The Ham-It-Up upconverter uses a 5V USB power input. I discovered that different 5v power sources can cause significant interference with this upconverter, and the same effect will probably occur in other upconverters as well.
When the upconverter was powered by mains power via a phone charger, the signals were almost completely drowned out in noise. Powering it with a PC USB port was better, but the PC USB power introduced some other strong noise sources. Powering it with a battery (used a mobile phone with OTG cable) was the best option. There are still some strong noise sources present, but I can probably solve them with better shielding.
Click continue reading to see some comparison images.
Mains Power Supply (Via. Phone Charger)
PC USB Power Supply
Mobile Phone Battery Power (Via OTG Cable)