The Dreaded Wall Wart


It seems that the ARRL has made it official ... well, maybe not, but at least Ed Hare, W1RFI has. In a recent interview on the HamRadioNow webcast, Hare said that he believed that switching-mode power supplies are a more common source of QRN than noisy power lines ... and I believe him. I have heard countless horror stories of amateurs having to go QRT for good (at least on HF) because of issues with neighbourhood switching supplies. It's one thing to be able to hunt these things down and remediate the problem within your own home but when it comes to the whole neighbourhood, it's an awfully large challenge. And it's not as if there's just the odd one around, here and there ... they are everywhere.

In Ed's own words:

 “The old days of those iron transformers are gone,” Hare said. “Every single one of these is a switcher. We’re also seeing noise from pulse-width control motors.” Hare said the big culprits are “little wall warts,” not switching supplies designed to power Amateur Radio gear. “Every TV you own has a built-in switcher, almost every device has a wall-wart, and a lot of these are imported, not necessarily meeting the FCC rules, so we’re seeing more reports involving those.”

I've never personally had a problem with a wall wart, other than a cheap charger for my I-Pad, but that's not to say I haven't run into switchers. The charger emitted a low-level hash that I could hear only on a very quiet 6m band, not much of a real problem considering that I could unplug it at any time. A couple of problems here in the neighbourhood were eventually traced to the poorly designed or faulty switchers inside some CFL bulbs. These were emitting signals via the powerlines and being picked up by my antennas almost two blocks away. This was a problem only on LF however, where the powerlines make pretty efficient antennas.

Hare went on to say that some of the new LED-type lightbulbs have proven to be noisy as well. Not hard to understand when each one has its own low voltage switching power supply. What is hard to understand is why these device are even allowed on the market without having to undergo some type of noise-testing for approval. Another 'growing' threat are the lights used by neighbourhood grow-ops, legal or otherwise.

Hare also indicated that the ARRL lab can work with manufacturers to correct problems but that they need to know specific model numbers and information about the problems you are experiencing with the device.

Apparently, according to Hare, many issues can be resolved without involving enforcement from the FCC, the last step, should issues not be resolved by other methods.

You may be able to help by sending the needed information to the ARRL Laboratory for this and other types of RFI. Both Ed Hare and ARRL EMC Specialist Mike Gruber, should be contacted if you can supply information or have an unresolved problem.

The excellent 11-minute interview (Episode 196 'W1RFI's Tall Tales from the ARRL Lab') can be watched here, with thanks to HamRadioNow TV and to Gary Pearce, KN4AQ of HamRadioNow.
Steve McDonald, VE7SL, is a regular contributor to AmateurRadio.com and writes from British Columbia, Canada. Contact him at [email protected].

6 Responses to “The Dreaded Wall Wart”

  • Harry K7ZOV:

    I had different problem with a switching wall wart.. Cable-One supplies all our cable needs. They like everyone else has gone digital and so they supply two free converters. Naturally with a small switching supply wall wart. When even I fired up my KPA500 and started talking the unit would reset. Mostly on 40-15 meter. 10 meters no problem. Then I found, depending on the band, that different power levels would mean being on the air would kill TV for the XYL..

    So Cable-One came out twice and the second time it was a guy with real RF background. We determined it was NOT the box, but the switching supply and he changed to a different brand and not more problems. It seemed that instead of be a RFI device it was a RX instead.

    Two other cased popped up in the area. Another Ham and one guy who had a wall light dimmer. He would dim the lights and enough crap from the dimmer that was on the power line would reset the cable box. They changed his PS and the problem went away.

    So we have a new chapter of possible future problems. Not for radiation of RF but being a RX and locking up the PS…

    73 Harry K7ZOV

  • Cliff KU4GW:

    Got a new noise issue that just appeared! I had AT&T U-verse Internet connected here this past Friday and this new internet uses packets instead of a asynchronous connection with a varying speed. The new type holds a more steady speed, but now I have to run the notch filter on my Yaesu FT-1000MP Mark V all the time on 75 meters or I can hear the U-verse packets. I can live with it so long as the notch filter keeps doing the fine job that it is, but thought I’d pass the info on that it does that. Thankfully it doesn’t affect the 80 meter CW portion of the band or any other band besides the phone portion of 75 meters which the notch completely eliminates! As far as wall warts I’ve been lucky! I did have a issue a while back with a Black & Decker Firestorm Rapid Charger for my 18 volt cordless drill that took me 2 days to find, but it only makes a ticking noise when a battery is sitting in the charger. Very 73!

  • Steve VE7SL:

    ….and the sad thing is, this could probably be prevented at manufacture with the addition of a couple of small components.

  • Gene, W5DOR:

    As a retired elec engineer I’ve been quite aware of the problems with noise producing switchers. Luckily, I had found a 13.8VDC, 30A linear power supply for my 100W transceiver but use wall warts for most of my home-brew rigs except in the field where I use batteries. I even have a home-brew line filter for my rigs in the shack made of 30A inline filters and common-mode filters. In my home-brew receiver circuits I pay close attention to the supply lead decoupling and try to use some of the new “ultra low-noise” regulator devices.

    BTW, I still have the pic of your “6L6 Tri-Tet-Ten” rig that you sent me. I still remember that day when I found 10m CW dead until I came across a strong “chirpy” CW signal. I had a FB QSO with you and your 4w 6L6 rig.

  • peter kg5wy:

    Cliff, I have a ft5000 and a Uverse box right next to it.
    I am not sure I am receiving and noise or packets. How could I tell?

  • Steve VE7SL:

    Nice to hear from you Gene! The Tri-Tet-Ten is still on the operating bench but I fear that its glory-days on 10m may soon be over forever. From what the solar guys tell us, future cycles don’t look promising. I’ve had a ball with the little transmitter, working WAC a couple of times and several dozen Europeans. My main goal was just to work EU with a single 6L6 xtal oscillator using a 40m xtal and I was amazed at the results. When 10m is good, there is nothing quite like it. Hopefully we can have another QSO in the fall if the sun stays busy enough for 10m! 73

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