How to get rid of phantom signal from SDR?

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bubblegumpi
Posts: 49
Joined: Fri Oct 14, 2016 11:41 pm

How to get rid of phantom signal from SDR?

Postby bubblegumpi » Wed Mar 15, 2017 5:08 am

When ever I open my SDR the station it was last tuned to always has a phantom signal stuck on that location on the spectrum. When you tune up and down that signal always remains at that spot. Really annoying. In this screen shot I'm trying to pick up ADSb, which is strange I can't see it but there are 4-5 airplanes that I can pick up right now if I start dump1090.
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13dka
Posts: 125
Joined: Sun Feb 14, 2016 8:40 am

Re: How to get rid of phantom signal from SDR?

Postby 13dka » Wed Mar 15, 2017 6:41 am

bubblegumpi wrote:When ever I open my SDR the station it was last tuned to always has a phantom signal stuck on that location on the spectrum. When you tune up and down that signal always remains at that spot. Really annoying.


You're in 'Zero IF' mode. What you see is the DC spike that remains fixed on the LO frequency when you change the tuner frequency. Use 'Low IF' mode instead.

bubblegumpi wrote:In this screen shot I'm trying to pick up ADSb, which is strange I can't see it but there are 4-5 airplanes that I can pick up right now if I start dump1090.


You're tuned to almost 1091MHz (1090.97), with the lowest visible frequency on the spectrum being 1090.4MHz. Not much ADS-B to see there. :)

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bubblegumpi
Posts: 49
Joined: Fri Oct 14, 2016 11:41 pm

Re: How to get rid of phantom signal from SDR?

Postby bubblegumpi » Wed Mar 15, 2017 4:22 pm

13dka wrote:
bubblegumpi wrote:When ever I open my SDR the station it was last tuned to always has a phantom signal stuck on that location on the spectrum. When you tune up and down that signal always remains at that spot. Really annoying.


You're in 'Zero IF' mode. What you see is the DC spike that remains fixed on the LO frequency when you change the tuner frequency. Use 'Low IF' mode instead.

bubblegumpi wrote:In this screen shot I'm trying to pick up ADSb, which is strange I can't see it but there are 4-5 airplanes that I can pick up right now if I start dump1090.


You're tuned to almost 1091MHz (1090.97), with the lowest visible frequency on the spectrum being 1090.4MHz. Not much ADS-B to see there. :)


i didnt mean in that screen shot I was trying to pick up adsb. That screen shot was just to show the problem. Seems like there must be lots more signals but we just cant see them. dump 1090 says the signal level is -35 db
but its not visible in the waterfall.

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