Building an (unintentional) radio jammer

Long time ago, when I was just getting started with switch-mode DC-DC regulators my first design proved to be somewhat bad. Specifically, when I turned it on (without any load, mind you), FM radio two meters away lost reception.

Oops.

Cut power and radio reception returns. So, I managed to build an interference generator.  After some tweaking the design started behaving better, and next designs didn't produce practically any noise anymore (granted, most of the designs are fairly low-power and thus relatively easy to make quiet).

Now, what went wrong with the first one?

Being first experiment, I built it on breadboard, placing controller (with built-in switching transistor), diode and coil fairly far away from each other, thus unintentionally making a really big current loop that essentially works as an loop antenna. Typical switching regulators run at several hundred kiloherz, and with all harmonics that antenna will spew out a lot of wide-band noise, in this case enough to block out FM radio signal at around 90MHz.

Running that thing for extended periods might have earned a visit from military or civilian authorities, who in general are not very happy (putting it mildly) when you emit all kinds of garbage over all over RF spectrum.

Just placing components better reduced noise significantly, and properly designed PCB reduced emitted noise even further. Problem solved and lesson learned.