Can Switching Power Supplies Be Quiet?

Over the years, there has been considerable discussion among DX-ers surrounding switching power supplies, particularly due to their tendency to generate radio frequency interference (RFI) affecting radio reception. German DX-er Werner Karn prompted me to revisit a manufacturer I had previously tested, after sharing on the Perseus reflector that his Perseus22 was being powered noise-free by a medical-grade 9V supply from Mean Well.

I had, in fact, evaluated Mean Well supplies many years ago during my quest for a suitable solution for my KiwiSDRs. While they performed reasonably well, they weren’t entirely noise-free, which led me to the tongue-in-cheek conclusion that “they meant well” but hadn’t quite hit the mark. It turns out, however, that Mean Well offers supplies in varying grades of quality. The one I had tried was an “industrial grade” GST-type unit, whereas Werner had opted for a “medical grade” GSM-type 9V model.

This piqued my interest, so I ordered a selection of 5V, 12V, and 19V models—the latter intended to replace a rather noisy PSU for a Dell micro desktop PC, affecting the lower shortwave bands. I’ve now tested all of them, and there's no sign of RFI whatsoever.

From what I can observe—literally, judging by pre- and post-test waterfall displays—none of the units produces any detectable noise across the frequencies we care about, i.e. 0–30 MHz, and especially MW.

They all look alike, so I had to add a bit of extra voltage info...

It’s my view that manufacturers of DC-powered devices tend to favour low-cost power supplies to keep expenses down, especially since end-users rarely pay attention to such details. Even reputable makers of commercial-grade routers like Teltonika adopt this approach. Yet quality supplies needn't cost the earth. A 4A, 9VDC medical-grade PSU suitable for the Perseus22 sells for around €20 each, roughly 1% of the radio’s retail price, and significantly less when purchased in bulk.

I’m not suggesting Mean Well is the sole producer of low-noise switching power supplies. I simply lack the time or resources to comprehensively survey that market. Still, the medical-grade GSM-type units I’ve acquired are as quiet as a traditional linear power supply.

Just a heads-up if you’re planning to order one (or several): the default DC connector is a 2.1 mm barrel plug (2.1×5.5 mm). They also offer adaptors for various other connectors at very fair prices—usually under €0.50. Also note that you’ll need a separate mains cable with a C7 connector—commonly known as a “figure 8” or “shotgun” plug. The plug converter guide looks like the image below.

See link above for better resolution

Mean Well is a Taiwanese firm. That may be of interest if you take geopolitical factors into account when making purchase decisions—I know I do. Yet, the actual product is made in China. So, there you go.