Reducing Radio Noise

Radio Frequency Interference (RFI) is one of the enemies of a good clean signal. We can sometimes do things to reduce the impact of RFI and the following are things that have worked for me in the past.

Switch off Monitors
If you see lines on your radio display which disappear when you power off the monitor (or any other monitors near it) then you're getting RFI from there. A simple fix is to run most of the time with monitors off, because the monitor screen can give off a lot of RFI. That said, it usually has just a short range so moving the SDR further away from your PC frequently helps here. Some use a USB extender and they can be found with 30 metre lengths! Those could be used to put your SDR at the antenna and get rid of coax altogether.

Noisy Power Blocks
I found that I had one power block (4-way 240V AC) that while working fine as a power extender, was giving out a ton of RFI. I found it by switching off power to each thing in the room until the radio spectrum showed less noise. I labelled that up as RF Noisy and put it elsewhere in the house.

Earthing SDRs
This one seems to work for some but not others. Fastening a wire to earth from the case of your SDR sometimes reduces noise, sometimes increases it. YMMV. I run a rapsberry pi 3 with an airspy and with the pi on wifi it's very quiet RFI-wise. When I put a wired cat5 cable into the ethernet port all hell breaks loose. Some have said their's aren't affected this way so it may be a batch issue. I intend to fix it by placing the pi into a die cast metal box and see if that helps.

Ferrite Beads
These are cheap iron blocks that you can attach to the outside of cables to reduce the effect of RFI travelling down the cable to the receiver. They can work for RF, USB or for power cables and as they're cheap it's always a good idea to have some handy to test with.

Antenna Placement
If your antenna is co-located with another that transmits then you could be in trouble again there. By transmit I mean if the other antenna intentionally transmits (pager towers, FM broadcast radio, ACARs etc) or if it's a neighbours Sat TV antenna that points directly through yours. In the case of the latter then the issue seems to be the RF amp in the antenna is pushing signal back out into the received path. All receivers leak a little rf energy back out but it's not normally noticable. It may be noticable if your wxsat antenna is right in it's local path. Moving either antenna should help.
If the issue is with pagers, then siting your antenna in a radio shadow from the pager tower may help. On the other side of your house for example. Some use a narrow band filter (sometimes built into a Low Noise Amp) near the antenna or next to the radio and report success from FM Broadcast interference.

Finally there's an excellent article HERE that appeared in the old RIG newsletter. It's a very graphic way to home in on your problem.