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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.
Give your answer to this question below!
One answer is that a 12 volt radio is ready to run on emergency power – such as a deep cycle battery.
Or add a power supply and the same rsdio can now run off of AC power. It allows the best of both worlds – AC or DC.
Me: Ham for 25 years
A large number of base-station amateur radios
have built-in power supplies, but few of the ones that do
can be operated from external 12 V sources.
Where the power comes from matters far less
than that it is reasonably free of spikes and noise,
that it is of the right voltage,
and that sufficient current is available.
“Floor bricks” aren’t capable of delivering much current,
so only QRP-level (10 watts or less) radios
can readily be operated from them.
Radios that transmit over 20 watts or so need larger, higher-current
power supplies that cannot be conveniently contained in a floor brick;
even switching supplies that are small and lightweight for their output
need a solid chassis of some sort to be structurally stable.
Also, higher-current supplies need very good ventilation,
which is not a particularly salient feature of floor bricks.
The use of separate power supplies is nothing new:
Back in the tube days, using a separate power supply
was quite normal, as it was unavoidably very large,
and the transformers and chokes used were very heavy.
Some of these supplies weighed upwards of 75 pounds.
Aside from all that, most modern amateur radios
are equipped for 12 V operation for practical reasons:
Amateur radio is vital during emergencies,
many of which involve widespread power outages.
Radios that operate on 12 V can be connected to either a vehicle
or a standalone battery almost at a moment’s notice.
This allows their owners to get on the air quickly
even when there is no AC available.
As with many other matters, it all makes a lot more sense
when you know enough about it.
[Caution: The previous sentence cannot be relied on
when you are dealing with any government.]
73
KJ6QKV
[Answer supplied from the U.S. via Y!A Canada
to circumvent the new, unusable version.]
Because most are designed to be installed in a vehicle.