I have attached a video of some RFI I have on 20 meters. You can see the RFI in several locations across the band. But when I transmit, it goes away for about 30 seconds and then returns. I live in a rural area, so I thought it might have been an electric fence charger, but it does not sound like one, and they would not be smart enough to stop when I transmit. Also, along with all the usual suspects in a modern home (switching power supplies, LED lights, laptops, desktops, TV, etc), I have a smart meter, cable internet, and a dish satellite system for TV. I think it is local, as I can switch my tuner to Ant 2 and pick the RFI (weak) with a short piece of wire. 

Does anyone have an idea where to look?  I plan to set up my SDR and laptop as a portable receiver so I can sniff around and attempt to locate the source. But thought maybe someone out there has already identified this.

Thanks
--
Dennis
KA6FUB

Attachments:

• RFI 28 March 2023.mp4

Hi Dennis,

Interesting.  I can’t figure out why the RFI would pause after you transmit, whereas the other signals don’t.  Do you see the RFI at other frequencies outside of the 20 meter band?  If you tune your SDR receiver to a different frequency where the RFI is present, but transmit a test signal of 20 meters, does the RFI also disappear at the other frequency?  Alternately, if you leave the SDR tuned to 20 meters but move your transmitter to 40 meters or 15 meters and transmit a test signal there, does the RFI on 20 meters disappear momentarily?

As to the source, I agree it doesn’t sound like an electric fence charger.  Do you have solar panels on your house or nearby?  I’d expect to see solar panel RFI at lower frequencies too, perhaps more in the 200 to 500 kHz range.  But why transmitting would pause any solar RFI is beyond me.   Is the RFI present at all times of the day or night?  If it disappears at night, you might be able to rule out solar panels.  I see the recording was made at 23:10 UTC, so it would be mid/late-afternoon at your QTH in Oregon.  Do you have a whole-house generator?  The battery charger in my whole house generator throws out RFI at multiple frequencies in the HF spectrum, but I can’t explain why transmitting might cause that battery topper to switch off momentarily.

Does the tempo of the “beats” ever change through time, say over an hour or so?  Does it ever slow down or speed up at different times of the day? The answer to that doesn’t identify the source, but might help others come up with ideas.

The first thing I would try is to unplug potential sources like the cable modem, any WiFi routers, dish satellite system, etc. one at a time and check for the RFI.  You mention a tuner – does it use a power supply for its memory, backlight, etc.?  If so, try unplugging that.

I’m looking forward to ideas from others.  Keep us posted on what you find out.  Good luck and 73.

Ken -- WBØOCV

I have attached a video of some RFI I have on 20 meters. You can see the RFI in several locations across the band. But when I transmit, it goes away for about 30 seconds and then returns. I live in a rural area, so I thought it might have been an electric fence charger, but it does not sound like one, and they would not be smart enough to stop when I transmit. Also, along with all the usual suspects in a modern home (switching power supplies, LED lights, laptops, desktops, TV, etc), I have a smart meter, cable internet, and a dish satellite system for TV. I think it is local, as I can switch my tuner to Ant 2 and pick the RFI (weak) with a short piece of wire. 

Does anyone have an idea where to look?  I plan to set up my SDR and laptop as a portable receiver so I can sniff around and attempt to locate the source. But thought maybe someone out there has already identified this.

Thanks
--
Dennis
KA6FUB

Attachments:

• RFI 28 March 2023.mp4

It is possible that your RF is stopping an RF sensor or something similar from transmitting if some form of crude CSMA/CD is in use.

See here:

https://www.tutorialspoint.com/csma-with-collision-detection-csma-cd

The pulses sound like what you can get from cheap and nasty sensors used with some thermometers, however I have never heard this on 14MHz, usually they are at 433MHz here in Europe. Not sure about the USA. These things may have zero filtering. It’s a good idea to look around with an SDR. I also expect this to be very local.

Regards

Conrad PA5Y

Hi Dennis,

Interesting.  I can’t figure out why the RFI would pause after you transmit, whereas the other signals don’t.  Do you see the RFI at other frequencies outside of the 20 meter band?  If you tune your SDR receiver to a different frequency where the RFI is present, but transmit a test signal of 20 meters, does the RFI also disappear at the other frequency?  Alternately, if you leave the SDR tuned to 20 meters but move your transmitter to 40 meters or 15 meters and transmit a test signal there, does the RFI on 20 meters disappear momentarily?

As to the source, I agree it doesn’t sound like an electric fence charger.  Do you have solar panels on your house or nearby?  I’d expect to see solar panel RFI at lower frequencies too, perhaps more in the 200 to 500 kHz range.  But why transmitting would pause any solar RFI is beyond me.   Is the RFI present at all times of the day or night?  If it disappears at night, you might be able to rule out solar panels.  I see the recording was made at 23:10 UTC, so it would be mid/late-afternoon at your QTH in Oregon.  Do you have a whole-house generator?  The battery charger in my whole house generator throws out RFI at multiple frequencies in the HF spectrum, but I can’t explain why transmitting might cause that battery topper to switch off momentarily.

Does the tempo of the “beats” ever change through time, say over an hour or so?  Does it ever slow down or speed up at different times of the day? The answer to that doesn’t identify the source, but might help others come up with ideas.

