Quote:
Originally Posted by vortalexfan
I was having the same issue with a couple of my battery operated radios and it turned out that those portable charging bricks that you can use to quickly recharge a cell phone or MP3 player (such as an iPod or even wireless earbuds or headphones) was putting out some interference which is interesting because they are strictly battery powered and shouldn't have to rely on a SMPS, but apparently they do (or at least something similar) so then I just try and keep those away from my radios.
Another weird thing about those portable charging bricks is that they seem to put out interference regardless of whether they are plugged in and charging and or charging something or not..   |
Modern wall warts and 120V to USB chargers use switch mode power supplies and regulators instead of the 60Hz transformers and linear regulators they used 20 years ago.
Switch mode supplies typically use 17KHz square waves. As Fourrier proved mathematically a square wave is made up of sine waves... Specifically one at the fundamental and an infinite series of multiples of the fundamental each a higher frequency than the last. As frequency increases amplitude decreases, but radios are sensitive to very low amplitude.
The makers of these devices could keep the square waves from interfering by filtering and or shielding the supply to keep these signals from conducting down cables and or radiating, but many makers, especially China, simply don't care enough to do it.