Antennas - Nat SM41 Installation And Operation Manual

SM41 Rev. 4.00 NPX138 Panel Mount Radio Manual
minimum at the antenna. Avoid sharp bends in the coax cables (minimum 3" radius) to
prevent severe reflections. If sharp bends are required, use 90° elbow adapters.
Fabrication & installation of wiring harness should be in accordance with AC 43.13-1A
chapter 11, sections 3 and 7.
Grounding and bonding should be in accordance with AC 43.13-1A chapter 11, section 3.
2.3.5

Antennas

Correct antenna placement and mounting is critical in order to achieve the best possible
performance. In general, keep all antennas as widely separated as possible and clear
of any large airframe obstructions.
Installation of the antenna should be in accordance with AC 43.13-1A chapter 2, section
3, chapters 5 & 6, and AC 43.13-2A chapter 3. If possible, the antenna should be
located a minimum of 12 ft from aircraft navigation receiver antennas and a minimum of
4 feet from aircraft communications and ELT antennas. Be careful not to choose
separations that closely approximate ¼, ½ or whole-number multiples of the navigation
or communications system wavelength.
Note: Avoid any placement that puts antennas of like frequencies close together.
Bottom mounted antennas will perform best in flight, but poorest on the ground during
testing. Antennas may be severely degraded by 'masking' effects of the fuselage or
stabilizers, and generally give best performance when bottom mounted.
To reduce interference from rotor modulation and other undesirable stimuli, any blade or
whip antenna must be surrounded by a ground plane surface (metallic, grounded
material) with a radius equal to or greater than the height of the antenna. Under the
same conditions, the antenna is also much less likely to cause interference to other
aircraft systems (e.g. coupling into audio system, fluctuations in instrumentation, etc.).
Poor grounding will result in severe reflected power and high levels of RFI throughout
the airframe.
Avoid antenna locations that will become fouled with oil, water, fuel or dirt, as this will
degrade performance. Roof mounts (in close proximity to rotor blades) are permissible.
Nov 10, 2003 Page 2-3
ENG-FORM: 805-0104.DOT
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