Interference from PC - What is it causing?


after wondering about the waveform in my signallog, I now found out that my PC, that is in the same room, but some meters away, is interfering with the DIY receiver. The Receiver has NO physical connection to the desktop and is even plugged into another outlet.

When my PC is on, i get around 2,5-3,5 db SNR in the Moment, If i turn it off, my SNR shoots up to over 7db!

I already removed any device from my PC that can transmit (Bluetooth, wireless mouse, xbox wireless adapter), but that does not help at all.

Does anyone has an idea what can cause ther interference?



Yo tengo un monitor CRT que produce muchas interferencias, también puede ser la fuente de alimentación, muchas no tienen los filtros adecuados, también puede ser el disco duro si no está atornillado a la caja del ordenador en contacto con el chasis (esto también me ha pasado).

El PC es una fuente inagotable de interferencias.


I have a CRT monitor that produces a lot of interference, can also be the power supply, many do not have the proper filters, can also be the hard drive if not screwed to the computer box in contact with the chassis (this also has me past).

The PC is an endless source of interference.

I know…i hope i can find the part or shield the Receiver enough :slight_smile:

The Monitors (both tft) are not causing the problem, that was my first guess.
But what can make such a strong interferance that it is causing problems in the receiver 3m away?


Shield the LNA using some sort of metal enclosure, or carefully wrap it with plastic, then aluminum foil. It could very well be the monitor, rather than the PC, that is causing the interference.

Since you ruled out your monitor then it is most likely your pc power supply. You might be better off shielding your receiver, however a power supply making that much noise may be failing.

since you have ruled out the displays ( bu completely un-powering them I assume) then as was stated above , it is 99.9% sure it is the power supply.

Assuming that the power supply is not failing ( which may be the case!) you didn’t say if it was a desktop or a laptop…

If it is a laptop, then see if the noise goes away when it runs on battery… if so, then try another power supply ( not a cheap generic one!) put toroids both ends of both the AC lead and the DC lead, maybe wrap the plastic case of the PS on foil and ensure it is grounded ( put your hands tightly around it when it is on & see of the noise reduces, that will give you a clue if you should try shielding the case.) I t is important to not that 99% of laptops are NOT grounded, and that makes shielding more difficult!

If it is a desktop and you are NOT using a grounded AC lead ( I don’t know what is normal in the US) the you should be! 3 pins in the wall and 3 pins at the PC case! If is not grounded then ground the metal frame of the PC. and you may find your problem goes away like magic :slight_smile:

As for shielding the LNA… I simply covered min in bubblewrap ( to keep the foil a decent distance away from the board so I didn’t make capacitance issues) and wrapped it in aluminium foil, that is “caught” in the thread of the SMA connector at one end. Made a big difference to “stray” noise

Good luck… I still have noise issues from a local LNA on a steerable satellite dish, but that is picked up outside by the antenna!

Thanks for all the replys.

I am using a desktop and the power supply is only 1 year old and a brand one. Here in Germany, there is no other way then using a grounded AC lead :slight_smile:

I tested some things last night, and i found out that the gpu is interfeering with the Receiver. When it is under heavy load, the SNR gets lower in comparision to a low load (only displaying the desktop). I think that the coils in the gpu are the problem.

I will shield my LNA now, i hope that helps. I already tested the bubblewrap method, but it had not helped.


PS: I am working as a Software Developer, so i know PCs quite well. The replys can be more complicated :wink:

Is the PC in a metal case? If not then a new case would be good :slight_smile:
The graphics board SHOULD have shields over the critical parts… There is little regard for RFI these days :frowning:

If it is a discrete Graphic board in the PC, then the “bubble wrap & foil” actually IN the PC case and around the graphic card would probably work, ensuring that the foil is grounded, of course . The card may overheat though… that would solve you problem too! LOL!

xD :joy:

I could wrap my whole pc in aluminium foil :wink:

Of course the case is metal :slight_smile:

LOL. Foil the answer to everything :slight_smile:

A lot of the “gamers” cases have only a metal frame and the panels of the case are just plastic… so I had to ask! :slight_smile:

I never saw any case that has plastik sides xD

my case has a window, but the rest is metal. My case

I now shielded my LNA and it got a little bit better. But its still a difference of around 2-3db SNR between pc On / Off.
(Iook at that depth of field :wink: shot with Oppo Find 7a)

Great DOF LOL!

Don’t know if you saw my comment on the 1.0 thread. I had interference from my TV and the biggest improvement came from looping the usb able through snap-on ferrites on both ends (power supply and CHIP). I also shielded the pre-amp and fiddled with the arrangement (i.e. pointing the antenna higher up beyond the satellite direction). It used to knock out Outernet despite good reception, now I have 7-9 dB independent of the TV being on at exact same place as before.

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Yeah i saw your post, because of that i testet my monitors first :slight_smile:

I will buy some ferrites to test that.


Don’t forget about the pliers. :slight_smile:


I actually was thinking about that :smile:

I tested the Receiver with a powerbank, and the same happens. So it is not comming from the AC line or Power supply.

Ferrites are also already ordered.

Interference coming in from the power line was my first thought. I hooked up a USB battery and it didn’t make a difference. So I went back to the USB power supply. Still, when I added chokes to the USB cable it made it much better. Possible the USB cable still catches interference when connected to a battery?

Mira lo que he tenido que hacer yo en mi ordenador, ya te digo que el ordenador es una fiesta de grillos.

Y aun así la eliminación de casi todas las interferencias ha sido alejando la antena y el LNA lo máximo posible.

He pensado que la gran mayoría de interferencias entra por la antena, he intentado poner el E4000 en la misma caja que la antena y el LNA, y me daba menos SNR que alejado de la antena con 5 metros de cable LMR400, lo que indica que el E4000 mete interferencia a través de la antena, he probado con el mismo SDR que tienes tú y he obtenido el mismo resultado, lo que me indica que la antena es propensa a recoger mucho ruido.

Has probado a girar la antena?


Look what I had to do on my computer, I tell you that the computer is a party of crickets.

And even so the elimination of almost all the interference has been moving away the antenna and the LNA as much as possible.

I have thought that the vast majority of interference goes through the antenna, I tried to put the E4000 in the same box as the antenna and the LNA, and it gave me less SNR than away from the antenna with 5 meters of LMR400 cable, which indicates that The E4000 puts interference through the antenna, I have tested with the same SDR that you have and I have obtained the same result, which indicates that the antenna is prone to pick up a lot of noise.

Have you tried turning the antenna?

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Thats not a PC anymore, it’s a big ferrite :smile:

I will use my ferrites only on the Receiver, it should be enough.

Turning the Antenna? The Antenna is pointing away from the pc, slightly off the sat to get Signal between the other buildings.


PS: My ferrites where send out today. should arrive this week :slight_smile:

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For interference hunting I strongly advise you QSpectrumAnalyzer, can run a nice wide plot from 50 to 1700 MHz:

You can run it on a RPi 3 or Linux PC. Use the RTL-SDR V3 dongle from the kit and any antenna (the Outernet patch is good too but it will selective on L-Band). Remove the LNA or ahead start the bias tee from software: