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RELEASED FOR THE EXCLUSIVE USE BY: AIRCRAFT ELECTRONICS ASSOCIATION
B
2.4.3.B.4
ANTENNAS MAY BE MOUNTED IN LINE OR SIDE-BY-SIDE, the former be-
ing the best choice of the two. When using side-by-side installations, the an-
tennas should be mounted on a flat surface of the aircraft. The angle between
the antenna centerlines should be less than 6 deg. Failure to do so will result
in erratic operation on the ground, i.e., the needle will fluctuate as much as 20
feet, dependent upon the angle between centerlines. Airborne operation will
be satisfactory.
2.4.3.B.5
DUAL INSTALLATION: Two (2) receive and two (2) transmit antennas are re-
quired for a dual installation, one pair for each system. The transmit antenna
of one system must be located as far as possible from the receive antenna of
the other system in order to avoid interference between the two systems (see
Figure
2-3).
2.4.3.B.6
ANTENNAS SHOULD BE MOUNTED NO LESS THAN 20 INCHES APART
(measure from center to center) in order that leakage between the antennas
remains at a tolerable level. The pointer may not stow above 2500 feet if the
leakage between the antennas is too great.
2.4.3.B.7
ANTENNAS SHOULD NOT BE SEPARATED BY A DISTANCE GREATER
THAN THE ANTENNA HEIGHT ABOVE THE TERRAIN AT TOUCHDOWN.
If the antennas are separated by more than this distance, sufficient terrain
ares is not illuminated for ground level operation. The antennas should be
mounted closer than the antenna height above the terrain (but no less than 20
inches) if the angle between the antennas is greater than 6 deg.
2.4.3.B.8
ANTENNA LOCATIONS SHOULD PROVIDE 120 DEGREE CLEARANCE
CONES - no aircraft projection or other antenna should lie within these cones.
A fixed object in the cone could cause the altimeter to lock on to a single alti-
tude while a moving projection (gear, flaps, etc.) could cause erratic operation.
2.4.3.B.9
SURFACE AREA BETWEEN ANTENNAS SHOULD BE FREE FROM
SEAMS OR OTHER DISCONTINUITIES. Never mount an antenna directly
on a seam. If antennas must be separated by a seam, make sure the two
pieces of aircraft skin are electrically bonded together by adding bonding
straps (i.e., have multiple straps across seam separating the two antennas).
Follow rule C.1 when bonding the straps. Failure to bond properly can cause
loss in system sensitivity and/or cause the pointer to momentarily come into
view above 2500 feet AGL (this phenomena is commonly called "peaking").
2.4.3.B.10 ANTENNA MUST NOT BE LOCATED IN AREAS WHERE EXCESS WATER
CAN ACCUMULATE. Water between the antenna flange and aircraft skin will
cause loss of system sensitivity and peaking.
2.4.3.B.11 CONNECTORS ON ANTENNAS SHOULD BE MOUNTED PERPENDICU-
LAR TO A LINE DRAWN THROUGH THE TWO ANTENNAS. The antennas
are so designed that minimum coupling occurs when mounted as above. Any
other mounting may cause the altimeter to lock on to erroneous altitudes when
flying above 2500 feet AGL.
2.4.3.C
Implementing the Antenna Installation
2.4.3.C.1 ANTENNA AND AIRFRAME SURFACES MUST BE FREE OF PAINT OR
OTHER INSULATING MATERIALS, INCLUDING CHROMATE. Apply Alumi-
Rev 6, June 2003
IM 006-00104-0006.dwd
KRA 405
Page 2-5
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