About this episode
Foundations of Amateur Radio
On your amateur radio journey, you'll likely discover that many transceivers run on 13.8 volt DC, give or take. For example my FT-857d requires 13.8 volt plus or minus 15 percent, with a negative ground, and a current draw of 22 ampere, more on that later.
In other words, the power supply needs to be between about 11.7 and 15.9 volts, the same voltage that runs most vehicles with some wiggle room for fluctuating alternator charging cycles.
While some radios will absolutely fit in your car, there's plenty where that just isn't the case, even though they're set-up for a 13.8 volt power supply. You might think of it as an anachronism, a few steps removed from spark gap transmitters, but there's more to the story.
Most residential power grids run on AC power, at varying voltages and frequencies between 50 and 60 Hz. Across the world there's eight different AC voltages in use between 100 and 240 volts. Some countries use more than one combination and I haven't even looked at three phase power. Perhaps 13.8 volt DC isn't looking quite as odd.
With this revelation comes the need to actually have 13.8 volt available in your shack. Converting your grid power to something you can plug your gear into requires some form of transformation, typically achieved with a power supply.
Efficient, cheap and plentiful, the switch mode power supply is the most common. Built to a price, they're also often noisy, not just the fan, but noisy from a radio emissions perspective.
Amateur radio has very sensitive receivers and as a result you can often hear, or see if you have a waterfall display, RF birdies, a sound reminiscent of a budgie whistling, every 100 kHz or so across the whole radio spectrum. Not something most other equipment cares about, so you're often left to fend for yourself in figuring out how to deal with this phenomenon.
There's plenty of filtering techniques and circuits to be found and some of them even work, but for my money, I'd spend it on a power supply that doesn't make noise in the first place.
A regulated power supply maintains a constant output voltage or current, regardless of variations in load or input voltage. An unregulated power supply can wander all over the place.
Adjustable power supplies allow you to set the voltage, amperage, or both, sometimes with knobs, sometimes using external controls.
At this point you might decide that this is all too hard and you want to do away with all this complexity and use a Sealed Lead Acid, or SLA battery, after all, that's what the 13.8 volt is based on, but then you'll need to charge it. Similarly, picking any battery technology requires some form of charging. Another word for charger is: power supply, often a switch mode one, and likely not filtered in any way that matters to you, since batteries, and for that matter solar power inverters, are unlikely to care about RF birdies.
I will make mention of linear power supplies. Wh
