2.4 Antenna Installation
2.4.1 Antenna Location And Mounting
The AT 150 Antenna supplied in the Installation Kit should be mounted on the bottom surface of the aircraft and located such that it will be in a vertical position when the aircraft is in level flight. The area surrounding the antenna location should be free of protrusions which could interfere with the line-of-sight characteristics of a VHF signal. The following rules should be observed with regard to the ground plane.
- Metallic Mounting Surface
Mount the antenna in the center of a 6" (152.4 mm), minimum radius, ground plane. Antenna located near the edge of a ground plane may cause holes in the radiation and reception patterns. - Non-Metallic Mounting Surface
Aircraft with fabric, wood, or fiberglass fuselage covering must have a metal ground plane with a 6" (152.4 mm) minimum radius. This could be as simple as aluminum foil cemented inside wood or stiff fiberglass skin, or a doubler plate on a fabric covered aircraft. Such a ground plane should be either well bonded to the airframe, or well insulated from it, to prevent noise problems or erratic operation. Antenna mounting hardware must electrically connect the ground plane to the antenna.
A doubler plate will be needed for an airworthy installation on most aircraft. Check the airworthiness regulations of the country of aircraft registry for acceptable mounting methods.
Figure 2-3 illustrates the antenna mounted and the necessary minimum clearances. Remove all oxidation, paint, or other finish to permit good electrical contact between the antenna base and the aircraft. Electrical ground will be carried by the mounting hardware. Do not paint. The antenna should not be painted or coated with any other finish.
Figure 2-3 - AT 150 Antenna Mounting
2.4.2 Antenna Extension Cable
The Installation Kit provides two UG-88U BNC connectors for fabrication of the antenna extension cable. The total length of this cable should not exceed 9 feet (2.7m). Should a cable of greater length be required, a coaxial cable type should be selected whose attenuation does not exceed 2 dB over the entire length.
Narco makes available eight and nine foot low loss extension cables, complete with factory-installed BNC connectors; order Part Number 90624-0096 (8 foot) or Part Number 90624-0108 (9 foot).