Radar System Engineering

220
THE EMPLOYMENT OF RADAR DATA [SEC.7.3
Further, the screen must be well shielded from stray light if this
method is to be used, and this somewhat limits its usefulness.
2. Televising the persistent screen and using the video signals so
obtained to modulate a high-intensity short-persistence tube suitable
for projection. The results obtained with thk rather complicated
scheme up to the end of the war were mediocre.
3. Storing the radar picture on an image orthicon or other storage
device which can be rapidly scanned electrically to produce television
signals. This method, although not well developed at the
end of the war, holds great future promise.
4. Use of a dark-trace tube, or “ skiatron. ”
5. Rapid photographic projection.
The last two methods mentioned are the only ones developed fully
enough during the war to warrant further description.
Spherical mirror
.-+
Imageplane
I
1A
arc lamp ,“1~
Field lens
FIG-.7.6.—Schmidt projection system for skiatron.
The Skiatron.—The dark-trace tube, described briefly in Sec. 13”2,
has been used as the basis for a reasonably successful projection system
both in England and in America, the principal differences being in the
optical systems used. In England, an extremely flat-faced tube serves
as the source for a wide-aperture lens system; in this country a tube has
been designed to fit a Schmidt optical system.
Figure 7.6 illustrates the latter. The cathode-ray tube, whose face
is precisely spherical, is mounted with this face concentric with the
spherical mirror of the optical system. Light from an intense mercuryarc
or tungsten source is concentrated on the tube face by the lens-andmirror
arrangement shown. The geometry is so chosen that the Schmidt
correcting plate comes roughly at the neck of the cathode-ray tube. A
45° mirror reflects the light to a horizontal projection screen which forms
part of the top of the cabinet housing the equipment.