Using SDRPlay as RFI Finder

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rons
Posts: 13
Joined: Mon Dec 14, 2015 6:03 pm

Using SDRPlay as RFI Finder

Post by rons » Fri Apr 29, 2016 2:16 am

I recently used my SDRPlay and SDRConsole to check out some 2M RFI. The RFI was so strong it could be heard in a scanner with the antenna removed, however the SDRPlay did not display the source (other signals were clearly visible).

Some online postings suggest that SDRPLay and/or SDR software may be optimized to remove RFI. This would normally be good, but not for my application. Does anyone have any recommendations to solve this issue?

Thanks, Ron
K2RAS
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DaveB
Posts: 142
Joined: Sun Feb 01, 2015 6:04 pm

Re: Using SDRPlay as RFI Finder

Post by DaveB » Fri Apr 29, 2016 10:28 am

My SDRPlay is excellent at showing up RFI. Some days at 0845 a dirty great RF source starts up at the lower end of the FM broadcast band - adding 25-30dB to the noise floor. It lasts about 45 minutes. It suggest to me an RF heating source when a factory starts up in the morning. Currently every evening about 20 mins after sunset something turns on and adds 5-10db noise and it shows as a series of humps roughly 200 kHz apart and stops about 20 mins before sunrise. Checking with a portable radio exhonerated nearby street lights - but there was a 30dB peak in noise from the bottom of a neighbour's garden when standing in the road outside. Sometimes I see what appears to be solar noise which peaks as the sun passes through one of the high angle lobes of the antenna.

I wonder if you are trying to track a similar wideband RF source - in which case you might need to look at the change in noise floor with the AGC turned off.
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F1BJB
Posts: 118
Joined: Wed Jul 15, 2015 4:24 pm
Location: Beauvais France

Re: Using SDRPlay as RFI Finder

Post by F1BJB » Fri Apr 29, 2016 1:11 pm

I think that SDRplay and other RTL dongles have a great advantage over various scanners for that purpose:
Their manual gain control and wide dynamic range.
Most FM receivers have no AGC at all.
Big sensitivity and wide frequency range are precious too.
I made a few experiments with magnetic loops as aerials on VHF.
They are very useful due to their small size and directional properties in vertical polarisation.
Some shielding can be required to make sure that only the loop receive the signal.
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13dka
Posts: 136
Joined: Sun Feb 14, 2016 8:40 am

Re: Using SDRPlay as RFI Finder

Post by 13dka » Sun May 01, 2016 8:10 am

1. If you receive something on one receiver but not on the other (with the same antenna), this would indicate that this something might not really exist -> internal imaging, "birdies"...

2. If you receive something noticeable on the scanner without any antenna that can't be received with some other receiver, this would strongly indicate that this is either a very, very local and short range RFI source* or (much more likely) your scanner is having "birdies", it's receiving its own oscillators if you will. Some radios do that, in particular badly shielded handhelds. That's half of the reason why scanners usually have a memory bank for skip frequencies and disconnecting the antenna is the usual procedure to distinguish these signals from real ones.

My Alinco DJ-X11 has hundreds of these birdies. What's even worse, it radiates a lot of that via the antenna, the casing or whatever, and that can be received just fine on another receiver in a distance of 10m or more. *For a reason along these lines it can be bad to stack receivers or generally putting them too close together at one spot and run more than one at a time.
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rons
Posts: 13
Joined: Mon Dec 14, 2015 6:03 pm

Re: Using SDRPlay as RFI Finder

Post by rons » Tue May 03, 2016 11:11 pm

I went back and the signal clearly disappears when I move more than 2 blocks from the approximate source, so I do not think that the signal is a 'birdie'. I am very confused about what to do next.

Any help is appreciated, Ron
K2RAS
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N4TKO
Posts: 15
Joined: Thu Apr 21, 2016 3:44 am

Re: Using SDRPlay as RFI Finder

Post by N4TKO » Thu Jun 02, 2016 4:40 am

i just used my SDRplay to identify a noisy SMPS in my apartment.... turns out it's the charger brick for my 2 meter HT....
i was running a 10 hour waterfall of the digi portion of 20 meters (14000-14150 khz), and i noticed on the waterfall that one of the annoying noise sources i've been putting up with actually shifted frequency as the day went by. knowing when sunlight usually is shining on this side of my apartment building, it looked like the frequency shift kind of followed the same pattern, so, thinking it might be affected by temperature turned on the heat to find out if this noise source was in my apartment. i really expected it not to show any change, because it really could be any apartment on this side of the building. after the heat being on a couple of minutes the curve reversed!!!!! so i began going through the apartment unplugging anything unimportant that has an SMPS in it... when i unplugged the charger for the HT, the noise vanished.... if i can, i'll post pics on the SDRplay yahoo group the waterfall and the spectrum display tell the whole story...

i do have a neighbor here somewhere that has an old CRT TV, and i can tell when they are watching it.... it's far noisier than the HT charger was (now if i can remember what i did with the analog wall wart i used to use with that HT)
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