It's been a year or two since I listend to AM Radio, and in that time theres a new Roku box and linksys router. Well, I couldn't hear anything on the AM band when I checked a week ago. So the quest was to find the culprits. Its these SMPS wall warts, they literly wipe out the entire AM band, and also some chinese LED lights( 15w equiv Grimaldi's ). Tossing the led lights are easy, the wall warts not so. I found the old DSL modem transformer wall wart and that is quiet. Perusing the Innernet, I see some mention Apple supplies and the Powerstream SMPS supplies are quiet too, any one here with experiance with them?
Same problem here, except we have flourescent lights with solid-state ballasts, and the line noise is something to behold. The noise blankets everything up to about 10MHz. The only solution here is to take the radio
100 yards out in the middle of a field. There is still a lot of noise, but at least you can pick up some stations.
I bought a very nice synthesized receiver to listen to the ham and broadcast bands. To my dismay, I found that most of the shortwave stations have shut down, since they have switched to the internet. About the only ones still operating were the religious nuts trying to get donations. The ham bands were down a lot also. I guess the old guys have died off, and amateur radio doesn't have the same appeal as google.
Electronics seems to be following the same route as the vacuum tube. But there are very active local clubs into Arduinos and robotics, so there is some hope for the future.
Short wave had its day. It was a hard way to do a fraction of what the net does now. AM ie MW/LW likewise really. The only thing of interest on SW was the nutty & the politically iffy stations, now we got 1000s times as many online.
This is also the reason why nobody cares about the interference from wall warts. The AM (HF) bands are no longer used by the public.
Besides, there is interference from almost any technology in use today, not only switched-mode power supplies. There is ethernet over powerline, DSL, wireless charging, RFID, and the list goes on and on.
It is better to throw the towel and give up on receiving AM.
Most likely DSL supply was an old style iron core transformer operating on 50 or 60 Hz.
These iron core wall warts are heavier than the SMPS wall warts, so a quick check is easy to do,
Just replace the noisy SMPS with an iron core wall wart. Check the output voltage and is it AC or DC and get a similar iron core model. It doesn't have to be a wall wart, one with a mains core works OK.
The same problem all over the world in urban areas. For this reason, some hams use a remote controlled receiver at their (quiet) summer cottage and transfer the received audio over the internet to their apartment. Some also have remote controlled transmitters at the summer cottage.
An other alternative is to use some shared wide band receivers to tune in individual stations over the net. Take a look at
There are still some news and/or propaganda stations.
The number of CW or SSB speech transmissions has dropped drastically. A large group has moved to various digital modes. Check the waterfall display of a ham band to see the number of digital transmissions.
You are welcome to stick your head in the sand! I am a radio amateur myself, but fortunately only active on VHF/UHF/SHF. The HF amateurs are complaining all the time about those technologies and trying to get them abolished so they can continue their hobby, but realistically it is just a very small group compared to users of modern technology.
Well if the ferrite didn't work you could try a shield. I made this power supply with DC-DC converters. Nice layout and ground planes, but still switching noise. I put copper tape hats on the converters and that knocked it down.
FWIW, ferrites rarely do more than 3-6dB of attenuation. A long stack of them, maybe over 10dB. The reason is, if there's no shunting impedance (to ground, or, more generally, to the other cable coming out of the box), it's an impedance divider against the capacitance-to-space of the cables in question.
It's probably even more basic than shielding: you need to start with a shunting impedance in the first place. This is usually a 1nF Y1 ceramic cap between rectified mains and secondary grounds.
A lot of USB charger style warts have even less capacitance. It's not clear to me if they have a shielded transformer (unlikely, but possible; I need to take one apart some time), or if they really just don't care (there's very little radiation from a wall wart, if there's no charging cable and load plugged in ;-) ). They don't usually have a CMC, or just a small one and no other Y caps if they do. (Again, not good for much, without a shunting impedance to help out.)
So, after adding a few caps and chokes: your next goal is shielding, surrounding the PSU core with chokes, and shunting all inputs and outputs with caps to the shield. (Shield should also be earthed, because leakage current and safety.)
There is a lot of digital stuff around 14.070. PSK and other varied modes. Of course the solar cycle is poor right now. Evening seems best. I like to rx the NOAA HF WEFAX stuff but they are having some problem with sync jumping making pix pretty scrambled.
Welcome to my nightmare. Ham radio operators have been dealing with the wall wart and other devices EMI/RFI for many years. It only gets worse with new and more insidious sources of electrical noise arriving every day. For example, I recently found a garden path full of these LED lights. Each one has a built in switcher with little filtering and no shielding. Ferrite beads around the leads were a big help.
"A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing" I do some computah work for the author. I recently unloaded about 50 lbs of linear wall warts on his doorstep. Over the years, he has systematically replaced as many switchers with linear power supplies as possible. The few switchers that can't be replaced, have large common mode toroids on both input and output leads. Something like these:
See list of his other publications for other articles: such as: "Power Line Filters"
If you're going to be chasing down sources of EMI and RFI, the best technique is to kill the power to sections of the house at the breaker box. This doesn't do anything for battery backed up devices, such as digital clocks, or deal with neighborhood sources, but otherwise works well. For fine tuning, I use an AM portable receiver tuned to empty HF frequencies. I use an Alinco DJ-X2 but any portable AM/FM/SW/AIR receiver will work. When I'm dealing with more exotic noise sources, I use a spectrum analyzers.
I haven't done any bench tests with an LISN (line impedance stabilization network) comparing various switchers. Powerstream does not actually manufacture the products they sell but buys them from various vendors: My guess(tm) is that I would expect wide variations in EMI radiation characteristics. The various genuine Apple power supplies that I own seem fairly quiet for both conducted and radiated noise, but not totally quiet. An external filter would still be useful. I don't know how they compare with counterfeit and cloned Apple power supplies or similar switchers.
Jeff Liebermann firstname.lastname@example.org
150 Felker St #D http://www.LearnByDestroying.com