Interference Testing of the 1st Adjacent-channel of the Ground-Based Augmentation System (GBAS) and the Very High Frequency (VHF) Omni-Directional Radio Ranges (VOR)

Ernest Etienne, Victor Hinton, Leonixa Salcedo, Mark Dickinson, Shelly Beauchamp, Christopher Jones

Peer Reviewed

Abstract:	The Very High-Frequency Omni-Directional Range (VOR) Minimum Operational Network (MON) Program plans to reduce the number of VORs in the National Airspace System (NAS) by approximately 30%. This reduction is in support of the transition to a more efficient Performance Based Navigation (PBN) routing structure that is consistent with Next Generation Air Transportation System (NextGen) goals and the NAS Efficient Streamlined Services Initiative (NESS). The primary role of the retained VORs is to enable pilots to revert from PBN to conventional navigation in the event of a Global Positioning System (GPS) outage. Conceptually, the Frequency Protected Service Volumes (FPSV) by the retained VORs provides adequate coverage. The coverage provides the ability to navigate and transition to an Instrument Landing System (ILS) or VOR Instrument Approach Procedure (IAP) at “MON” airports within 100-Nautical Miles (NM) of the aircraft’s current position (for altitudes ? 5,000-ft Above Ground Level (AGL)) at the onset of a GPS outage.[1] The FAA Spectrum Engineering and Frequency Assignment (AJW-1C2) group uses the Desiredto-Undesired (D/U) ratio for specifying the minimum geographical distance between two same or adjacent frequency sites within the NAS. The minimum separation distance depends on the individual sites’ maximum service volume (SV) radius including the associated service ceiling and their transmitter types, powers, antenna gains, and radiance patterns. When engineering frequency assignments, the minimum separation distance assures that aircraft within the frequency protected service volume of their intended navigational aid can navigate without radio frequency interference (RFI) caused by proximity to a nearby navigational aid. This paper focuses on the flight test and engineering analysis conducted for verifying the requirements for VOR/GBAS first adjacent (±25kMhz) channel protection (0dB D/U) published by ICAO EUR Doc 11, Sec 4.3. The flight test measures the first adjacent-channel interference conditions along a flight path at three different altitudes, 10,000, 14,500 and 18,000-ft Mean Sea Level (MSL) between a VOR and GBAS sites separated by 152-NM. The actual site separation is intentionally less than the minimum 224-NM distance required for protecting a Low VOR facility (i.e. 40 NM at 18,000-ft) and conversely a GBAS facility (i.e. 23 NM at 10,000-ft).[2] This test condition was set up for inducing interference data such that the engineering analysis can evaluate the actual D/U environment where the Multi-Mode Receiver (MMR) detects the interferer in relationship to the desired SV and the required 0dB D/U threshold. The engineering analysis uses these test results for determining the minimum separation distance for implementing the 70NM VOR MON frequency protection radius at 5,000-ft Above Transmitter Height (ATH) near an adjacent-channel GBAS.
Published in:	Proceedings of the 2017 International Technical Meeting of The Institute of Navigation January 30 - 2, 2017 Hyatt Regency Monterey Monterey, California
Pages:	705 - 713
Cite this article:	Etienne, Ernest, Hinton, Victor, Salcedo, Leonixa, Dickinson, Mark, Beauchamp, Shelly, Jones, Christopher, "Interference Testing of the 1st Adjacent-channel of the Ground-Based Augmentation System (GBAS) and the Very High Frequency (VHF) Omni-Directional Radio Ranges (VOR)," Proceedings of the 2017 International Technical Meeting of The Institute of Navigation, Monterey, California, January 2017, pp. 705-713. https://doi.org/10.33012/2017.14925
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