Crystal Radio Supply
- Crystal Radio Kits, parts and supplies including litz wire, ferrite core and variable capacitors, plus other peripherals and components.
- http://crystalradiosupply.com

WD8DAS Sync Page
- Offers information about synchronous detection and retrofit synchronous detectors in kit and finished form.
- http://www.qsl.net/wd8das/sync.html

JPS Communications, Inc.
- JPS Communications is a manufacturer of DSP equipment for military, shortwave and ham radio applications.
- http://www.jps.com

Quantics W9GR Digital Signal Processors
- Information about the DSP-3 which removes noise and other unwanted interference from voice and data communications signals.
- http://www.w9gr.com/

Harry's Homebrew Homepage
- Extensive collection of useful receiver, antenna and peripheral homebrew projects, for ham radio and other DX hobbyists.
- http://sm0vpo.8m.com/