3-11
Figure 3-10.—Deflection coil currents.
CRT Screen Persistence
A ppi requires a crt in which the screen is coated with a long-persistence phosphor. This is necessary
because each target reflects energy for only a short period of time during each rotation of the antenna.
Therefore, the target indication on the face of the crt must be able to continue to glow during the portion
of antenna rotation when the target is not reflecting energy.
Q4. What coordinates are presented on a ppi scope?
Q5. What type of deflection is preferred for a crt electron beam?
Q6. Which of the two types of deflection coils (fixed or rotating) is used most often?
RANGING CIRCUITS
The accuracy of target-range data provided by a radar varies with the use of the radar. For example, a
weapons systems radar operating in a search mode is required to be accurate within a small percentage of
its maximum range. However, an intercept radar, operating in a tracking mode, must supply range data
that is even more accurate; it must be within a few yards of the actual range.
In some applications of radar, the indicator sweep is calibrated by a transparent overlay with an
engraved range scale. This overlay enables the operator to estimate the range of targets. In other
applications, electronic range marks are supplied to the indicator. They usually appear as vertical pulses
