LOTS of interference in direct sampling mode

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Geogems
Posts: 2
Joined: Wed Oct 24, 2018 12:05 pm

LOTS of interference in direct sampling mode

Post by Geogems » Wed Oct 24, 2018 12:11 pm

Hello guys,
I was wondering if all those interference I see in the waterfall are something I should expect or if the dongle is malfunctioning. As you can see in the picture the waterfall is full of interference "spikes", but also ghost signals and mirrored signals.
I am using a 10 meter dipole antenna made out of speaker wire, outside in a public park in Ottawa. The antenna is hang between two trees, 1.5m above the ground. The dongle is attached to a 6 feet USB-3 cable, away from the compute

The weird thing is that I think I remember the first time I used the direct sampling mode with this antenna in the same place there was muuuch less interference spikes. I am worrying the dongle may be broken by an esd or something. Quadrature sampling works well tho.

I also posted my problem on reddit but I wanted to have a second opinion.
Any thoughts?

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rtlsdrblog
Site Admin
Posts: 2160
Joined: Mon Nov 19, 2012 11:54 pm

Re: LOTS of interference in direct sampling mode

Post by rtlsdrblog » Thu Oct 25, 2018 10:47 am

What does it look like on regular broadcast AM? Can you see signals there?

And is your antenna protected against ESD? ESD damage is possible if you are using an unprotected outdoor antenna. Please remember that as with all radios there should be ESD protection on any permanent outdoor antenna. The ESD diodes in the dongle can only handle so much, and wont handle high ESD or nearby lightning strikes.

Geogems
Posts: 2
Joined: Wed Oct 24, 2018 12:05 pm

Re: LOTS of interference in direct sampling mode

Post by Geogems » Thu Oct 25, 2018 12:11 pm

I only see some random AM stations here and there, nothing very busy like in the FM band.
My antenna is just a long speaker wire dipole I bring with me and hang up between two trees when I go to the park. It is unprotected.

rtlsdrblog
Site Admin
Posts: 2160
Joined: Mon Nov 19, 2012 11:54 pm

Re: LOTS of interference in direct sampling mode

Post by rtlsdrblog » Sat Oct 27, 2018 7:04 am

To me it doesn't seem like ESD damage. Usually if there is ESD damage you'll get no signals.

Do you receive the same interference with no antenna connected?

If you don't then II think you've just got some strong interference from something which is blocking your signals nearby.

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