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I'm very new to shortwave listening and just got to grips with my RTL SDR HF dongle. Last night while on the 20m band, there were signals exactly every 50kHz, starting exactly at 14.000MHz, then at 14.050 MHz, 14.100 Mhz and so on. Google said they may be my power supply. Today I wanted to troubleshoot them but they are mostly gone, making me even more curious to what they could be as I have exactly the same electrical equipment on today.

RTL-SDR Waterfall showing signals every 50 kHz

Here's a close up of the one that was at 14.200 MHz

enter image description here

The SDR is connected to a very simple wire dipole with a 1:1 balun. One end of the antenna is attached to the top of my two storey house but the other end is much lower down, attached to a metal gate (but via insulated dog bone connector).

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    $\begingroup$ Last night... might suggest a neighbor's LED lights, or perhaps a power-line dimmer, or a motor speed-control triac or SCR. Hard to troubleshoot until the "signal" returns. $\endgroup$
    – glen_geek
    Commented Dec 27, 2021 at 17:12
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    $\begingroup$ 50 Hz is line voltage. Commonly will cause harmonics at every 50 Hz frequency above that, although each individual harmonic will be at potentially different levels. Florescent lights, noisy power supplies, etc. $\endgroup$
    – Steve
    Commented Dec 28, 2021 at 16:52
  • $\begingroup$ Do you have a regular analogue SSB HF radio? Connect the same antenna to it and check whether you hear these signals. My bet is that they're generated inside the SDR by other strong signals - perhaps AM radio, or FM, TV or cellular phones. $\endgroup$
    – tomnexus
    Commented Dec 29, 2021 at 15:53
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    $\begingroup$ Every 50.000kHz suggests an impressively accurately designed source of interference! Be interesting to know what brand of washing machine, LED bulb, or commonplace interference source you find... $\endgroup$
    – user_1818839
    Commented Dec 29, 2021 at 20:45
  • $\begingroup$ ![enter image description here](i.sstatic.net/XBzGn.jpg) ![enter image description here](i.sstatic.net/PNT4A.jpg) I'm so glad I decided to check that! $\endgroup$
    – Randell Lamontagne
    Commented Sep 5, 2022 at 7:05

7 Answers 7

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Those equally spaced lines in the waterfall are very likely from EMI/RFI noise generated by modern electronics, often harmonics and/or intermodulation coming from DC-to-DC power converters. Could be something inside an LED light or lightbulb, USB charger, wall-wart switching power supply, computer peripheral or network hub, video monitor, solar panel, or almost any modern appliance in either your house or a neighboring house or building. If you shut off the main circuit breaker to your house and those lines go away, the noise source is likely in your house. If not, it could be something radiated from a neighboring building or power pole. If it is in your house, you could go room-by-room, unplugging things until you find (one of) the sources.

If the lines went away, it could be someone unplugged something or turned something off.

This has become a common problem the last few decades in any urban or suburban locale where modern electronic devices, appliances, or lights are in use. Much of that hash between the equally spaced lines is likely more of the same, just a mashed up mix at lower levels.

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    $\begingroup$ Oh, yes. And the most peculiar sources of spurious emissions, they are. Lottery machines, cut CATV lines, and cheap light bulbs. You know who is interested in interference? The folks who paid billions for bandwidth--the cellular operators--and want a very low noise floor. Adding a small fraction of a watt to a transmission, just to overcome interference,--well multiply that by the millions of calls--and you have a reason to chase interference. Turn the power off to your house. Walk around with a battery powered receiver or some other piece of kit. Then you know you're clean. $\endgroup$
    – Robert Hadow
    Commented Dec 28, 2021 at 3:38
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I notice you said 50 KILOhertz, not 50 hertz. Big difference, folks!

You're picking up interference from some sort of electronic device that has a component producing a 50 kilohertz wave. Since this appears to be dead-on accurate down to a kilohertz or less, it's probably controlled by a quartz crystal. Any time a signal is produced at some frequency, there is almost always other signals produced at integer multiples of that frequency, called harmonics. At 14.050 MHz, you're seeing the "280th harmonic" of 50 KHz.

To find this, watch the display as you go around the house unplugging literally everything. In my case, it was the fancy new washing machine we bought! Also take the batteries out of everything. The 280th harmonic of something is going to be really weak, and you're picking it up full-scale, so it's probably something really close by.

Welcome to radio, by the way! Glad to have you.

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  • $\begingroup$ I had to recheck but yes, it does seem to be every 50 kHz and NOT 50 Hz. $\endgroup$
    – rcx935
    Commented Dec 29, 2021 at 9:56
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I had the same problem......discovered it was my florescent house lights in which I have led replacement tubes.

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At first I'd have said it's Xmas lights or a SMPSU, but then the 50Hz part got me thinking and remembered that it's more likely to be Ethernet over Power line device, they are also known as PLT's. These create RF noise of all types all over the radio spectrum either all the way through constantly, or in little blocks that come and go. Some have radio detection and turn part of the spectrum off temporarily if they hear strong RF in that part. This is no good for radio hams and even less so for SWLer's because they cannot force them to switch off at all. They are legal because they are considered to be modems and therefore have exceptions on noise pollution limits other types of devices are required to meet. The manufacturers claim the signal stops at the home electricity meter, but this is completely untrue as you can hear the signals yourself.

If this noise goes away then it probably is because it's from Xmas lights or an Xmas related switch mode power supply if however it stays the odds are it's a PLT device and you will never get rid of the noise until the source has been located and helped to switch to ethernet cable instead.

If you are really lucky and it is confirmed to be PLT, you could see if a few short high powered bursts causes the noise to stop for a while. And even better if you do this enough maybe the owners will reconsider using these nasty devices. Good luck.

Side thought have you tried using a hand held radio perhaps a MW or LW AM broadcast radio to DF the source?

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    $\begingroup$ 50 kHz, not 50 Hz $\endgroup$
    – pipe
    Commented Dec 28, 2021 at 22:02
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Mine was from my ethernet router in my radio room. It didn't show up on lower bands, but started across 20 meters, and on harmonics. Unplugging the router made the problem, but I couldn't operate 20 meters as long S the router was activated.

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Vizio[![enter image description here][1]][1] inexpensive Chinese TV First of all I sincerely apologize for the terrible picture quality. Had my laptop camera pointed my radio and used the screen recorder on Android well viewing remote desktop. I ran around the whole house unplugging the everything. Finally figured out it was the cheap Vizio TV. When I turned it on it at the bars all the way across my waterfall the last photo is me turning it off.

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  • $\begingroup$ As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center. $\endgroup$
    – Community Bot
    Commented Sep 8, 2022 at 6:01
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Try disconnecting your antenna to see if its entering the radio via that path.

Ethernet interference (at least 10/100) has a different profile I've covered here

Hunting RFI with bars every 61 khz

And gigabit is a bit more white-noise like.

Try disconnecting the antenna when the rfi is again present to determine which path the rfi is taking to enter the radio, and troubleshoot accordingly.

I agree with other posters that its likely an electronic device that was on then off which is why it went away.

If entering from the antenna it may be tricky to find as rfi can be received by a HF antenna from quite far away given its size & height. Finding the right house, or utility, the right device, obtaining permission to rectify the issue, or logging a job to fix, and if anything can even be done about it, start to become long shots. I wish you luck in finding the source and if you do find the cause, adding an answer to this post would help others too.

Sometimes using an antenna with opposite polarisation (ie if horizontal then vertical, and vice-versa) might help if its out of your control. Not a guarantee, but might eliminate or lessen its intensity.

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