20W Tuner 1:1 Balun Converter Adapter HF Antenna for HAM Radio Unbalanced Parts | eBay
Antenna Theory - Baluns
Nooelec - Nooelec NESDR SMArt HF Bundle: 100kHz-1.7GHz Software Defined Radio Set for HF/UHF/VHF including RTL-SDR, Assembled Ham It Up Upconverter, Balun, Adapters