Chris tracks down sources of radio noise


Many thanks to SWLing Post contributor, Chris Smolinski, who shares this guest post from his blog,

Yet Another !&*%$! Noise Source

by Chris Smolinski

The past few days, I have noticed higher than usual noise levels, generally on the lower frequencies, and particularly on the longwave band, including the 285-325 kHz DGPS band, where I run nightly SDR recordings, to later process the data and decode and detect DX DGPS stations using my Amalgamated DGPS app.

Thinking back to what new electronics devices have been added to the house, two came to mind, a new cable modem, and a new ethernet switch. The switch is up here in the shack, so it seemed to be a likely candidate. The switch is a D-Link DES-1008E 8-Port 10/100 Unmanaged Desktop Switch. It uses a mini USB port for power, using either the included AC adapter, or power from a USB port. When I installed it, I decided to not use the AC adapter, but rather a USB port on my UPS, figuring it was better to not add yet another potentially noisy switching power supply to the mix.

The test was easy, I just unplugged the power to the switch. Sure enough, the noise vanished. Great, the switch is a RFI generator. Or is it? As another test, I plugged it into a port on a USB hub. No noise. Hmm… so it seems that the noise is indeed from the USB port on the UPS. I did not notice any increase in the noise floor when I got the UPS a few months ago, but It’s something I should look into again, just to be sure. The UPS is a CyberPower CP1350PFCLCD.

Here’s a waterfall from the SDR, showing the DGPS band, 280-330 kHz. You can see where I changed the power to the switch from the UPS USB port to the USB hub, the bottom part of the waterfall is when the switch was still powered by the UPS (click to enlarge it):


I still have a noise source just above 305 kHz to hunt down.


I decided to see what I could do to improve things, and reduce the noise floor.

Here is the baseline, after no longer powering the switch from the UPS:

First, I relocated the AFE822 away from the computer and rats nest of assorted cables behind it, powered from an HTC USB charger:

The squiggly noise around 305 kHz vanished!

I then switched to an Apple USB charger / power supply, as their products tend to be a bit better made:

Another improvement, the overall noise floor is a bit less now.

But can we do better? I then switched to an older USB hub for power to the AFE822, that I thought might be better filtered:

I then changed to a linear supply plugged directly into the AFE822. I don’t notice any obvious improvement? Maybe it even looks like a little more noise? Difficult to tell. You can see a DGPS station popped up on 304 kHz while I was switching things around, between the last two tests, it was likely Mequon, WI.


Thank you for sharing this, Chris! I find a wideband spectrum/waterfall to be such a useful tool for tracking down sources of noise. Not only can you “see” the noise, but you can measure its bandwidth and identify what portions of the dial it affects.

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12 thoughts on “Chris tracks down sources of radio noise

  1. DL4NO

    Thank you for this extensive link list! I forwarded it here in Germany.

    You support my opinion (see my comment above) that PLC and other “wire-bound” RF sources will expand up to the FM band as this allows them either more bandwidth or cheaper prducts (with less RF suppression circuitry).

    In Mannheim, a larger city near the French border, an ISP was allowed to use PLC to distribute internet access to homes. In the respective suburb and around it no MW or SW reception is possible. Even lawsuits could not stop this dangerous nonsense.


    PLC article index

    Smart Meter article index

    Most relevant points:

    Smart meters radiate from two noise sources:
    • power line communication signals (PLC)
    • transients from switched power supplies, transmitters, etc.

    Both can enter the house from the neighbor’s meter as well. The pulses create broad spectrum harmonic waves. Meters communicate by adding their individual frequency to the power lines. Some household meters may act as a relay station. A relay meter could be transmitting continuously.

    PLC systems are not considered wireless systems but the wires will always radiate. Utilities like to say that this isn’t true, and the FCC apparently believed them. However, the PLC antenna effect is now a well-documented fact.

    FCC found power line communication exceeds radiation limits and tried to cover it up:

    The FCC released the reports during the lawsuit, but blanked out important information. It took a year and a FOIA request to get it released. It is disturbing that 3 of the 7 systems had measured emissions at or above FCC radiation limits, especially since the FCC limits are much higher than those in Europe and Japan.

    Japanese government study shows radio broadcasts completely masked by PLC noise

    The miles of electrical wires in a neighborhood can act as a very large antenna. Radio amateurs found interference 1100 meters from power lines.

    Few PLC systems go above 30 MHz, due to increasing problems with line losses. The upper limit is probably 80 MHz, as FM radio reception could then be impacted.

    The interference will stretch across the whole of the spectrum and will be broadband in nature. Some systems may use low-frequency carriers such that a continuous audible tone is present across the frequency range.

    There will also be a wide range of harmonics generated from the basic pulse transients. The power supply inside digital utility meters is a common source of dirty electricity. The signals will enter any building connected to the grid, it is not really possible to block them.

    Major US power supplier downplays widespread interference reports

    Powerline networks are also wireless networks!

    NIST admits that PLC signals can travel between homes

    Stealth smart meters: Analog meters with hidden transmitters

    PLT and broadcasting – can they co-exist?

    The European utility E.ON has developed a line filter which dampens power line signals in the kilohertz range. It is installed next to the electric meter on customer residences.

    The filter would be installed without cost to the ratepayer. Another option was to let the ratepayer keep the mechanical meter and simply send in a postcard once a month with the numbers.

    Eurelectric convention delegates say smart meters not needed

    Video demonstrations:

    Power lines turned into giant antennas (FCC survey)

    In house / portable radio

  3. mik12

    I have noticed that digital AM tuners are often affected by smart meter RFI more than analog tuners. Operating the receiver on batteries can reduce the noise but does not always eliminate it. This is obviously not an acceptable solution for those who just purchased a new desktop radio which uses an AC to DC power supply, but it can be used to demonstrate how reception is being affected by wirebound RFI.

