Power Supply Considerations

I have put about 10 KiwiSDR into service over the years and here's a few thoughts on PSU

  • "wall warts" are varied, as there as older linear ones, simple chargers, switchers with actual filtering for RFI/EMI
  • assume warts to be suspect and test them thoroughly for both radiated and conducted noise
  • Linear PSU are almost always a safe choice but are inefficient and their power consumption impacts your electric bill and any UPS run-time
  • Industrial Switcher Units are usually quiet and usable
  • I am using Meanwell DIN Rail mounted PSU in a few installations and they are available on Amazon, reasonably priced, and appear to be quiet.


  • I used switched mode supplies nearly all the time these days.

    The only problem I occasionally find is that despite lots of filtering it is very difficult to entirely remove the switching noise on the VLF bands, typically <100 kHz that is produced by older designs.

    More mosern deigns with switching frequencies in the region of 1 to 2 MHz are a lot easier to filter and are also generally more efficient.



  • After starting a new receiver on short waves, I received interference from a switching power supply. Partially they were reduced by a power filter in front of the 220 volt outlet. I'm thinking of using a 12 volt transformer power supply and a 5 volt switching converter with a high frequency of 1.5 MHz. I remember someone already sharing this idea here on the forum. But I can't find this thread. Can someone remember? Thank you!

  • Search the forum for MP1584



  • edited March 10

    Martin, this is exactly what I was looking for. Thank you for experimenting with the power supply!

    In most of the ready-made modules, a 100kOhm resistor is installed on the MP1584, which sets the frequency of PWM operation. You can reduce its resistance and raise the frequency from 1 MHz to 1.5 MHz. Perhaps this will further reduce interference.

  • Regarding discussion on whether the switched power supply is noisier than a good old transformer. A softrock style receiver was noisier on a transformer DC power supply than on an old DANCALL switched power supply made for NMT phones. The explanation is simple: The mains is noisy from all the switched power supplies around the house. There is a filter at the mains side of the DANCALL switched supply that stops the noise coming through to the DC side. Thus a mains filter is likely a good idea even with a transformer type non-switched wall wart.

    73, Vojtech OK1IAK

  • Back when I purchased my Kiwi, I decided I wanted the quietest power supply possible... so I built my own! :) It's 100% linear/analog, dual regulated. It has an AC input filter. The 16V from the transformer is regulated down to 12, which is further regulated down to 5. Unfortunately, my neighborhood has a LOT of RF noise... even on a battery-powered portable radio, I hear a significant amount of static on a large swath of frequencies from 200KHz well into the upper SW bands. On my Kiwi, it shows WIDE swaths of S7+ noise levels.

    As for setting a new supply to run at 1.5MHz... that would block out a semi-local AM station I listen to now and then. :(

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