VDL Mode 3 Cosite Interference Testing Summary

GPS Emissions DO-271A MOPS Insufficient to Ensure Non-Interference to GPS Existing Mode 2 Transceiver Emissions Measured – Very Small Margin of Safety With Some Transceivers Boeing Recommends Revising DO-271A to Reduce Allowed VHF Emissions in GPS Band

Proposed Emissions Limits in GPS Band from VHF Transceiver Current DO-271A CW Limit: -60 dBM Proposed CW Limit: –70 dBM Current DO-271A Broadband Limit: Not Specified Draft ED-92A Broadband Limit: -60 dBM over a 100 kHz bandwidth Proposed Broadband Limit: -68 dBM over a 100 kHz bandwidth

DME Emissions DO-271A MOPS Insufficient to Ensure Non-Interference to DME Existing Mode 2 Transceiver Emissions Measured – Very Small Margin of Safety With Some Transceivers Boeing Recommends Revising DO-271A to Reduce Allowed VHF Emissions in DME Band

Proposed Emissions Limits in DME Band from VHF Transceiver Current DO-271A CW Limit: -16 dBM Proposed CW Limit: –60 dBM Current DO-271A Broadband Limit: -36 dBM over a 100 kHz bandwidth, 960 MHz - 1000 MHz, not specified above 1000 MHz Proposed Broadband Limit: -60 dBM over a 100 kHz bandwidth, 960 MHz – 1215 MHz

Comparison of GPS and DME Emissions, Mode 2 and Mode 3 MOPS for Mode 2 and Mode 3 have equivalent emissions limits – Mode 3 transmitting on a particular frequency is expected to have equivalent interference to Mode 2 on the same frequency Mode 3 is expected to operate anywhere in the comm band, whereas Mode 2 is currently operating only on 136.975 MHz Harmonics of the existing Mode 2 frequency do not fall in the GPS receive band, but Mode 3 is expected to use frequencies with harmonics in the GPS receive band

VHF to VHF Interference Analysis, testing indicate insufficient isolation exists between VHF antennas to preclude interference Receive distance is reduced when another VHF radio is transmitting on the same airplane Receive performance degradation depends on RF circuitry in radio and frequency separation Squelch breaks occur on adjacent channels

Maximum Receive Distance vs Maximum Receive Distance vs. Frequency Separation Boeing Limited – Do Not Distribute Outside FAA

Other Considerations in Evaluation of VHF to VHF Interference Flight crew coordination – in traditional DSB-AM, interference occurs as a result of keying microphone; other pilot can request a halt to transmissions if interference is noticed Relatively few digital (automated) communication frequencies in current environment; automated digital systems are unaware of interference and the flight crews do not have direct control over when the interference occurs

Other Considerations in Evaluation of VHF to VHF Interference Difficult to recognize degradation in receive performance; flight crew may not hear ATC clearance due to simultaneous transmission to a company frequency or ACARS datalink transmission on board the airplane – ATC standard practice of repeating the clearance may result in no awareness by the flight crew that ATC clearance was blocked

Mode 3 Polling Response Two manufacturers of transceivers tested using 800 kHz channel spacing and antenna isolation equivalent to two antennas on same side of aircraft No interference noted from one manufacturer, but noticeable interference sounding like pops or clicks were heard when testing the other manufacturer Speech was intelligible in presence of interference