  4. XR234

    > Wire-bound RFI often is very difficult to track down: It runs along any cables and the field strength can be highest far away from the source.

    Great point, DL4NO. I have an interesting experience to relate about that:

    I frequently listen to several high power distant stations and low power local stations on the AM broadcast band. After my neighbors “smart” electric meter was installed, I suddenly could not receive these stations due to interference. I soon discovered that this interference also completely destroyed my shortwave reception. I conducted a survey by carrying a portable AM receiver towards the smart meter and positively confirmed that the meter is the source of interference. At close range the digital pulses completely overwhelmed audio signals on many frequencies across ALL broadcast bands. This RF leakage was so intense that nearby underground telephone lines could be followed just by walking along with the receiver in hand, listening for digital noise. The same noise appeared at lower RF power levels near some electrical outlets and the main AC panel within my home. Strong interference was also present on the lower end of the AM broadcast band while driving past the neighbors house.

    I wondered if the meter could have been improperly installed, since other nearby smart meters do not radiate the same high levels of RF noise. After a friendly complaint, it appears that the power company might have made some adjustment which reduced the RF radiation. For all I know, this could have been addressed through a remote firmware update rather than some electrical modification. Some of the stronger shortwave stations can now be heard again, but the smart meter noise is still audible. I also cannot receive several AM stations which I could copy reliably before the smart meter installation, particularly at night. On some frequencies this interference presents as clearly audible digital pulsations, but on many other frequencies it presents as a hissing sound which is almost indistinguishable from ordinary background noise. In the latter case the average listener might not be aware that a nearby smart meter is the cause of his inability to receive a radio broadcast.

    While researching this I found some broadcast engineers who said that many smart meters are actually violating the legal RF power limits on unlicensed transmitters, but these violations can only be detected on a peak reading signal meter (not RMS) because the digital pulses are so brief. Anyone can see that it is not feasible to audit millions of smart meters on a regular basis for such violations. If a pirate broadcaster or radio jammer stole a million listeners from a licensed broadcaster, no doubt they would howl in protest. But the same broadcasters seem oblivious to the loss of audience due to increased background noise from smart meters!

    Smart meters could be using two different networking methods here: peer-to-peer wireless and RF over power lines. It seems to me like noise is leaking from one side to the other, but is not clear which direction. I understand why the power company would like to possess the ability to turn electric service on & off by remote control, but this is absolute madness when a hacker or virus could use the same network to shut down entire cities at once. Even if this network could be secured, the constant and unnecessary transmission of excess digital data should not be allowed if it harms the broadcasting industry.

    Now I am seeing other posts which report that millions of good working power meters are being replaced simply for the sake of collecting real time data from the customer, and this is being financed with rate increases or government subsidies. There is also a total news blackout on this subject in the establishment media. And the same politicians who are blaming the russians for the democrats defeat are trying to hide the national security implications of the smart meter threat! The potential for politicians and regulators to profit immensely through kickbacks by spending the taxpayers money on unnecessary meter replacements would certainly explain WHY they are racing to deploy smart meters with absolutely ZERO concern for protecting critical infrastructure and preventing interference to radio services. Only a fool or a crook would be so reckless and irresponsible.

    1. DL4NO

      Welcome to the club 🙁

      Many of these smart meters use “power line” technology for their communications channels. This technology will kill most wireless communication below 68 MHz or so over time.

      Here in Europe we theoretically have quite strict EMC (electromagnetic complience) laws. There even is a standard for powerline technoloogy equipment but this standard defines EMC testing only without any data traffic going through. As soon as you transfer any data this equipment will most certainly exceed the generally accepted RFI (radio frequency interference) levels. As specialized industry standards supersede general industry standards, powerline equipment according to these specialized standard may be distributed.

      To make it even worse: The law about EMC violations has just been revised here in Germany. In the future the BNetzA (Bundesnetzanstalt, if you can pronounce it) *may* track down EMC problems. But it only *must* do so if security services are involved.

      This is how I came to “below 68 MHz”: Besides some military communication hardly any security service uses frequencies below 68 MHz anymore. Broadcasting starts at 87,5 MHz (FM) with DAB+ in the 170-220 MHz range. With the shut down of analog systems hardly anything will use frequencies below 170 MHz. Security services are mostly moving to the 400 MHz range.

      All this opens more bandwidth for powerline services :-((

  5. Pingback: Chris tracks down sources of radio noise –

  6. DL4NO

    Wire-bound RFI often is very difficult to track down: It runs along any cables and the field strength can be highest far away from the source. A tiny USB power supply can provide quite some noise!

    Chris shows how to do it: Remember what you have changed recently and eliminate the sources by switching them off. It even helps if your receiver can be battery powered.

    In my cellar I have some 30 circuit breakers. Enough possibilities to locate the source…

  7. rtc

    Thank you for this article.
    Had/have the same problem here…it was the UPS and the router which were
    turned off.
    The other thing (which can’t be turned off) is the transfer switch for the
    Possible fixes (neither of these have come in yet) are
    ($70 USD delivered)
    (scroll down for the RF Isolator,$38.00 USD delivered))
    The RFI is not being picked up on the PK Loop/Sony 7600,just on the
    longwire coax which runs thru the basement across from the transfer switch.
    It’s a long shot but we’ll see.
    BTW if you use an end fed longwire,this is highly recommended:
    Around $50 USD delivered,an UnUn,and worth every cent.


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