Because these special features must be incorporated in a DF system using instantaneous
indicator, its size, weight, power consumption, complexity of design, and maintenance are
greater than for other systems. When not prohibitive, these disadvantages are more than
compensated for by the increased performance obtained when using this type of indicator.
Characteristics of instantaneous indicators in comparison with aural-null are as follows:
(a)
There is greater speed in obtaining bearings because the antenna is
usually not rotated.
(b)
Simplicity of operation is increased. Tuning the receiver and reading the
bearing are the only operations necessary.
(c)
Readability is increased on moderate and weak signals.
(d)
There is equal readability on cw, icw, and mcw signals.
(e)
Readability on swinging signals is increased because the indication
continuously and instantaneously changes with the bearing swing, thus enabling the operator
to choose the most likely bearing.
(f)
Readability on fading bearings is increased because the indicator has a
high degree of discrimination between a change in signal level due to fade, and a change in
bearing and signal indication.
(g)
There is increased readability on combinations of swining, fading and
unfavorably polarized signals, because the indicator exhibits certain features which tell the
operator when conditions are most favorable for obtaining a bearing.
(h)
Sense indication may be simultaneous with the presentation
(continuously sensed) or it may be accomplished by pressing a key (sense switch).
(i)
Readability in the presence of interfering signals is fair, although not as
good as with aural indication.
4. Bearing seeking indicators. Bearing seeking indicators are normally used on aircraft where
an automatic bearing readout is required but size and weight requirements preclude the use
of Instantaneous visual indication. In these systems the antenna system is rotated
automatically to the true bearing position and a pointer on the indicator comes to rest when it
is aligned with the antenna.
IT0302
2-18
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