Every HF station needs a steady source of 12 to 14 volts DC, and the box that provides it gets less attention than the radio or antenna sitting next to it. That's a shame, because the power supply can quietly make or break your receive audio. Understanding the real differences between linear and switching designs helps you pick the right one, and know what to do if the one you already own is hissing into your headphones.
Two Very Different Ways to Make DC
A linear supply takes AC from the wall, steps it down with a transformer, then smooths and regulates it with a bank of capacitors and pass transistors. It's an old, simple, well-understood design. A switching supply instead rectifies the incoming AC, then chops it at a high frequency, often tens or hundreds of kilohertz, through a small transformer before smoothing it back into clean DC. That switching action is what makes the supply light and efficient, and it's also the reason switchers have a reputation for causing radio frequency interference (RFI).
Linear Supplies: The Quiet Heavyweight
Linear supplies are prized in ham shacks for one big reason: they are electrically very quiet. Because there's no high-frequency switching happening inside, a well-built linear supply adds essentially no noise to your receiver. The trade-off is size and weight. The transformer needed to handle real current at 60 Hz (or 50 Hz outside North America) is large and heavy, so a linear supply capable of running a 100-watt HF rig can weigh 20 pounds or more. They also run warmer, since linear regulation wastes the difference between input and output voltage as heat, and they generally cost more per amp of capacity than an equivalent switcher.
Switching Supplies: Light, Efficient and Popular
Switching supplies have taken over most of the market for good reasons. They're compact enough to tuck into a go-bag, run cooler because they waste less energy as heat, and typically cost less for the same current rating. For portable operating, Field Day, or a shack where desk space is tight, a switcher is often the practical choice. The catch is that the switching frequency and its harmonics can radiate or conduct into your receive path, showing up as a buzz, whine, or picket-fence noise that rides right across the HF bands, especially on the lower bands where atmospheric noise would normally be low.
Where the Noise Actually Comes From
Switching noise reaches your receiver two ways: conducted, traveling along the DC power leads and even back through the AC mains, and radiated, coming straight off the supply's case, transformer, and PCB traces. A supply with poor internal filtering, a thin or missing metal enclosure, or long unshielded DC leads will radiate more. The problem is usually worse on lower bands and weaker on VHF/UHF, and it tends to change pitch or intensity with the load the radio is drawing, which is a useful clue when you're trying to identify the source.
Not All Switchers Are Equal
It's worth separating "switching supply" from "noisy supply." Many modern switching supplies, including several designed specifically for amateur radio, use good input and output filtering, shielded enclosures, and careful layout to keep noise well below what a receiver will notice. Cheap generic supplies built for other purposes, like ones intended for LED lighting or general electronics, often skip that filtering entirely because it isn't needed for their original application. If you're shopping, a supply explicitly marketed for ham radio or amateur transceiver use has usually been vetted for RF cleanliness, though that's a general trend rather than a guarantee.
Taming Switching-Supply RFI
If you already own a switcher and it's noisy, don't assume you need to replace it. Work through the troubleshooting order above. Start by confirming the supply really is the source: switch it off, run the radio on a battery for a minute, and listen. If the noise disappears, you've confirmed the culprit and can move on to fixes rather than chasing something else in the shack.
Grounding, Bonding and Cable Dressing
Physical layout solves a surprising amount of switcher noise. Keep DC power leads as short as practical, and where they must run near coax or antenna feedlines, cross them at a right angle rather than running them in parallel for any distance. Bond the supply's chassis to your station ground with a short, wide strap rather than a thin wire, since a longer ground path behaves more like an antenna at RF. Clip-on ferrite chokes on the DC leads close to the supply's output are inexpensive and often knock down conducted noise noticeably; a few turns through the ferrite usually work better than a single pass. A dedicated DC line filter between the supply and the radio can help further if ferrites alone aren't enough.
Sizing the Supply So It Isn't Straining
An undersized supply running near its maximum rating tends to run hotter and can be noisier, since the switching regulator works harder to hold voltage steady under load. Choose a supply rated comfortably above your radio's peak transmit current, not just its average draw, so it operates well within its comfort zone. If you want the details on matching a supply to your specific radio, see our guide to sizing a 13.8V supply, and if you're building out backup power as well, our emergency power plan covers batteries alongside your main supply.
Common Mistakes
- Blaming the antenna or band conditions before ruling out the supply with a simple power-off test
- Running DC leads bundled tightly alongside coax for several feet
- Using a generic, unshielded switcher meant for a completely different application
- Grounding the supply with a long, thin wire instead of a short strap
- Ignoring a supply that's running near its maximum rated current continuously
Which One Should You Choose?
For a fixed base station where weight and portability don't matter, a good linear supply remains a safe, quiet choice, particularly for weak-signal or DX work where every bit of noise floor matters. For portable, field, or space-constrained setups, a well-reviewed switching supply designed for amateur use gives you nearly the same performance in a fraction of the weight, provided you take the filtering steps above seriously. Many operators end up with one of each: a linear supply on the main desk and a compact switcher for the go-bag.
A Quick Pre-Purchase and Troubleshooting Checklist
- Check the rated continuous current against your radio's actual peak draw, not just its average
- Favor supplies marketed for amateur radio use or with a track record among other hams
- Test for noise with the radio on receive before you commit to a permanent installation
- Keep DC leads short and separated from antenna feedlines
- Bond the chassis with a short, heavy ground strap
- Have a few clip-on ferrite chokes on hand for DC leads
- Know your return policy in case a specific unit turns out to be noisy
Wrap-Up
Linear and switching supplies both have a legitimate place in a ham shack, and the choice really comes down to what you're optimizing for: silence and simplicity, or weight and efficiency. If you go the switching route, treat filtering, grounding and cable dressing as part of the installation, not an afterthought, and you can usually get receive performance close to what a linear supply offers. Before you chase noise as an antenna or propagation problem, it's always worth a quick check of the live HF propagation page to rule out conditions, and a fast power-off test to see whether your supply is the real source. Once your noise floor is under control, the ham radio FAQ and quick reference page are handy for the next question that comes up in the shack.
How HamRadioList can help
Once your shack is quiet, check the {{svc:propagation|live HF propagation page}} to know whether a weak band is really dead or just drowned by noise, and log the contacts you make once the noise is gone in the free {{svc:logbook|online logbook}}. If your supply lives at a remote site, {{svc:remote_rig|Remote Rig}} and {{svc:station_bridge|Station Bridge}} are worth a look too.
- Live HF propagation - see current band conditions before you call CQ.
- Remote Rig - operate your own radio from anywhere on Android, iPhone, Windows or Linux, with live push-to-talk audio and CAT control.
- Station Bridge - the software that connects your radio, audio interface and computer to Remote Rig.
- Free online ham radio logbook - log every contact, import and export ADIF, sync with QRZ.com and keep your awards organised.
- Ham radio FAQ - plain answers to the questions new operators ask most.
New here, or getting back on the air? Create your free HamRadioList account to log contacts, check band conditions and practise for your exam, or browse more guides from the blog. HamRadioList is built by amateur radio operators in Nova Scotia for operators everywhere.