Interference question

[radio nut]

Thank you, I will check. I haven't had a tube radio in my house for years because of this issue.

[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..

[Electronic M]

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.

[mr_rye89]

For a while there I had some noise that was pegging the S meter on my Icom transceiver anytime I wanted to talk on 40/80M (7 mhz and 3.8mhz). Turned out to be the 12 volt switcher that fed my sat receiver. Swapped it out for another, problem solved! Somehow my solar setup isn't too noisy, which is surprising as I have one of those cheapo high frequency "pure sine" inverters. It's not grid tied if that makes a difference.

Yeah walk around the house and hunt for the noise and/or start flipping breakers.

[vortalexfan]

Originally Posted by Electronic M

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.

I wasn't talking about a wall wart style charger, I was talking about the type that you can charge up and take with you to charge a phone or wireless earbuds when you don't have an AC wall wart to use, like the one pictured below.

[mr_rye89]

Originally Posted by vortalexfan

I wasn't talking about a wall wart style charger, I was talking about the type that you can charge up and take with you to charge a phone or wireless earbuds when you don't have an AC wall wart to use, like the one pictured below.

I didn't even think about those being a source of noise. I had my (tr)usdx HF radio plugged into one yesterday (for lower power output while I was tuning the reference frequency). Luckily my power bank isn't noisy.