"Doppler caused "spreading" is readily identified ... the spreading is generally in one direction (because airport "patterns" run in one direction) and often manifests as a second signal offset by 60-80 Hz (which can be independently decoded). IMD is generally in both directions and can not be decoded."
The aircraft that can be expected to cause Doppler shifted reflection in the Phoenix Class B airspace are transport aircraft following Standard Instrument Departures (SID) and Standard Terminal Arrival Route (STAR) routings. My QTH is about a mile from a KPHX STAR (BRUSR ONE). On a busy day with winds out of the East they go by at about one per minute. As they approach from the North I would expect reflections with a higher frequency. After they pass and move to the South I would expect reflections with a lower frequency. With multiple aircraft following the same route I would expect a mix of reflected signal frequencies spread on each side of the transmitted signal frequency. If my calculations are correct an aircraft would have to be moving at 700 kts to give a Doppler shift of 60 Hz. Metro area airports are usual in Class B airspace with a speed limit of 250 kts. Maximum speed on the BRUSR ONE is 250 kts reducing to 210 kts as they pass my house. At 250 kts I calculate a shift of 22 Hz. I assume one of us has a math error. I'll be happy to correct my spreadsheet if my numbers are wrong. I couldn't find any screenshots of Doppler shifted FT8 signals. I'll look out for some next time there is activity on 6 m. 73, Andy, k3wyc ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
