Radar System Engineering

SEC. 78] TELERAN 241
weather and route information, can provide all of the data needed by
aircraft for en-route navigation and for airport approach. Further, highprecision
ground radar can supply all the information that a pilot requires,
in addition to his own flight instruments, for instrument approach and
landing. All that is required is to get this information into the aircraft,
where it can be displayed to and used by the pilot.
It is proposed to add to the display of a ground radar a chart that
contains map, airways, and weather information of interest to pilots, and
to send the resulting picture by television to the aircraft, where it is displayed
to the pilot. Televising of the display is preferred to the use of
the radar-relay methods described in Chap. 17 because television does
not require the use of persistent phosphors, with their low maximum
level of light intensity, in the aircraft cockpit, where the level of ambient
light is likely to be high.
On the basis of the assumption that display of all aircraft in the picture
offered a pilot would be useless and confusing, it is proposed to
separate the radar signals according to the altitude at which the corresponding
aircraft are flying. Thus, for example, a pilot at 5000 ft would
be sent signals sho~}-ing the positions of all aircraft in his neighborhood
and in the altitude range from 3500 to 6000 ft. This can be accomplished
technically by supplying each plane with a transponder beacon ~~rhose
reply signal is coded (Sec. 8.8) in accordance with the altitude at which
the plane is flying. This coding can be controlled automa~ically by an
altimeter. At the ground radar station, signals in the various altitude
intervals can be sorted out and displayed separately for transmission to
aircraft using the system. The transponder also increases the range of
the radar equipment and, if a reply frequency different from the transmitter
frequency of the radar is used, eliminates difficulty from ground
echoes which might interfere with seeing low-flying aircraft.
Figure 7.18 ~holl-s a Teleran display as it might appear to a pilot
flying at 11,000 ft. .kt this altitude, since topographical features are of
little interest, nothing is shown except other aircraft, towns, airports,
airways, frequency channels in use by Teleran ground stations, and the
direction and velocity of the wind. To assist the pilot in flying a course,
the compass reading is repeated on a disk mounted over the face of the
indicator and ruled with parallel lines showing the heading of the aircraft.
These lines are shown dashed in Fig. 718.
It is essential for the pilot to know which of the beacon responses is
that of his own plane. This is accomplished by having a rotating radial
line, centered at the radar station (which appears in the center of the
picture), form part of the display information transmitted from the
ground station, This line is normally invisible, but the television receiver
is controlled by a signal from the transponder in such a way that the line