Hi Rich, I’ve observed the same, exactly as you described. Had put it down to urban reflections, perhaps more obvious when W3/W4 is beaming N/NE. Agree with you they are not aircraft scatter.
George J Molnar Arlington, Virginia, USA (702) 767-5420 KF2T - FM18lv > On Jul 6, 2019, at 4:06 PM, Rich Zwirko - K1HTV <k1...@comcast.net> wrote: > > > Here in the Mid-Atlantic, a number of 6 Meter FT8 DXers have observed > backscatter signals that appear as a 2nd or even a 3rd signal on the WSJT-X > Wide Graph window. The Doppler shifted frequency is usually lower than the > direct signal. In addition to the directly received FT8 signal appearing on > the waterfall display, at times both direct signal as well as one or more of > the reflected backscatter Doppler shifted signals can be decoded. The DF > between the main and ghost signals is usually between 40 and 130 Hz. The > average appears to be around negative 70 Hz. > > When these ghost signals are observed, they are usually noted on multi-KW FT8 > signals produced by stations in the Mid-Atlantic region that are beaming > towards highly ionization Es regions. These extra waterfall signals can last > a few minutes then quickly disappear. I have not observed them when there is > no Es opening. They don't appear to be the result of signals being reflected > off aircraft. > > 73, > Rich - K1HTV > > = = = > > From: Jim Brown [mailto:k...@audiosystemsgroup.com > <mailto:k...@audiosystemsgroup.com>] > Sent: 6. heinäkuuta 2019 9:28 > To: wsjt-devel@lists.sourceforge.net <mailto:wsjt-devel@lists.sourceforge.net> > Subject: Re: [wsjt-devel] 60 Hz + harmonics sidebands on FT8 signals? > > There are two common causes of sidebands with a station that is properly > adjusted and uses good equipment. > > 1) The best gear (Elecraft K3, K3S, or a Flex 6000-series), and a first class > power amp) have sidebands roughly 40 dB down on both sides of their signal > due to IM distortion in the RF stages. These sidebands are generally > symmetrical, and the total -40 dB bandwidth is about 680 Hz. > > 2) Doppler shift produced by reflections from aircraft. These sidebands are > generally asymmetrical (that is, on one side or the other of the main > signal). Here in the SF Bay Area, which includes Silicon Valley and extends > down along the Monterey Bay, we have glide paths for major airports in San > Jose and San Francisco. > > There are roughly a dozen or so locals running 500W with gear like this, and > we all regularly experience what you're seeing. > > 73, Jim K9YC > _______________________________________________ > wsjt-devel mailing list > wsjt-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/wsjt-devel
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