I am right on the glide path for south bound aircraft to Tampa Intl A.P. about 50 miles north. Don't know if that has anything to do with the following observation. My radio is the Flex 6700 so have a panoramic view of the FT8 segment. Earlier last week during a strong Eskip session saw a station from Ga, 406 miles NNE, produce 4 sub-harmonic decodes Happened to be listening to the audio at the time and it sounded unusually musical. Looked over at the Pan and saw what appeared to be a station with unlimited sub-harmonics extending even below .313 The unusual amount of ghost signals only lasted on transmission. Sorry I don't have a screen shot or saved .wav file.
Now that the ghost signals have been identified and reported seems they are quite frequent. Has anyone else noticed such a strong flurry of ghost signals? Bill W2PKY On Sat, Jul 13, 2019 at 9:29 AM Conrad PA5Y <g0...@g0ruz.com> wrote: > It does, Joe. > > Thanks for the first convincing explanation that I have seen. > > Regards > > Conrad PA5Y > > -----Original Message----- > From: Joe Taylor <j...@princeton.edu> > Sent: 10 July 2019 01:41 > To: WSJT software development <wsjt-devel@lists.sourceforge.net> > Subject: Re: [wsjt-devel] FT8 ghost signals > > Hi Conrad, > > On 7/8/2019 18:29, Conrad PA5Y wrote: > > In fact Martin, sometimes they clearly AP reflections are but often they > are not. They have no discernible doppler slant at all and appear to be a > fixed offset and have me completely puzzled. I regularly see 2 or 3 'ghost' > signals between 6 and 20dB lower in amplitude than the main signal on 2m > from stations with 100W to a 9ele or more. Stations can be several hundred > km away from me. The offsets vary between 70-150 Hz and can be positive or > negative. In order to have a doppler shift something must be moving and > with an offset of 100Hz or more quite quickly. You would think therefore > that the frequency offset would change and it often does not but remains > static for several periods and then just disappears. How on earth can this > happen? I have no reasonable explanation for it but I assure you it is real. > > > > Aircraft scatter on 6m occurs of course but not so often, however during > intense Es events sure enough I also see these ghosts on 6m and again no > shift. It really is very puzzling indeed. > > Evidently what's puzzling you is Doppler shifts that remain nearly > constant for a minute or so. Aircraft at 10,000 meters can be > line-of-sight visible at distances up to several hundred km. With typical > aircraft speeds, in such cases the geometry for bi-static reflections will > not change much over a minute. So the Doppler shift can remain nearly > constant. Does this not make sense? > > -- Joe, K1JT > > > _______________________________________________ > wsjt-devel mailing list > wsjt-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/wsjt-devel > > > _______________________________________________ > wsjt-devel mailing list > wsjt-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/wsjt-devel >
_______________________________________________ wsjt-devel mailing list wsjt-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/wsjt-devel
