Bad RFI from Computer?

LunaEros

Member
Premium Subscriber
Joined
Jul 19, 2021
Messages
9
Location
Hickory, NC
Hoping someone can help me. I have the RTL-SDR v3 connected with rg58 to a double sized mobius loop outside about 8-10 feet up and am getting bad RFI most prominent around 3mhz and around 25-26mhz but it's all therough the spectrum to a lesser extent. It looks like a sawtooth pattern and sounds like high voltage buzz. I think it's from my desktop. I think that because the computer also somehow generates MAJOR RFI at about 143.995mhz. I know this because I have a Kenwood 2m right and it disappeared when I turned the PC off. I'm including the screenshots and links to the baseband and a short audio file to see if anyone recognizes what kind of RFI it is. If it is the computer does anyone have any suggestions on how to stop it generating rfi? I did put those ferrite snap on cores on pretty much all the cables but it didn't seem to help. I can still get signals as long as it isn't in the midst of the interference but it's ruining my trying to enjoy lower band listening since I can hear it to some extent through most of the spectrum.

Basebands: RFI Basebands.wav
Short Audio: RFI Audio.wav
 

Attachments

Ubbe

Member
Joined
Sep 8, 2006
Messages
6,102
Location
Stockholm, Sweden
You can probably move that interference to either side by changing the PC screens update frequency, lets say from 70Hz to 60Hz if it is in the middle of something you would like to monitor. Also a standard RG58 have very bad shielding and let those interferencies pass thru the braid. Use RG6 or similar with a braid and a foil that attenuates outside signals more than 100dB.

/Ubbe
 

a417

!#
Joined
Mar 14, 2004
Messages
2,231
Hoping someone can help me. I have the RTL-SDR v3 connected with rg58 to a double sized mobius loop outside about 8-10 feet up and am getting bad RFI most prominent around 3mhz and around 25-26mhz but it's all therough the spectrum to a lesser extent. It looks like a sawtooth
try to get a USB extension cable and move the dongle away from the main chassis of the computer, into a little homebuilt faraday cage if you are really so inclined. Those dongles themselves aren't the best at keeping stray RFI out.
 

LunaEros

Member
Premium Subscriber
Joined
Jul 19, 2021
Messages
9
Location
Hickory, NC
You can probably move that interference to either side by changing the PC screens update frequency, lets say from 70Hz to 60Hz if it is in the middle of something you would like to monitor.
/Ubbe
Fairly positive it's not the monitor. I shut the monitor off while I was troubleshooting and listening to it and it was still there with it off.
Gonna try a couple other things such as turning the Bias-T off since I recently had it turned on when I got an LNA for it. And yes I tried pulling the LNA back out but it didn't change. But I did forget to turn the Bias-T off when I did. I also have 2 others I use for VHF and am gonna try those. They have a discone on those. If those don't have the RFI I'll change the mobius over to them. That should tell me if it's the antenna or the RTL I'm using for HF and lower.

Nobody recognizes what kind of RFI that looks and sounds like?
 

popnokick

Member
Premium Subscriber
Joined
Mar 21, 2004
Messages
2,274
Location
Northeast PA
I think it's from my desktop. I think that because the computer also somehow generates MAJOR RFI at about 143.995mhz. I know this because I have a Kenwood 2m right and it disappeared when I turned the PC off.
... then it IS very likely the PC, specifically the switching power supply used by the PC. Try a different computer / laptop, or change the power supply used by the PC. Other possibility is a cable modem or Ethernet switch / router. But because it goes away when you turn off the PC... that pretty much points to the PC, don't you think?
 

ecps92

Member
Joined
Jul 8, 2002
Messages
12,174
Location
Taxachusetts
instead of turning off the monitor, unplug it from the outlet

Many devices, altho the power switch is off, still have power going to them and can/do cause RFI
Fairly positive it's not the monitor. I shut the monitor off while I was troubleshooting and listening to it and it was still there with it off.
Gonna try a couple other things such as turning the Bias-T off since I recently had it turned on when I got an LNA for it. And yes I tried pulling the LNA back out but it didn't change. But I did forget to turn the Bias-T off when I did. I also have 2 others I use for VHF and am gonna try those. They have a discone on those. If those don't have the RFI I'll change the mobius over to them. That should tell me if it's the antenna or the RTL I'm using for HF and lower.

