Databases

http://www.hardwarebook.net/
Hardware Book. Internet's largest free collection of connector pin outs and cable descriptions.

http://www.beyondlogic.org/

http://www.epanorama.net/

http://www.minicircuits.com/dg03-110.pdf
dBm-Volt-Watt Conversions

  Auxiliary Calculation Programmes

http://www.cvs1.uklinux.net/calculators/
The Electronics Calculator Website

http://www.spin.gr/static/sections/applets/index.html
Simulated laboratory with Java minor applications