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

_______________________________________________
wsjt-devel mailing list
wsjt-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/wsjt-devel

Reply via email to