Nobody recognizes what kind of RFI that looks and sounds like?
 

Chronic

Member
Joined
Nov 7, 2004
Messages
483
Fairly positive it's not the monitor. I shut the monitor off while I was troubleshooting and listening to it and it was still there with it off.
Gonna try a couple other things such as turning the Bias-T off since I recently had it turned on when I got an LNA for it. And yes I tried pulling the LNA back out but it didn't change. But I did forget to turn the Bias-T off when I did. I also have 2 others I use for VHF and am gonna try those. They have a discone on those. If those don't have the RFI I'll change the mobius over to them. That should tell me if it's the antenna or the RTL I'm using for HF and lower.

Nobody recognizes what kind of RFI that looks and sounds like?
Just because the monitor is turned off , does not mean the video card is not still sending a signal to the monitor.
 

iMONITOR

Member
Premium Subscriber
Joined
Sep 20, 2006
Messages
9,601
If it is the computer does anyone have any suggestions on how to stop it generating rfi?
Do you have a home network and if so are you using good quality cables? Are your USB cables shielded and have RF beads (chokes) on them? Is all your computer hardware plugged into three prong grounded outlets?
 

TomLine

Member
Premium Subscriber
Joined
Jul 22, 2019
Messages
45
Location
Hamilton, Ohio
What kind of antenna setup are you using? Have you tried others? Kind of looks like broadcast band overload? Are you using quad sampling or direct sampling? My rtl-sdr requires shifting from quad to direct sampling to get below 24 mhz or so. I got a couple AM and FM broadcast band filters I use sometimes. (If it's the cat5 cables, you can power down the repeater / disconnect them to see if there's a change. They can emit spike signals a ways apart, but not necessarily the big underlying wave.)
Whoops, just re-read your post. Do you have slugs or a common mode loop in your antenna line?
 
Last edited:

LunaEros

Member
Premium Subscriber
Joined
Jul 19, 2021
Messages
9
Location
Hickory, NC
Well I found that the other RTLs don't make the noise. Just the first one. And it seems only when the BiasT is turned on. It doesn't make itwhen it's turned off. The other RTLs don't respond the same way. There's no RFI when those have it turned on. Did I possibly get a bad RTL with the first one I got? Will RTL-SDR.Blog exchange it for a new one since I bought it at the end of July?
 

TomLine

Member
Premium Subscriber
Joined
Jul 22, 2019
Messages
45
Location
Hamilton, Ohio
I'll try my two RTLs and see if they show different noise characteristics. I know they had different revisions of the RTL's, but the paint wears off quick and it's difficult to tell which I have. They bend at the connector from heat and torque. I wonder if the circuit traces or components get wonky from that.
 

paulears

Member
Joined
Oct 14, 2015
Messages
490
Location
Lowestoft - UK
In my office, one of the channels I routinely monitor is marine channel 8. It is fine until I run Adobe Premier on one of the computers. It isn't running the application, it's when I put the programme monitor on the 2nd screen - as soon as that screen runs video - ch 8 is wiped out with buzz - very loud buzz. it's a big spike on 156.4MHz - and my scanner hears it too. It's also linked to the video format. Old SD projects don't do it, but all the HD ones kill the radios. Is that bizarre or not!
 

iMONITOR

Member
Premium Subscriber
Joined
Sep 20, 2006
Messages
9,601
Well I found that the other RTLs don't make the noise. Just the first one. And it seems only when the BiasT is turned on. It doesn't make itwhen it's turned off. The other RTLs don't respond the same way. There's no RFI when those have it turned on. Did I possibly get a bad RTL with the first one I got? Will RTL-SDR.Blog exchange it for a new one since I bought it at the end of July?
What are using to supply power to the BiasT?
 

