Yet Another !&*%$! Noise Source

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.

2 thoughts on “Yet Another !&*%$! Noise Source

  1. I have found some laptops which generate noise on the FRS band enough to break squelch if the receiver is in the same room. But I have a new issue which eclipses everything now:

    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 quickly 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 still cannot receive several AM stations which I could copy reliably prior to 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.

  2. Pingback: More adventures in filtering the power supply for an AFE-822 SDR |

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