I bought some boosters from USB to 9 or 12 V. The idea was to power an old-ish handheld receiver so that I don't have to buy a new battery, dedicated charger and so on. Also they came with the Yaesu favorite 4.0x1.7mm plug.
The result is impressive: even at UHF the receiver goes totally deaf. Let alone in AM where the squelch won't close at any setting.
And it's not only the relatively unfiltered boosted DC: even a nearby receiver picks up the noise. Sure enough the spectrum analyzer with a rubber duckie sees the noise too!
That thing is spamming the airwaves with noise.
I suspected the output cable acts as antenna, so I tried running it with no cable and a load resistor soldered at its terminals. I can still pick up the noise on the nearby handheld receiver.
While I was fiddling inside, I reversed the simple circuit. It looks like the sample diagram from FP6291 datasheet since the pinout and components match 100%. Not much to change in there to make it better.
I tried adding a 7809 in series to the 12V output, but the noise can still be picked up.
Alright: these boosters are good for recharging a battery pack or powering LEDs when no radio is in use.