lwvmobile

Member
Joined
Apr 26, 2020
Messages
231
Location
Lafayette County, FL
In my office, one of the channels I routinely monitor is marine channel 8. It is fine until I run Adobe Premier on one of the computers. It isn't running the application, it's when I put the programme monitor on the 2nd screen - as soon as that screen runs video - ch 8 is wiped out with buzz - very loud buzz. it's a big spike on 156.4MHz - and my scanner hears it too. It's also linked to the video format. Old SD projects don't do it, but all the HD ones kill the radios. Is that bizarre or not!
Could it be due to you putting the PC under a heavy workload, requiring it to draw more wattage from your power supply, making it work harder, along with your CPU and GPU? Also, under load, many PC will start to spin their CPU and GPU fans faster in order to keep the temperature down, so could be getting increased EMI from those fans as well.
 

rabbit108

Member
Joined
Jan 4, 2021
Messages
158
Location
S.E. VA
Well I found that the other RTLs don't make the noise. Just the first one. And it seems only when the BiasT is turned on. It doesn't make itwhen it's turned off. The other RTLs don't respond the same way. There's no RFI when those have it turned on. Did I possibly get a bad RTL with the first one I got? Will RTL-SDR.Blog exchange it for a new one since I bought it at the end of July?
The Bias-T was changed between V2 and V3.

RTL-SDR previous and latest pcb_1.jpg
Review: rtl-sdr.com v.3

rtl-sdr-annotated-5_1.jpg
RTL-SDR V3 Teardown and Analysis - OnElectronTech

rtl-sdr-frontend_1.jpg

Bias-T Section: Contains a voltage regulator and an RF-blocking inductor to inject power, or “bias”, the RF input. Useful for powering amplifiers or other active components connected to the RF line, without the need for additional power supplies. Note the resettable fuse (black component labeled T02), which protects the Bias-T from overload.
NOTE: I don’t recommend taking apart your RTL-SDR unless it’s absolutely necessary. There’s a silicone thermal pad on the bottom that contacts the board and the case, and it’s best not to disturb it. I did this so you don’t have to!
 
Last edited:

Spleen

Active Member
Premium Subscriber
Joined
Dec 19, 2002
Messages
904
Location
Baltimore, MD
Read this thread through and then remembered years back when after hours of investigating, I discovered that the power strip I was using was basically a RFI antenna/transmitter set. It was a good excuse to put it in the e-cycle bin and spring for the UPS unit I should've been using anyway...
 

LunaEros

Member
Premium Subscriber
Joined
Jul 19, 2021
Messages
9
Location
Hickory, NC
What are using to supply power to the BiasT?
The BiasT is powered by the RTL itself. When it's turned on it sends power back out the antenna cable to power things like preamps and such.

.....and spring for the UPS unit I should've been using anyway...
That's another thing I've got to do. I have a Cyberpower 800 that I got new batteries for a while back and it runs fine but for some reason if it has something plugged into the battery backup outlets it will turn off after a while. Otherwise it stays on. And the bigger the drawthrough the outlet the quicker it will shut off. If it shuts off and I turn it off and back on it will do it again with about the same time frame. When I had my PC which has a 750w PS plugged into it it will shut off about once a day. If I have something with a small amount of draw it will shut off anywhere from 2½ to 4 days. Can't figure out what it is yet and haven't been able to find any clues searching the net yet either. Oh well. It's not hooked up now so that a project for another day.
 

paulears

Member
Joined
Oct 14, 2015
Messages
490
Location
Lowestoft - UK
Could it be due to you putting the PC under a heavy workload, requiring it to draw more wattage from your power supply, making it work harder, along with your CPU and GPU? Also, under load, many PC will start to spin their CPU and GPU fans faster in order to keep the temperature down, so could be getting increased EMI from those fans as well.
The content of a screen doesn’t change the current requirements does it? I’m not sure that fans generate RFI as they’re DC devices but in my case, it’s to do I assume with the monitor or possibly the video cards, I don’t know yet.
 
Top