Navigation Antenna, Receiving Signals #
To navigate to its destination and communicate with air traffic control and/or other aircraft, an airplane uses a variety of radio frequencies. To do this, the onboard radio equipment employs a variety of antenna types like a Navigation Antenna for instance, each intended for a specific frequency range.
Each of these antennas has its own frequency and application characteristics, as well as its own position aboard the aircraft. Even the link between the antenna and the avionics is governed by its own set of rules.
Some may question if the aircraft antennae can be painted. That depends on the type of paint used, as well as the antenna’s frequency and bandwidth; consult the antenna’s manufacturer or simply don’t paint them.
The frequency ranges used in aircraft navigation with are larger than those used in voice communications. In the UHF frequency ranges, LORAN-C in the LF range and LORAN-A in the MF band, VOR ILS Glide path, and GPS are used. They can both be used simultaneously. The rationale for employing all of these frequency bands evolved over time.
In aviation, LORAN-C in the LF band isn’t as prevalent as it formerly was, although it can be more dependable because the transmitters have far higher power than spaced-based GPS. 90 – 110 kHz is the frequency range employed. The application is now mostly used in the maritime industry as it is being phased out.
ADF – NDB #
Because these systems utilize low-frequency signals (LF band: 30 – 300 kHz), their antennas are much larger than a VHF communications antenna. The antenna system comprises of a long wire and tail, as well as a loop-shaped sensing antenna. The signals are then electronically merged, allowing the receiver to find and indicate the NDB station’s direction.
VOR – ILS #
VOR radio stations operate between 112 and 118 MHz on the VHF band (ILS localizers operate between 108 and 112 MHz). Glide slope frequencies are three times those of the VOR and can be found around 328-335 MHz UHF). Because the transmissions are horizontally polarized, you’ll require a horizontally mounted antenna. Many aircraft have the dipole mounted on the vertical fin, although there have also been aircraft with the antenna mounted on the bottom of the tail.
Because this antenna bends backwards and forwards, it is sensitive in all directions (omni). Another benefit is that by bending the radiators, it may be used with coax wire with a 50 ohm impedance. A standard open dipole has a 73 ohm impedence and should not be used with a 50 ohm cable or radio. Performance suffers as a result of the mismatch. A Balun (transformer) was previously mentioned as a solution to this problem.
Tactical Air Navigation Air & VOR (TACAN – VORTAC) #
TACAN is a UHF radio navigation system used by the military to provide combined azimuth and distance information. This TACAN system’s DME component is accessible for civil usage. VOR and TACAN are co-located at some military airports, and these facilities are known as VORTACc (short for VOR and TACAN).
The ILS landing system includes marker beacons. They use the frequency 75 MHz and have receivers built into the intercom system (Garmin, Bendix King and others). The antenna is usually a boat-style device that is mounted in the middle of the fuselage under the plane. The transmitters are spaced at predefined intervals along the runway’s centerline.
GPS / Navstar #
These frequencies are commonly found between 1176 and 1379 MHz in the UHF spectrum. In around 1.5 hours, the signal is delivered by at least 24 low-altitude satellites orbiting the Earth (there are more for backup purposes). This signal is circularly polarized, and the antenna must be mounted on top of the airplane in order for it to ‘see’ the sky. Weather or ionospheric impacts produced by solar flares or day/night variations have little effect on reception.
A GPS antenna is ‘active,’ which means it has an amplifier built in next to it to boost satellite signals and compensate for cable losses. Any excellent UHF cable, such as the LMR-400, would suffice. Because the amplifier is fed by this connection, it must not be shorted. This antenna is mounted on the aircraft’s roof to allow it to ‘see’ GPS satellites.