Figure 2-4.—Transponder output pulse train.
15-HZ-BEARING INFORMATION
The rf energy from the TACAN transmitter is fed
to the antenna central element, which has no
The timing of the transmitted pulses supplies the
directivity in the horizontal plane. Parasitic elements
actual distance information to the aircraft. This leaves
positioned
around the central element
are
amplitude modulation as another medium for the
electronically rotated (switched on and off) at 15
transponder to convey other information to the
revolutions per minute. (See the section below on the
aircraft. The TACAN beacon-transponder modulates
OE-273(V)/URN antenna group). The distance
the strength of the pulse to convey bearing information
between the central element and the parasitic elements
by producing a specific directional-radiating pattern
is selected to obtain a cardioid radiation pattern. To
rotated around a vertical axis. This signal, when
an aircraft at a specific location, the distance data
properly referenced, indicates the aircraft’s direction
pulses appear to contain a 15-Hz amplitude-modulated
from the TACAN facility. This signal and distance
signal because of the rotation of the cardioid radiation
data give a two-piece fix (distance and direction) for
pattern. This pattern is shown
determining specific aircraft location.
and view B.
in figure 2-5, view A
2-3
