Radar System Engineering

SEC. 13.19] 1’HE RANGB-ll EIGII1’ l.Vl~l CA I’oli 545
the use of mechanical repeaters. Aa extreme case is that of radar relay
(see Chap. 17). Many of these advantages make the technique partitularly
appropriate for use on range-height indicators.
On the other hand, under average conditions, pre-time-base resolution
is considerably less satisfactory than the methods previously described.
The sine potentiometer, though simple, is prone to troublesome irregularities
which cannot be completely filtered, except on extremely slow
scans, without causing phase lags in the basic scanner data. The use of
a carrier and of demodulators introduces considerable complexity compared
with methods described earlier. The necessity of maintaining the
sawtooth generators in proper normalization in order to avoid distortion
is somewhat of a burden compared to other cases where only one such
generator is involved and where, furthermore, any lack of constancy
affects only the size and not the fidelity of the display.
13.19. The Range-height Indicator.—Any off-centered PPI can be
used as a range-height indicator by substituting elevation angle for
azimuth, providing the indicator can follow the scanner involved. In
most cases, it is desirable to present height on a scale that is considerably
expanded in comparison to that used for the display of ground range.
In consequence the most adaptable PPI techniques are those in which
each cartesian coordinate ha? its own amplifier which permits the desired
height expansion to be provided simply by increasing the gain of the
proper channel. Themethods of Figs. 13.46 and 13.51 can both be used
in this way.
Simplification canusually be effected. Thehorizontal sweep always
occurs on the tube face in one direction from the origin. In many cases,
this isalsotrue of the vertical component. (Sometimes negative heights
are involved when the radar is on an elevated site. ) Furthermore, it is
often possible to use one or both of the approximations sin o = o and cos
e = 1. In any case in which a sweep component is unipolar, the clamps
of Fig. 13.46 can be reduced to unstitched d-c restorers, and the switched
clamps of Fig. 13.51 can become single-sided, though still being switched.
The approximation cos 0 = 1 allows the use of unmodulated sweeps in
the horizontal direction; this is of no particular virtue if the resolvedsweep
technique is used, but provides a considerable saving in connection
with the use of a modulated carrier. The approximation sin o = o allows
the use of linear data transmitters, such as linear potentiometers and
condensers.
Since the applications of Fig. 13.46 and Fig. 13.51 to use with an
RHI are fairly obvious, no attempt will be made to discuss them specifically.
Instead, a brief description will be given of an RHI for use with
rapid scans including the “ sawtooth” type developed by certain electrical
scanners (Sees. 9.14, 9.15, and 9.16). It is assumed that sin 0 = d and