Power supply
In 2007 I have built a replica of the lead-gel battery charger described in Funkamateur 7/2007. What makes this charger special is that it can be operated with a DC voltage of approximately 8.0 V to 16.0 V, meaning it can also be used with a 12 V car socket to charge batteries with a final charging voltage higher than 12V!
I've used one of these cheap switch-mode DC-DC converters (available on eBay for a few bucks) for my WSPR U3S transmitter. Checking the transmitted signal reveals strong spurious emissions. Hints from the QRPLabs group leads me to the cause - the DC-DC converter. Replacing it with a linear LM317 one solves the problem.