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Session 4: Flight Inspection Technology (including ADS-B and RFI)

Ground Check of GNSS Antennas on Aircraft
Rolf Seide, Aerodata AG, Germany
Location: Regency Ballroom
Date/Time: Tuesday, Apr. 17, 9:30 a.m.

After installation of new Flight Inspection antennas on aircraft they should be tested on ground in the hangar according to their typical technical data.
Typically with normal RX/TX antennas the steps are:
• Bonding
• Cable loss
• VSWR (reflected energy versus frequency with reference to the nominal impedance)
• Frequency depending signal response
On active antennas like GNSS/GPS/GLONASS/Terrastar or ADF the VSWR check is not possible, because an active component like an internal amplifier (made for signal flow in one direction only) will not respond to reflection measurements (signal flow in two directions).
This paper shows practical solutions to validate GNSS antenna data after installation and a handy way to check antenna performance as a maintenance task. Without these test procedures trouble shooting on GNSS antennas and wiring is only possible by changing devices and the hope, that the failure disappears.
With the test installation described, further measurements on aircraft GNSS antennas can be performed to identify overload situations due to strong in-band and out-of-band transmission from the own aircraft or high power ground stations (e.g. RADAR, UMTS/LTE) resulting in loss of GNSS signals.
Additionally, a faulty (interference) situation found on an airborne multiple-antenna installation found in practice, resulting in temporary loss of GNSS in flight, is shown.



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