Does this PSU seem adequate for two KiwiSDR's?

While testing a new KiwiSDR + BBG, I've been powering it with this PSU:

The output amperage is stated differently in several places, but it appears to be 3.5A.

I'm planning to add a second KiwiSDR. Does the above PSU seem as though it would be adequate for two? I see it stated here that the receivers peak at about 1.5A each.


  • While that might work for two Kiwis, especially if they start at different times, some of us have turned to an inexpensive alternative. While these run from DC rather than mains AC and one has to provide that separately, and while they are SMPS so do have fast edges capable of QRMing a Kiwi, they run at ~ 1MHz and in practice can work very well.

    You might want to consider trying these, one per Kiwi, from whatever inexpensive ~12V DC supply you might have battery or otherwise before going the route you ask about. SUch a solution could be more flexible and cheaper.

  • Thanks, I've seen those mentioned, and they're certainly inexpensive to try.

    Are certain bands known to be affected more by noise from the buck converters?

  • PS noise is generally due to conducted, common mode noise current. The Kiwi is pretty impervious to differential noise so more C's or series L's don't usually help.

    These small, cheap supplies have a high switching frequency and because they are small and by design most circulating currents are contained within them rather than injected on the input and output lines.

    It's not uncommon to not be able to even find the ~960 kHz fundamental or its harmonics anywhere in an operating Kiwi. I use them on receivers that reach or exceed the ITU propagated noise floor.

    I suggest identifying the frequency of the line and verifying that it is not an impairment to Kiwi operation at first but other than setting the V to 5.25VDC or so ahead of time and perhaps shrink tube wrapping the whole thing (takes a larger diameter shrink to fit but they are pretty small so should be available) it's not necessary to do much.

  • edited April 2022

    On the original PSU question, I have a similar (internal transformer) linear and it would run two standard Kiwi's without issue but as n6gn highlights, the issues are most problematic at boot so if you have a momentary power failure there is a small chance that one or more would not boot due to the strict power control on the BeagleBone.

    The UK listed version calls it a 25W PSU but says don't add anything else after 3.5A,5.1V (17.85W) which is more realistic (and fine for two BBG Kiwi's).

    I think I also went down the small DC-DC (MP1584 based) after seeing it mentioned on here and they are remarkable considering the cost and size. I fed them from "AnyOld" 12V linear supply or 12V lead acid from solar, knowing the supply to them can be up to 28V (I think) gives a nice level of protection.

    Don't be tempted to "Upgrade" to the larger DC-DC (LM2596) with multiturn pots and up to 35V input, 3.5A out as they are much noisier in my experience.

  • Thanks, I'll try using the 5V 3.5A PSU with the two KiwiSDR's for now, then work with the buck converters. It would be nice to consolidate all 12vdc and 5vdc devices to use a single power source.

  • Hi All,

    A bit of an old thread, but I've just go around to putting my home KiWi inside a screened metal box in order to try and cut down on the overall amount of RF noise in the workshop.

    As part of this I thought I would try one of the MP1584 DC-DC convertor boards previously mentioned. I had already used some similar board for other projects, but I wasn't quite prepared for just how small these ones are.

    After some load tests on the bench, just to make sure they worked as advertised, I decided to connect one with my KiWi. The plan was that if this worked, I could get rid of the separate 5v power supply and just run it from my big 12v power supply that already feeds everything else.

    I mounted the board inside a small screened metal box I'd made by solding together sections of brass sheet.

    Some quick tests revealed that it was producing quite a bit of broadband noise on frequencies up to about 1MHz, with a strong carrier at just below 1MHz, which was very noticeable.

    Adding some 10uF 25v ceramic SMD capacitors directly across the input and output -ve and +ve terminals reduced the level of this carrier by about 25dB, and it also dropped the level of the broadband noise by a significant amount too.

    Adding some 22uH (low resistance moulded chokes I found in my junk pile) series connected input and output inductors on the +ve supply rails, and another pair of capacitors to ground on the input and output side of the inductors, was used to form a Pi section low pass filter. I then used some thin coax to take the DC in and the DC out to the existing KiWi input DC voltage connector. However I took the -ve screen of the coax directly to the KiWi 0v rail, as everything else was directly grounded, and I didn't want to place a short across one section of the balanced input choke, as this would affect the choking action.

    Doing all of this has brought the level of emissions down still further, and I'm now able to place the DC-DC convertor board, directly inside the screened box that the KiWi resides in.

    With a 50 ohm load on the KiWi input, I now cannot detect the approx 1MHz switching carrier, and the broadband noise is almost completely gone. There are a couple of low level warbling carriers at around 2MHz, which I've not so far been able to trace the source of, but apart from that it's all pretty good. Once an antenna is connected, all of these interally generated signals just get lost among all the other directly received interference, so it's not really a problem.

    The current draw at 12v is surprisingly small (in comparision to the current draw at 5v) at around 300mA, so overall I'm pretty pleased with the end result.

    One key takeaway from all of this is that if your KiWi is still in its original plastic enclosure, spend a bit of time finding a metal screened case for it. It's made a huge difference to the overall noise floor in the workshop, and is much less likely to be contributing to the general level of received interference I hear on my KiWi in its urban setting.

    My thanks to folks for recommending these DC-DC convertor boards, which I'm sure I will use elsewhere, with a bit of care and some additional filtering :-)



  • Hi Martin,

    My apologies for not having seen your post until now.

    Your comments certainly inspire me to improve the shielding of my KiwiSDR. Do you have any photos of your screened metal box? That might give me some ideas.

    Also, you mentioned using inductors and capacitors to form a Pi section low pass filter. I'm not clear on the filter's purpose. There's a noise source above the frequency range your Kiwi covers?

    Thanks much,


  • edited September 26

    Hi Frank,

    Here's a quick snapshot.

    I moved the position of the DC-DC convertor box around until I got the least spurs and interference when the RF input was terminated with a 50 ohm load. It ended up being soldered to the lids of the lids of the GPS and RF stage. I also had to add some short wire links between the coax sockets on the box and board, as there was too much of a current / voltage differential between them when just the pre-made short coax cables were being used alone.

    The DC filter is a 10uF SMD cap to ground, a series 22uH choke and another 10uF SMD cap to ground. This was to filter off any remaining 1MHz switching frequency and noise / harmonics that may have been carried by the DC in and out cables. I also used screened cable for the DC connections in order to minimise any other cross coupling between the cables.

    I hope this provides you with some further ideas.



  • Thanks! It does indeed.

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