TM 11-5826-225-35
Section Il. DETAILED FUNCTIONING OF RADIO RECEIVER R1391/ARN-83
fixed loop antennas mounted at right angles to
1-4. General
each other with loop 2 sensitive to radio signals
Radio Receiver R1391/ARN83, is the main
along the aircraft longitudinal axis and loop 1
operational unit of Direction Finder Set (AN/
sensitive to radio signals along the aircraft lat-
ARN-83. The receiver is a single-conversion
eral axis. Each loop antenna is terminated in a
superheterodyne low frequency receiver, tun-
stator winding of resolver B3. The rotor (L3)
able from 190 kc to 1750 kc in three ranges. In
of B3 is mechanically coupled to a servo mech-
automatic direction finding ( adf ) mode, it proc-
anism capable of rotating it through 360 de
esses RF input signals from a directional loop
grees with its coupling to L1 and L2 varied ac-
antenna (fixed ) and a nondirectional sense an-
cordingly. The combination of Ll, and, and L3,
tenna to determine the hearing of radio sta-
is called goniometer. Assume that loop 1 is
tions. The loop antenna RF output is impressed
along a line directly north and south, and loop
on the stator windings of a resolver ( goniom-
2 is along the east-west line. If a radio station
eter) driven by a closed loop servo mechanism.
RF source is north of loop 2, maximum signal
A phase comparison between RF signals, from
will be induced in loop 2 and minimum signal in
the resolver rotor winding and the sense an-
loop 1 (fig. 12). A current will flow in winding
tenna signals, determines whether the resolver
L2 of resolver B3 and none will flow in L1. If
rotor electrical zero or null position is either to
the rotor (L3) of B3 is rotated so that max-
the right or left of the direction of radio sta-
imum coupling to L1 occurs, no signal will be
tion signals. After this is determined, the servo
induced in L3 and if a pointer was attached to
mechanism rotates the resolver in the direction
the rotor of B3 (assuming proper orientation),
required to reach a null, which is the direction
one end of the pointer would indicate O degrees
of the radio station. A synchro transmitter,
(north) on a 360-degree dial and the other end,
geared to the resolver, transfers bearing data to
would point 180 degrees or south. If the direc-
the aircraft bearing indicator. The Mock dia-
tion of a radio station is at a bearing of 135
gram illustrated in figure 5-2, shows the rela-
degrees (fig. 12), the bearing is not perpendic-
tionship of all functional circuits in the receiv-
ular to the plane of either loop 1 or loop 2. This
er. The following paragraphs contain detailed
will induce a signal voltage in each loop with a
circuit functions in the same order as the direc-
phase difference of 180 degrees and equal signal
tion of signal flow depicted in figure 5-2. A
amplitudes. Maximum signal will be induced in
complete Schematic of the receiver is shown in
the rotor winding of B3 when it is coupled to
either L1 or L2 and minimum signal output will
1-5. Receiver Loop Antenna and
result when the rotor apparent null is posi-
Goniorneter Circuit Functioning
tioned for minimum coupling to both L1 and
L2. The resolver functions as a miniature rotat-
a. Antenna AS-1863/ARN-83, comprises two
ing figure-eight loop antenna pattern and the
Change 5 1-5
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