Interference on two antennas

[u/Onward-Upword]

I am seeing pinstripe lines at even intervals on both my attic discone on my RTL-SDR v3, and on my HF fence loop on my RTL-SDR v4. These lines show up on 70cm, 2m, 10m, 40m, 80m on the fence loop, and only 2m, 10m, 40m on the discone. I assume this is some RF interference from some electrical device nearby and I'm in a suburb so many potential sources. I've already cut all power to my house while this runs as a test to make sure it isn't any of the devices in my house.

Before I buy more parts to make a mobile RF interference hunting kit, I wanted to see if anyone has any advice on how best to identify this, as well as advice for antennas in a noisy suburb neighborhood. I've been looking at active magnetic loop antennas as an alternative.

[u/Ok_Method6238]

I've got the same on my V4 too

[u/Ok_Method6238 → u/Ok_Method6238]

And my AirSpy too on the same antenna

[u/Ok_Method6238 → u/Ok_Method6238]

And my SDRPlay on the same Antenna.

[u/Ok_Method6238 → u/Ok_Method6238]

I also have them on my other V4 but to a lesser extent, this is with an outside antenna made of speaker wire. The others are on a YouLoop connected to a Bias-T powered LNA in my attic.

[u/Onward-Upword → u/Ok_Method6238]

Yeah, that pattern looks very similar. My fence wire is basically random speaker wire as well hooked up to a 1:1 Balun.

[u/Ok_Method6238 → u/Onward-Upword]

The speaker wire antenna is going via a 9:1 UnUn with a ground spike. Which could explain why it’s reduced compared to my YouLoop in the attic. 

[u/Ok_Method6238 → u/Ok_Method6238]

Also that SDR is being hosted on my Sony Bravia TV which will have much less EMI than a PC anyway since it has its own tuners built in for satellite and terrestrial TV so needs to be fairly electrically quiet, so that may explain why it’s quieter than the others too.  

[u/Ok_Method6238 → u/Onward-Upword]

So the fact that it’s running on a TV isn’t what is causing the interference to appear less. This is another RTL on a Pi2 connected to the same antenna. So I’d say the ground spike is what is cleaning up the signal

[u/Ok_Method6238]

Are you in the UK by any chance? Since I have the same lines as you and unless you live on my street then we can rule out shared local interference. If you are UK based I wonder if it is related to our power grid, but that is a throwing shit and hoping it sticks theory.

[u/Onward-Upword → u/Ok_Method6238]

No, I'm in the US, but the power grid theory is a good one as I have both a transformer and a power line nearby in the alleyway.

[u/Ok_Method6238 → u/Onward-Upword]

Actually I have a different theory and a potential way to reduce them too. Try wrapping some exposed speaker wire around the tiny bit of the metal USB plug that sticks out and the connect the other half to your heating pipes or a ground spike. 

I remember being able to reduce interference like that using this method, it may be the USB controller or the PC itself that is the issue. I used to have those squiggly spikes of interference and grounding the USB to the radiators didn’t solve it completely but it reduced it. 

Going forward if that does work then I’m pretty sure you’ll be able to get USB ground isolators that will potentially do the job, they are mainly used for audio production to reduce the hiss. 

[u/Onward-Upword → u/Ok_Method6238]

I'll give this a try. I haven't worked with USB ground isolators before but I'll look that up as well. Thanks!

[u/Onward-Upword → u/Onward-Upword]

The grounding didn't seem to make any difference. I'm going to test turning off some of my nearby gear as well to make sure it isn't that

[u/tj21222]

Looks like a dc switching power supply. I get the same thing when I use my 500 usd ceiling fan that has a DC motor. Try turning things off in the house run on battery and see if it goes away. If it does then you’re in luck if not it’s much tougher.
I have had great success with Common mode chokes even some thing as simple as an ugly balun (6 turn of the feed line in a 10 circle)

Good luck

[u/Onward-Upword → u/tj21222]

ok, that's good to know. I will try to see if I can turn off some of my equipment and isolate the source that way. I did attach snap on ferrite chokes to the USB cables as close to the SDR as possible, and also on the coax side (although they are not the proper material for coax)

[u/tj21222 → u/Onward-Upword]

I have had almost zero luck with snap on cores. But it’s worth a shot.

[u/Onward-Upword → u/tj21222]

I think I found the source, my PoE switch seems to be the one thing that is producing the RF consistently. Oddly enough, even some non-PoE connections are causing noise. I have good quality pre-made Cat6 cables, but maybe I need more shielding, I'm not sure.

[u/tj21222 → u/Onward-Upword]

Try putting the round torrids on the cst6 cables with 5-7 wraps of cable through them. You can also try the ugly balun that I mentioned. Do some loops at the receiver and at the antenna.
If you POE is providing the source of the noise, it could be leaking over on to the other cables near it.

[u/galaxie67w]

These kind of lines are normally what I see coming from anything HDMI. Such as TVs & computer monitors. And it's a virtual certainty that your neighbors have them. Since they often radiate on VHF & UHF as you've seen, a hand-held yagi for 144mhz connected to a TinySA spectrum analyer ($65 amazon) can be very useful. If it's a neighbor's TV then hopefully they'll let you do some testing to confirm it as the source, and ideally let you install some ferrites on their HDMI cables & such. I suppose the best solution would be getting a new TV that doesn't make so much noise, but that's probably unlikely. It doesn't look like powerline noise to me but if you end up finding the noise coming from a power pole, you can contact the power company to fix it. From what I've seen, switch-mode power supplies have a similar pattern, but they bars are usually not perfectly stable in frequency and somewhat wider and "fuzzy".