Radar System Engineering

SEC. 13.3] SELECTION OF THE CATHODE-RAY TUBE 485
because of the greater power required for deflection. These
diiTerences are of significance only in airbmne equipment.
4. The grid-modulation characteristic of most electrostatic tubes
follows approximately a square law, whereas that of the guns used
in most magnetic tubes is cubic. As compared with a linear
response, these characteristics have the unfortunate property of
lowering the dynamic range of usable echo intensities since they
reduce the ratio between the upper limit of useful signal swing,
set by the tendency to defocus, and the level below which the
intensity is insufficient.
TAZLE 13.1.—CATH0DE-RA%TUBES COMMONLYUSEDiFOR RADAR APPLICATIONS
Bulb
number
Jseful
liameter,
in.
Type of
deflection
hfax. accelerating
voltige
(nominal) Specified
maximum
POSL spot diam-
Ieflec- eter, mm*
Anode
tion
mode
Commonly
used ecreens
2A
2B (New)
3B
3D (Central
electrode)
3F
3J
3H
4.4
5B
5C
5F
5L
7B
9G
12G
12D
1.7!
1.7:
2.7!
2.7!
131ectroetatic
Electrostatic!
Electrostatic
Electrostatic
2.7! Electrostatic
2.7{ Electrostatic
2.5 }Iagnetic
3.3: Magnetic
4.5 Electrostatic
4.5 Electrostatic
4.2E Magnetic
4.5 Electrostatic
6.0 Nlagnetic
7.62 Magnetic
10.0 Electrostatic
10.0 Magnetic
1000
2500
2000
2000
2000
2000
5000
9000
2000
2000
7000
2000
7000
7000
4000
7000
0.5to 0.6
. ., ..,,.
o.55t00.7!
0.6tol. O
4000 . . . . . . . . . .
4000 o.75too.9
0.5to 0.6
. . . . 0.3
. . . . 0.6tol. O
4000 0.6to 0.9
0.5to 0.6
4& . . . . . . . .
o.75t00. s!
.,. l,ot01,2
6000 1.2tol.8
.,. 1.35 t01,5
P-1
P-1
P-1
P-1
P-7
P-1, P-7
P-7, P-12, P-14
P-lo
P-1
P.1, P-7, P-12, P- 4
P-7, P-12, 1’-14
P-1, P-7
P-7, 1’-12, P-14
P-7, P-12, P-14
P-1, P-7
P-7
● Mont magnetic tubes actually give fmm 0.5 to 0,7 of this maximum spot size. Electrostatic tubm
are in general near the maximum.
As a result of these factors, electrostatic tubes are invariably used for
deflection-modulated indicators, but, except in cases of extreme weight
limitation, magnetic tubes are used for most intensity-modulated displays.
The size of the tube selected depends upon the particular application.
The relative resolution is fairly independent of the size, so that from this
standpoint alone there is little value in increasing the screen diameter