Power supply sizing guide

How to size a power supply

A power supply must provide enough current for your transceiver at full transmit power plus all accessories running simultaneously. Undersized power supplies cause voltage sag on transmit, which reduces power output and can damage the power supply.

The rule of thumb

A 100W HF transceiver draws approximately 20-22A on SSB transmit peaks. Add 2-5A for accessories (antenna tuner, computer, monitor, etc.). A 30A power supply provides adequate margin for a 100W station. A 50W VHF/UHF mobile draws approximately 10-12A on transmit.

Linear vs switching

Linear (Astron RS-series): Heavy, clean DC, low RF noise. The traditional choice. 20+ year lifespan. Produces clean DC with minimal ripple and no switching noise. Preferred by operators concerned about receiver noise floor.

Switching (Powerwerx, Samlex, MFJ): Light, compact, affordable. Modern switching supplies have good RF noise performance but some operators report elevated noise floors on sensitive receivers. Fan noise under load. 10-15 year typical lifespan.

Sizing table