Power Supplies and Batteries for Ham Radio

Amateur transceivers run on a nominal 13.8 volts DC, which is the voltage of a charged twelve-volt lead-acid battery. Everything in the station ultimately depends on that supply being stable, quiet and able to deliver the current the radio draws on transmit.

The failure mode is quiet and gradual. A supply that cannot hold voltage under load causes reduced transmit power and distorted audio. A supply with excessive ripple puts hum and hash on the signal that no amount of digital processing will remove.

Sizing the supply

The number that matters is the continuous current at full transmit power, not the average current, and not the figure printed on the box. A 100 W HF transceiver typically draws 20 to 22 amps on SSB peaks and slightly more on continuous carriers like FM or digital modes.

Add headroom. A supply rated at exactly the radio current will be running at its limit and will sag. A 30 amp supply for a 20 amp radio runs cooler, lasts longer and holds voltage better.

Ripple and noise

Ripple is the residual AC on the DC output. A linear supply with a large reservoir capacitor and a good regulator can hold ripple below a few millivolts, which is inaudible. A poorly designed switching supply can put switching hash across the HF spectrum, where it appears as a raised noise floor or a series of birdies.

This is not an argument against switching supplies — a good one is efficient, light and quiet. It is an argument for checking. Listen on a quiet frequency with the supply connected and disconnected; if the noise floor changes, the supply is the problem.

Batteries

For portable work and for mains failure, a battery bank is essential. Lead-acid is cheap and heavy and should not be discharged below half its rated capacity. Lithium iron phosphate costs more and weighs far less, tolerates deeper discharge, and holds voltage better under load.