Useful sites relating to electronics amateur radio and shortwave listining.

Inductance calculator.    http://m0ukd.com/calculators/air-cored-inductor-calculator/ Very handy for crystal sets and TRF receivers.

Shortwave Station Guide    http://www.short-wave.info/index.php  An excellent guide to which stations are transmitting and what you are likley to receive.

Radio Board Forums    http://theradioboard.com/rb/  General chit chat relating to construction and design.

Globourne Vintage Radio    http://golbornevintageradio.co.uk/forum/   As the name suggests  a forum dedicated to valve and vintage equipment.