The first thing I would try is to unplug potential sources like the cable modem, any WiFi routers, dish satellite system, etc. one at a time and check for the RFI.  You mention a tuner – does it use a power supply for its memory, backlight, etc.?  If so, try unplugging that.

I’m looking forward to ideas from others.  Keep us posted on what you find out.  Good luck and 73.

Ken -- WBØOCV

I have attached a video of some RFI I have on 20 meters. You can see the RFI in several locations across the band. But when I transmit, it goes away for about 30 seconds and then returns. I live in a rural area, so I thought it might have been an electric fence charger, but it does not sound like one, and they would not be smart enough to stop when I transmit. Also, along with all the usual suspects in a modern home (switching power supplies, LED lights, laptops, desktops, TV, etc), I have a smart meter, cable internet, and a dish satellite system for TV. I think it is local, as I can switch my tuner to Ant 2 and pick the RFI (weak) with a short piece of wire. 

Does anyone have an idea where to look?  I plan to set up my SDR and laptop as a portable receiver so I can sniff around and attempt to locate the source. But thought maybe someone out there has already identified this.

Thanks
--
Dennis
KA6FUB

Attachments:

• RFI 28 March 2023.mp4

It is possible that your RF is stopping an RF sensor or something similar from transmitting if some form of crude CSMA/CD is in use.

See here:

https://www.tutorialspoint.com/csma-with-collision-detection-csma-cd

The pulses sound like what you can get from cheap and nasty sensors used with some thermometers, however I have never heard this on 14MHz, usually they are at 433MHz here in Europe. Not sure about the USA. These things may have zero filtering. It’s a good idea to look around with an SDR. I also expect this to be very local.

Regards

Conrad PA5Y

Interesting comment, Conrad.  There are some consumer devices, such as electric toothbrushes (and perhaps others – razors, ???), which use near-field communication (NFC) at ~13.56 MHz.  Why an electric toothbrush needs to “communicate” is beyond me, but I guess it has something to do with ‘identifying’ the proper brush head attached.  If I cycle the power on my Philip Sonicare toothbrush, or place it on or off the charging cradle, it will emit a signal at 13.56 MHz, usually of short duration of about 30 seconds or so.  Usually I can’t detect it if the antenna is attached to my SDR, but if I disconnect the antenna and attach a short wire to the SDR input and place the toothbrush close to is, I can see the RF packets.  The ‘pings’ from my toothbrush are more rapid than those in Dennis’ video, and the packet is less that 1.5 kHz from edge to edge, much narrower than Dennis’ example.
I wonder if collision detection might be used in such devices.  That frequency range is near the 20 meter amateur band, so might be a candidate for the RFI.  If a charging cradle is using NFC to detect a potential object to be charged, perhaps Dennis has a defective charging cradle that is “searching” for a device and throwing out an RF signal. It might be worth checking such devices, Dennis.
Good luck and 73.
Ken -- WBØOCV
*From: *Conrad, PA5Y <mailto:g0ruz@...>
*Sent: *Wednesday, March 29, 2023 08:52 AM
*To: *main@SDR-Radio.groups.io <mailto:main@SDR-Radio.groups.io>
*Subject: *Re: [SDR-Radio] Help Identify RFI
It is possible that your RF is stopping an RF sensor or something similar from transmitting if some form of crude CSMA/CD is in use.
See here:
https://www.tutorialspoint.com/csma-with-collision-detection-csma-cd <https://www.tutorialspoint.com/csma-with-collision-detection-csma-cd>
The pulses sound like what you can get from cheap and nasty sensors used with some thermometers, however I have never heard this on 14MHz, usually they are at 433MHz here in Europe. Not sure about the USA. These things may have zero filtering. It’s a good idea to look around with an SDR. I also expect this to be very local.
Regards
Conrad PA5Y

I used the entire 12 Mhz of bandwidth on my RSP Pro and discovered this RFI down to 3 Mhz. And if I transmitted in different bands, the RFI in that band disappeared for 30 seconds. I also see a carrier scanning through the entire HF band every 10 minutes or so.

I hoped someone else had seen this and could point me to the possible source. So this afternoon, when it warms up, I will take my laptop and SDR on a hunting expedition around the property.

Will post here what I find.
--
Dennis
KA6FUB

I used the entire 12 Mhz of bandwidth on my RSP Pro and discovered this RFI down to 3 Mhz. And if I transmitted in different bands, the RFI in that band disappeared for 30 seconds. I also see a carrier scanning through the entire HF band every 10 minutes or so.

I hoped someone else had seen this and could point me to the possible source. So this afternoon, when it warms up, I will take my laptop and SDR on a hunting expedition around the property.

Will post here what I find.
--
Dennis
KA6FUB

Found the problem. It was a poor connection to the USB shield/shell at the Pi. I have shielded USB cables and have ensured that the shield connects to the shell of the connectors.
I disconnected the USB keyboard cable to see if that affected the RFI, and it did not. I re-connected the keyboard, and the RFI was gone. I messed with the keyboard connector a bit and then realized that I was moving the USB cable that goes to the dongle. So messing with it, I discovered that the shell of the connector was not making a good connection to the shell of the jack.
--
Dennis
KA6FUB