why do ham radios only have a dc power imput?

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Question by videogamer1988: why do ham radios only have a dc power imput?
They seem to all come with DC power only (negative and positive leads)

why don't they have an AC adapter plug (aka those power brick type power cables) that converts the 120VAC/ into DC (approx. 12VDC)?

Best answer:

Answer by Sullivan
An easy answer is that this permits them to be run from a car, but of course you can do that with a lot of equipment that comes with a "power brick" too... so that's not it.

It's a question of power and noise.

The radios you're talking about need a lot of power - in the range of several hundred watts input... 13.6 volts at tens of amps.

The "power bricks" you're talking about are of the "switch mode power supply" (SMPS) type. SMPS's are very small and light for a given power output, and are very efficient (i.e. they run cool). But it is generally a bad idea to run very sensitive radio receivers from SMPS. The "switching" (really "oscillating") circuits in the supply generate RF hash that can cover the desired signal in the radio.

The output of an old-style "linear" power supply (one that runs at the line frequency) is much cleaner. Unfortunately, a linear supply for the required output is much larger, heavier, and puts out a lot more heat - but we really don't have a choice.

So the supply is in a separate box (that you can put under your desk or whatever). This gets the heat and bulk and weight of the supply (which would be considerable) out of the actual radio, so the radio takes less space on your desk and can be moved around more easily. Since the supply is physically large it's in its own box, NOT generally as a "power brick."

Note that when manufacturers or retail stores quote the price of a new ham radio, it is generally NOT going to include the power supply. You have to add that. But once you have a big hefty 12V supply you can usually use it for your next radio too.

You actually can buy SMPS intended for use with ham radios. They have to be specially designed to emit very low RF noise. They're smaller, lighter, cooler, and much cheaper than linear supplies with equivalent output. But they are not yet generally accepted as "just as good" by the ham community.

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