Radar System Engineering

174 THE GATHERING AND PRESENTATION OF RADAR DATA [SEC. 67
face (Fig. 6.1 1). It can be used in conjunction with a PPI or a type B
display as an aid to homing (Sec. 6.13). This display has the great disadvantage
that its signal-to-noise discrimination is very poor if signals
are displayed for an appreciable fraction of the pulse cycle (see Chap. 2).
For this reason, the C-scope is usually blanked except for a short range
interval including the signal of interest. Initial recognition of the target
signal is accomplished on the other display, and the proper range setting
for the C-scope display interval is determined either by inspection or by
displaying on the search tube an electronic marker derived from the
C-scope brightening signal.
The V-beam height indicator is an example of the type of display considered
in this section, but its description is deferred to Sec. 6.12.
6“7. Three-dimensional Display s.—In spite of the fact that the face
of the cathode-ray is two-dimensional, two conventionalized three-
B
--
4
%. E3
.- c -- C
22
A-
~1
@ -30° 0 +30”
—
position of
antenna beam
(a) Double-dot indicator. (b) Pattern of spiral scan (.) Radial time base (RTBJ
used with displays indicator.
shownat (a) and (c).
FIc. 6.12.—Three-dimensionaldisplays. A, B, and C are targets,
dimensional displays [as distinguished from error indicators (Sec. 68)]
have been successfully used in situations involving relatively few targets.
The “Double-dot” Display.—~ modified type B presentation on which
elevation angle is roughly indicaied is known as the “double-dot” display.
On alternate range sweeps the origin of the pattern is moved to the right
and left respectively by a fixed amount (Fig. 6. lti). On the sweeps
corresponding to the right-hand position the origin is simultaneously
shifted vertically by an amount proportional to the sine of the elevation
angle. Any single echo therefore appears in two neighboring positions,
and the slope of the line joining the two “ dots” is a rough measure of
elevation angle which is accurate to two or three degrees under the usual
circumstances of use. This display has been used in air-to-air homing
(AX/APS-6).
The “Radial Time Base” Indicator.-The radial-time-base indicator
is a three-dimensional display which, like the double-dot display, is beat