Figure 2-1. Airborne radio direction finding.
PART A: COMPONENTS
Regardless of the requirement, direction finding equipment will have the same basic
components. (See Figure 2-2).
a directional antenna
a radio receiver
a coupling system
a method of indication
Suppose we refer to the portable radio mentioned in the first lesson. The directional antenna
is the bar antenna. The receiver is the radio itself. The coupling system is the "direct
coupling." The indication system is the "aural null." Each is designed for the specific job it is
supposed to do, and is the most efficient piece of equipment the manufacturer can use within
he parameters (requirements) needed. Probably the first consideration for the manufacturer
was cost efficiency, second was size and weight. Third was ease of use. Fourth was
neatness of design. There are others but our discussion will stop here.
The Directional Antenna. The bar antenna is the most compact for the frequency range of the
receiver. It is highly efficient and relatively inexpensive, consisting of a number of turns of
wire wound around a core. The fact that it is bidirectional was of secondary importance to
the manufacturer, but it makes a net illustration for the DF student. Of course, the user of the
radio is more interested in the peak reception than the null, but still the directivity is there and
can be used. As an illustration of the case of use of the null, as compared to the maximum
point, try lining yourself with the length of the antenna as compared with centering yourself on
the width.
IT0302
2-2
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