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Removing Switched Mode Power Supplies from Shack

removing switched mode power supplies

Removing switched mode power supplies, and their attendant RFI, can be quite simple. Let’s take a look at my cheep and cheerful approach.

Pretty much all of your radio room accessories came with a switched mode power supply (wall-wart) that creates at least some RFI. Over time, as you add accessories you buy power bars for these supplies. Most of these power bars claim EMI filtering but that’s a joke for RFI.

Recently, while I was sniffing for RFI in my connection cables using a battery-powered spectrum analyzer, I was amazed at how much RFI was leaking into my supposedly shielded cables. As I unplugged these accessory SMPS, I was further amazed at how much the broad spectrum of interference went down, and down, and down.

So, I did an inventory and found six SMPS that would be easy to replace. All provided nominal 12 VDC at currents ranging from 150 mA to 1 amp. All but one used the ubiquitous 2.1 by 5.5 mm coaxial power connector with positive tip. I could easily replace all of these with a single linear power supply, so I did.

Old fashioned linear power supplies create no RFI because they use magnetic transformers and rectifiers. No free running oscillators, no chopping and switching, no radio frequency interference. Plain and simple.

Removing switched mode power supplies just requires some new wiring harnesses and a distribution system of some sort. Some folks use Anderson Power Poles, but I decided to create my own standard solution.

Removing Switched Mode Power Supplies Yourself

First, get a 12 VDC linear power supply. You can buy these new for $50 and up, at flea markets for $20. If you are a ham of a certain age, you probably already have a few lying around. Typically, these provide 3-5 amps continuous.

Second, get yourself some coax power connector adaptors online. These are used mainly for CCTV interconnection, have the 2.1 mm inner diameter standard, and are available as both plugs or jacks. You can get a bunch for a few dollars. Since they come with screw terminals you can avoid soldering onto tiny connectors. Some of you older devices may use 2.5 mm ID, so you will perhaps need to solder some of these.

Finally, some 20 or 22 AWG stranded two conductor wire, even speaker wire, and spade terminals, preferably soldered but crimp can work. Just make sure your wire is heavy enough for maximum current draw.

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