Products & Product Reviews

Choosing a Power Supply for Your Station

Are you building your first station or returning to Ham radio from a long hiatus? Unlike gear from past decades, today’s Ham radios operate on 13.8-volt power. Why 13.8V? It’s the average voltage that an automobile electrical system produces, allowing your radio to be powered in your vehicle or at home. With a few exceptions—like amplifiers—you won’t plug your gear directly into a 125V wall socket. Instead, you’ll need a good power supply to operate your station.

Linear vs. Switching

You’ll find two types of Ham-grade power supplies for sale. The linear design uses a beefy transformer to take the AC input (typically 120VAC or 240VAC) and step down the voltage, then rectify and filter the input into a DC output of 13.8 VDC. These power supplies are often large, heavy, and more expensive than switching power supplies discussed below. Many old-timers believe they are better because they’re less likely to generate RF noise.

With switching power supplies, the AC line voltage is converted directly to DC and filtered. This high-voltage DC is then fed to a power oscillator that “switches” it on and off at a rate of about 20 to 500 kHz. The result is pulsating DC that can be applied to a transformer for conversion to 13.8V. A switching power supply is also smaller, less expensive, and more efficient. Most modern versions are built to suppress possible RF noise.

How Much Power?

Power supplies are often rated by their continuous and intermittent/peak (ICS) current capacities. The figure you want to look at is the continuous rating—the amount of current the power supply can provide. For example, the Samlex SEC-1235P-M switching power supply is rated 30A continuous output, 36A peak.

If you’re running a VHF/UHF transceiver at home, especially a high-powered one, you’re going to need a significant amount of current. Typically you’ll need a minimum of 15 amps for high-power transceivers (50-80W) and at least 10 amps for medium-power radios (25-40W). Check the recommendations in your radio’s manual for specific requirements.

As you step up to HF radios with higher wattage, you’ll need larger power supplies. A transceiver with a maximum output power of 100W requires about 25A of current at 13.8V when you are operating the radio at full throttle. Again, check your manual for specific power requirements. 

Making Choices

Power supplies come in a variety of configurations, from simple to full-featured. Basic models just change 125VAC to 13VDC. Typical add-on features include volt/amp meters, multiple power outputs, noise offset controls to minimize RFI, variable voltage output controls, and over-temperature protection. DC output options available on power supplies can include Anderson Powerpoles, binding posts, set screw terminals, and lighter plugs, or combinations of these. Choose the options most useful to you.

Don’t worry about buying a power supply with a little extra current capacity. Your equipment will only draw the current it needs—no more, no less. In fact, it is probably safe to say that you can never have too much current capacity. However, if you think you’ll be upgrading to a larger radio in the near future, you may want to get the big power supply today. A 25 to 30 amp continuous rated supply is a good balance between cost and the power you’ll likely need.

Some good examples of switching supplies in the 25-30 amp range are the Samlex SEC-1235, Alinco DM-430T, and the Astron SS-30M. Astron has a good line of linear (transformer) power supplies that start at a slightly higher price point.

Accessories

If you have one radio, hookup is fairly simple. Attach the positive and negative wires from the power cord to your power supply. But if you’ve got a few more items hanging around the shack such as tuners, meters, or another radio, distribution boxes/panels will help power them all from a single supply. MFJ, SOTAbeams, Paradan, and West Mountain Radio sell a variety of these in kit or assembled form. Most use Anderson Powerpole connections.

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