Amateur Radio (G3TXQ) - Common-mode chokes An in depth look into RF Chokes by G3TXQ.
Amateur Radio (I0QM) - 1:1 Coax Balun An insight of how to make a 1:1 Balun from coax cable.
Understanding HF Propagation VE2XIP editions Amateur Radio views and reviews for Beginners
Smith Chart Tutorial Invented by Phillip H. Smith in 1939. Tutorial papers by Frank .A.Lynch