https://aprs.fi/#!lat=51.4423&lng=6.9784 Google Maps APRS
http://websdr.ewi.utwente.nl:8901/ (Uni Twente)
https://dr2w.de/dx-propagation/
http://ham.remote-area.net/linktool
https://www.vodafone.de/hilfe/netzabdeckung
https://www.iaru-r1.org/?option=com_content&view=article&id=175&Itemid=127
https://www.circuitlab.com/user/CircuitLab/
http://db0sif.ernaehrung.uni-giessen.de