A rigorous, myth-free comparison of the two dominant power-supply architectures — what they are, how they differ, and how to make an informed choice for your station.
Amateur radio transceivers place demanding requirements on their DC power sources. A modern 100-watt transceiver commonly draws a little over 20 amperes during transmit — a load that the power supply must sustain reliably, with minimal noise contribution to the receive and transmit signal chain.[1][2]
Two fundamentally different supply architectures are available to the amateur operator: the linear regulated supply and the switch-mode power supply (SMPS). Each carries a distinct set of engineering trade-offs, and neither deserves blanket praise or condemnation without context.
A linear supply begins with a large laminated-iron transformer, which steps the mains AC voltage down to a level near the desired output. That lower-voltage AC is then rectified to pulsating DC, filtered with bulk capacitance to reduce ripple, and passed through a series-pass regulator operating in its linear region to produce a stable regulated output.[3]
The operative word here is linear: the regulator dissipates the difference between input and output as heat. This is inherently less efficient than a switch-mode approach, but it can produce very clean DC. In the Astron RM-60M, for example, the listed ripple is less than 5 mV peak-to-peak at full load and low line.[4] The penalty is size and mass. That large 50/60 Hz transformer is heavy, and there is no practical way around that low-frequency magnetics requirement.
An SMPS takes a fundamentally different approach. The incoming mains AC is first rectified and filtered directly to high-voltage DC — about 160 VDC from nominal 120 VAC mains, or about 310 VDC from nominal 230 VAC mains. That DC is then switched at high frequency through a much smaller ferrite-core transformer or inductor structure.[5]
The key principle is straightforward: increasing switching frequency allows the magnetic components to become much smaller for a given power level. In practical equipment, this is why an SMPS can be dramatically smaller and lighter than a comparable 50/60 Hz linear supply.[6]
| Specification | Astron RM-60M (Linear) | TekPower TP50SW (SMPS) |
|---|---|---|
| Output current | 50 A continuous / 55 A ICS | 50 A maximum |
| Listed dimensions | 7 × 19 × 12.5 inches | 7.7 × 3.4 × 11 inches |
| Listed weight | 55 lb shipping weight | 6 lb |
| Representative current retail price | $759.95 | $179.00 |
| Listed ripple / noise | < 5 mV peak-to-peak | < 100 mV peak-to-peak |
Using these representative current listings, the SMPS is roughly 80% smaller by enclosure volume and nearly 90% lighter by listed weight, while also selling for far less. For portable operation, expeditions, or any installation where rack space, transport, or shelf loading matters, that is a substantial practical advantage.[4][7][8][9]
The Astron RM-60M lists less than 5 mV peak-to-peak ripple, while the TekPower TP50SW is listed at less than 100 mV peak-to-peak.[4][7] Modern amateur transceivers do include internal regulation and decoupling, but it is still prudent to avoid assuming that supply-borne noise is irrelevant. Lower conducted noise at the source is always preferable.
The more significant concern with SMPS designs is not merely output ripple, but the generation of high-frequency switching noise. The switching devices handle fast voltage and current transitions, producing harmonic energy that can appear as conducted noise on the DC output and AC mains, and as radiated interference from internal loops, wiring, and magnetic components.[10]
In the United States, equipment of this type is commonly evaluated under FCC Part 15 conducted-emissions limits from 150 kHz to 30 MHz.[11] For radiated emissions under Part 15 Subpart B, the general limits for unintentional radiators begin above 30 MHz.[12] In international EMC practice, the legacy CISPR 22 / EN 55022 framework has been superseded by CISPR 32 / EN 55032, but the same basic point remains: below 30 MHz, mains-port conducted emissions are a central part of compliance testing.[13][14]
A Class B conducted limit of 316 µV across 50 ohms corresponds to about −57 dBm. A product can meet the conducted-emissions limit at the mains port and still create a very noticeable HF noise problem in a real station, depending on installation and coupling paths.[15][16]
| Standard | Class A limit | Class B limit |
|---|---|---|
| FCC Part 15.107 (1.705–30 MHz) | 3,000 µV | 250 µV |
| CISPR 22 / EN 55022 legacy limit (0.5–5 MHz) | 1,000 µV | 316 µV (average) |
The noise performance of any given SMPS depends heavily on design quality: input filtering, snubbers or clamps around switching devices, output filtering, loop-area control, PCB layout, shielding, and grounding all matter.[10]
It is also worth noting that linear supplies are not automatically immune to a noisy AC environment. In a practical station, conducted mains noise from other devices can still enter the shack power system. A well-filtered SMPS may reject some of that noise better than a minimally filtered linear supply. Whether that happens in a given installation is design-dependent, not architecture-dependent.
The binary framing of “linear supplies are quiet; switch-mode supplies are noisy” is technically imprecise and operationally unhelpful. Both architectures can produce excellent results; both can produce poor results. The determining factors are design quality, manufacturing standards, compliance discipline, and the specific application.