Switch Mode Power Supply Noise

I am the owner of quite a few 12VDC power supplies. All of them are switch mode type. Among the many I own is an Alinco 40A supply that was built with Amateur Radio HF operating in mind. As such it produces very electrical little noise that can be detected by my various ham radio receivers. That cannot be said for the other supplies. Most of which look like the one below.

I recently moved much of my radio shack onto the wall in the garage and that required me to also mount the power supply on the wall. The supply would drive not only a handful of radio's but also an ever growing farm of Raspberry Pi computers as seen in the image below.

In this picture we can see the Raspberry Pi farm as well as a few radio's. What you cannot see is my Afedrfi SDR-Net network attached SDR HF receiver and the AllStarLink system I host for the Marple-Newtown Amateur Radio Club. All of these systems and receivers are powered by a no-name Chinese 30Amp switch mode power supply like the one pictured above.

HF operations in the house have recently been plagues by a large amount of electrical noise. I had my suspicions as to where it was coming from and so started an investigation to prove my theory. My first test was to document the noise level under "normal" conditions. This would be where all the radio's and Raspberry Pi's are powered by the 30A supply. Using my SDR receiver connected to my copy of the GQRX Software Defined Radio tools I was able to take a screen shot of the entire 40 meter amateur band and also quite a bit of the 41 meter broadcast band too.

In the above picture we can see a uniform interference pattern every roughly every 50KHz or so. This interference is found all the way up the spectrum from below the AM broadcast band to well after my receiver caps out at 45MHz. It it strongest at the low end of the bands and diminishes (but does not disappear) at the top. Below is my a capture of my local AM radio spectrum.

So now that I have a baseline I elected to turn off the supply and replace it with one of my camping batteries. I expected a very quiet spectrum response. I was not disappointed. As you can see, a significant drop in the noise levels. Look carefully and you can make out not only proper AM carriers but also IBOC carriers too.

Further up the bad there is almost no electrical noise at all.

Changing to a different no-name brand of supply we get this.

Not as bad as the first supply but not great either. But it diminishes quickly as the frequency gets higher.

I am led to believe that the Meanwell brand of switch mode PSU's upon which most of the ones I have are clones behave much better. I have yet to experience this as I do not own one. However, they are currently (pre-Trump trade war Tariffs) only around $40 so I am trying to obtain one.