TM
11-5985-284-15
direction, they add together and provide a marked
of resistors R1 through R9 on subassembly A3.
increase in output signal to point the way to the
The amount of attenuation is selected by AT-
TENUATOR switch A3S1 in four steps. Each
aimed away from the transmitting station. The
of the first three steps provides approximately 10
dotted arrow is the same current, while the arrow
composed of triangles is the loop output current
(as shown in D, fig. 4-2) with the loop away from
() position of switch A3S1 couples a tap of L1
the station. Since these current components op-
directly to RF output connector J1. This antenna
pose each other, very little output is obtained, prov-
ing this is not the true direction to the station. By
ohms.
similarly summing up the circular sense pattern
and the figure 8 loop pattern in all directions, the
simple loop passes two identical nulls and two
cardiod pattern is obtained.
identical maximum points, 180 apart. The pat-
g. While the sensing definitely points the direc-
term leaves 180 uncertainty as to the direction of
tion to the transmitter, the broadness of the lobe
makes it difficult to spot the bearing sharply
(maximum pjoints or nulls) is used to find the di-
enough. Using the null to sharpen the bearing and
front of or behind the loop, another element is used
following the null to the station (para 2-7e) are
standard direction finding practices. If the
to eliminate one direction. The sense of the bear-
operator loses his bearings and has difficulty in re-
ing can be determined by introducing a small volt-
locating the general direction of the transmitter,
age derived upon raising the vertical sense whip
the sense operation should be repeated.
antenna. This sense whip antenna is a simple
h. The sensing current must be equal to, or
vertical whip antenna, 12 inches long, whose output
slightly less than, the net loop current. If the
is mixed with that of the loop. The sense whip
sense current is too small, a pattern consisting of
antenna current, caused by electric field activity,
one large lobe, one small lobe, and two nulls less
combines with the loop circuit current in trans-
than 180 apart is produced. If the sense current
former L1. The vector addition of these currents
is too high, it will mask the loop characteristics
produces the desired cardiod response (pattern D,
and produce a pattern with an indistinct maximum
and minimum.
f. Superimposing the circular sense pattern over
i. For
proper operation of
Antenna AT-1082/
the loop pattern (since they occur at the same in-
PRC, the signal output (applied to the ]imiter of
stant) provides the loop plus sense cardiod pattern
a receiver) should be of such an amp] itude as to
appear on the slope of the limiter curve. To ac-
the loop aimed at the transmitting station. The
complish this, the step attenuator circuitry of AT-
dotted arrow represents the current in any direc-
1082/PRC, which consists of a ladder-type pi-net-
tion, while the arrow composed of triangles repre-
work of resistors, may be used as required (d
sents the current flow within the loop (as shown in
above). Tile amount of attenuation depends
C, fig. 4-2) with the loop aimed at the station.
upon the position of the ATTENUATOR switch
Since both of these currents circulate in the same
4-6
Change 1