	O
of	O
the	O
radar	B-Application
.	O
</s>
<s>
Using	O
a	O
device	O
known	O
as	O
a	O
radiogoniometer	B-Device
,	O
the	O
operator	O
could	O
determine	O
the	O
bearing	O
of	O
the	O
target	O
,	O
and	O
by	O
combining	O
their	O
range	O
measurement	O
with	O
the	O
bearing	O
,	O
they	O
could	O
determine	O
a	O
target	O
's	O
location	O
in	O
space	O
.	O
</s>
<s>
By	O
selecting	O
a	O
pair	O
of	O
these	O
antennas	O
at	O
different	O
heights	O
and	O
connecting	O
them	O
to	O
the	O
radiogoniometer	B-Device
,	O
they	O
could	O
determine	O
the	O
vertical	O
angle	O
of	O
the	O
target	O
,	O
and	O
thus	O
estimate	O
its	O
altitude	O
.	O
</s>
<s>
Early	O
American	O
,	O
Dutch	O
and	O
German	O
radars	B-Application
used	O
the	O
J-scope	O
,	O
which	O
resembled	O
a	O
circular	O
version	O
of	O
the	O
A-scope	O
.	O
</s>
<s>
To	O
improve	O
the	O
accuracy	O
of	O
angle	O
measurements	O
,	O
the	O
concept	O
of	O
lobe	B-Algorithm
switching	I-Algorithm
became	O
common	O
in	O
early	O
radars	B-Application
.	O
</s>
<s>
A	O
slightly	O
modified	O
version	O
of	O
the	O
K-scope	O
was	O
commonly	O
used	O
for	O
air-to-air	O
and	O
ground-search	O
radars	B-Application
,	O
notably	O
in	O
AI	B-Device
radars	I-Device
and	O
ASV	B-Device
radars	I-Device
-	O
(	O
Air-Surface	O
Vessel	O
)	O
.	O
</s>
<s>
Size	O
of	O
A-scope	O
displays	O
vary	O
,	O
but	O
5	O
to	O
7	O
inch	O
diagonal	O
was	O
often	O
used	O
on	O
a	O
radar	B-Algorithm
display	I-Algorithm
.	O
</s>
<s>
The	O
7JPx	O
series	O
of	O
CRTs	O
(	O
7JP1	O
,	O
7JP4	B-General_Concept
and	O
7JP7	O
)	O
was	O
originally	O
designed	O
as	O
an	O
A-scope	O
display	O
CRT	O
.	O
</s>
<s>
The	O
B-scope	O
'	O
s	O
display	O
represented	O
a	O
horizontal	O
"	O
slice	O
"	O
of	O
the	O
airspace	O
on	O
both	O
sides	O
of	O
the	O
aircraft	O
out	O
to	O
the	O
tracking	O
angles	O
of	O
the	O
radar	B-Application
.	O
</s>
<s>
B-scope	O
displays	O
were	O
common	O
in	O
airborne	O
radars	B-Application
in	O
the	O
1950s	O
and	O
60s	O
,	O
which	O
were	O
mechanically	O
scanned	O
from	O
side	O
to	O
side	O
,	O
and	O
sometimes	O
up	O
and	O
down	O
as	O
well	O
.	O
</s>
<s>
E-scopes	O
are	O
typically	O
used	O
with	O
height	B-Algorithm
finding	I-Algorithm
radars	I-Algorithm
,	O
which	O
are	O
similar	O
to	O
airborne	O
radars	B-Application
but	O
turned	O
to	O
scan	O
vertically	O
instead	O
of	O
horizontally	O
,	O
they	O
are	O
also	O
sometimes	O
referred	O
to	O
as	O
"	O
nodding	O
radars	B-Application
"	O
due	O
to	O
their	O
antenna	O
's	O
motion	O
.	O
</s>
<s>
The	O
elevation	O
information	O
is	O
displayed	O
by	O
drawing	O
a	O
second	O
"	O
blip	O
"	O
offset	O
from	O
the	O
target	O
indicator	O
by	O
a	O
short	O
distance	O
,	O
the	O
slope	O
of	O
the	O
line	O
between	O
the	O
two	O
blips	O
indicates	O
the	O
elevation	O
relative	O
to	O
the	O
radar	B-Application
.	O
</s>
<s>
For	O
instance	O
,	O
if	O
the	O
blip	O
were	O
displaced	O
directly	O
to	O
the	O
right	O
this	O
would	O
indicate	O
that	O
the	O
target	O
is	O
at	O
the	O
same	O
elevation	O
as	O
the	O
radar	B-Application
.	O
</s>
<s>
The	O
"	O
blip	O
"	O
was	O
displayed	O
indicating	O
the	O
direction	O
of	O
the	O
target	O
off	O
the	O
centreline	O
axis	O
of	O
the	O
radar	B-Application
,	O
or	O
more	O
commonly	O
,	O
the	O
aircraft	O
or	O
gun	O
it	O
was	O
attached	O
to	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
however	O
,	O
the	O
range	O
is	O
being	O
measured	O
directly	O
by	O
the	O
radar	B-Application
,	O
and	O
the	O
display	O
was	O
mimicking	O
the	O
optical	O
system	O
to	O
retain	O
commonality	O
between	O
the	O
two	O
systems	O
.	O
</s>
<s>
The	O
PPI	O
display	O
provides	O
a	O
2-D	O
"	O
all	O
round	O
"	O
display	O
of	O
the	O
airspace	O
around	O
a	O
radar	B-Application
site	O
.	O
</s>
<s>
The	O
current	O
position	O
of	O
the	O
radar	B-Application
antenna	O
is	O
typically	O
indicated	O
by	O
a	O
line	O
extending	O
from	O
the	O
center	O
to	O
the	O
outside	O
of	O
the	O
display	O
,	O
which	O
rotates	O
along	O
with	O
the	O
antenna	O
in	O
realtime	O
.	O
</s>
<s>
The	O
PPI	O
display	O
is	O
typically	O
what	O
people	O
think	O
of	O
as	O
a	O
radar	B-Algorithm
display	I-Algorithm
in	O
general	O
,	O
and	O
was	O
widely	O
used	O
in	O
air	B-Application
traffic	I-Application
control	I-Application
until	O
the	O
introduction	O
of	O
raster	O
displays	O
in	O
the	O
1990s	O
.	O
</s>
<s>
PPI	O
displays	O
are	O
actually	O
quite	O
similar	O
to	O
A-scopes	O
in	O
operation	O
,	O
and	O
appeared	O
fairly	O
quickly	O
after	O
the	O
introduction	O
of	O
radar	B-Application
.	O
</s>
<s>
As	O
with	O
most	O
2D	O
radar	B-Algorithm
displays	I-Algorithm
,	O
the	O
output	O
of	O
the	O
radio	O
receiver	O
was	O
attached	O
to	O
the	O
intensity	O
channel	O
to	O
produce	O
a	O
bright	O
dot	O
indicating	O
returns	O
.	O
</s>
<s>
The	O
specialist	O
Beta	O
Scan	O
Scope	O
was	O
used	O
for	O
precision	B-Algorithm
approach	I-Algorithm
radar	I-Algorithm
systems	O
.	O
</s>
