Choosing a Power Supply for Ham Radio: Switching, Linear, or Battery
Why radios do not run on mains
Almost every amateur transceiver works from 13.8 volts DC. The number is not arbitrary: it is the typical voltage of a vehicle electrical system with the engine running, so the same radio can live on a bench supply at home and a car battery on the road. Apart from a few base stations and amplifiers with built-in mains supplies, you will need a 13.8 V DC source of some kind — a power supply or a battery.
Size the current first
The first specification to check is output current. The method is simple: find the radio’s maximum transmit current in the manual, then choose a supply comfortably above it.
Practical figures look like this:
- 5 W handheld: about 1.5 A — a battery covers it
- 50 W mobile: about 10–12 A — pair it with a 15 A supply
- 100 W HF transceiver: about 20–25 A at full power — use a 30 A-class supply
- High-power amplifier: 80 A or more
“Bigger is safer” is close to a law here. A radio draws only the current it needs and will not be damaged by an oversized supply; an undersized one sags the moment you key up, which shows up as reduced power, overheating, or the radio restarting mid-transmission. Manufacturer data makes the point concrete: the Icom IC-7300 draws about 21 A at 100 W output, and the Yaesu FT-891 about 23 A — both want a 30 A-class continuous rating, not an intermittent peak figure.
Beyond current, two more specs deserve attention. Ripple should be as low as possible; excessive ripple turns into audible hum. Protection matters just as much — reverse-polarity, short-circuit, over-voltage, and over-current protection. An unprotected supply can take your final transistors with it the first time a lead is connected backwards.
Switching or linear
This is the most debated choice in station power.
Switching supplies rectify the mains to high-voltage DC and then chop it through a high-frequency transformer, typically switching somewhere between 20 and 500 kHz. The results: efficiency usually above 80 percent, small size, roughly a third to a half of the weight of a linear unit, low cost, and easy scaling to high current. For most shacks, a switching supply is the right default.
Its weakness is inherent to the switching itself: those fast transitions generate electromagnetic interference. Quality units suppress it well; cheap ones spray hash across the spectrum, and you hear it as a background hiss or hum that buries weak signals — especially painful on CW and FT8.
Linear supplies use a bulky mains-frequency transformer, then rectify, filter, and regulate the old-fashioned way. The output is extremely clean, with ripple in the millivolt range and essentially no switching noise; the circuits are simple and famously long-lived. The bill comes due elsewhere: efficiency is typically only in the 50–60 percent range, heat output is substantial, a 10 A linear unit can weigh 5 to 10 kg, and the price is two to three times a switcher of the same rating. Portability is out of the question.
The honest conclusion: switching is the general-purpose answer; linear is for people who chase the last fraction of a dB of receive noise floor and accept the weight and cost. For VHF/UHF work, mobile use, or casual HF, a good switcher is enough. For weak-signal HF work where every dB counts, a linear supply’s silence is genuinely addictive.
On a budget with low noise as the goal, there is a third path: a switcher explicitly marketed as low-RFI — several include a small control that shifts the switching frequency to move any residual noise off your operating frequency — combined with the noise-reduction habits below. That is usually the best value.
Batteries: the right answer for the field
For portable activations, emergency backup, and anything away from the mains, a battery beats any supply.
- LiFePO4 (lithium iron phosphate): nominally 12.8 V, light, safe chemistry, thousands of cycles (2000+). Common sizes run 12 V at 10–20 Ah. The default choice for portable operating. A 6 Ah pack runs a QRP station all day, or a 100 W radio for a couple of hours of casual use.
- Lead-acid: cheap and capable of high discharge current, but heavy. One caution that is often skipped: lead-acid batteries vent hydrogen while charging and discharging, so they need ventilation — a sealed room is not an acceptable location.
- LiPo: light with high discharge capability, but demanding about charge management and genuinely unsafe when mistreated. Not a beginner’s battery.
Whatever the chemistry, do not ask a small battery to feed a high-power radio. Heavy current draw overheats the pack and collapses its voltage; both end the fun early.
Wiring rules that are not optional
- Gauge the wire properly. For 20 A runs, use at least 2.5 mm² copper, and heavier for long runs; in vehicle installations, conductor cross-section above 4 mm² is the safer habit.
- Fuse the positive lead. At roughly 1.2 to 1.5 times the maximum operating current, installed close to the source terminal.
- Choose the right connector. Anderson Powerpole is the amateur standard for high-current connections — reliable, genderless, and hot-pluggable.
- Ground the chassis. A metal-cased supply should be solidly grounded.
- Keep DC leads away from feed lines. Route them separately; do not bundle them together.
If your switching supply is noisy
Do not order a linear supply yet. Try three things first:
- Add filtering. Filters at the input and output, or a few turns of the DC cable through a ferrite core (a common-mode choke) to keep RF from escaping down the lead.
- Increase distance. Move the supply away from the radio and antenna, shorten the DC run, and use shielded cable if needed.
- Fix grounding. Bonding the supply chassis and the radio into one grounded system often does more than any ferrite.
DIY supplies: the safety triangle
If you build your own, three rules are non-negotiable: a three-wire mains cord, a metal enclosure, and the enclosure reliably bonded to the mains earth. Twelve volts sounds harmless, but the instantaneous currents involved in high-power service can throw an arc capable of starting a fire. “It’s only low voltage” is not a safety plan.
References
- Radio Society of Great Britain (RSGB) — “Other equipment you may need”, rsgb.org (accessed 2026)
- National Amateur Radio Alliance — “Power, supplies and batteries”, wiki.usnara.org (accessed 2026)
- DXRadar — “Best Power Supply for Ham Radio: 13.8V Sizing Done Right” (2026)
- CommsGearReport — “Understanding Amateur Radio Power Supplies: Your Station’s Foundation” (2026)
- Icom Europe — IC-7300 specifications (power consumption, 21 A at 100 W) (accessed 2026)
- Yaesu — FT-891 specifications (current consumption, 23 A transmit) (accessed 2026)