Software Defined Radios
What is Software Defined Radio (or SDR)? Wikipedia gives a definition...
In short: an SDR is a radio with no IF, Modulator, or Demodulator stages as we generally understand those terms: a receiving RF preamp feeds directly into a (very fast) A-to-D converter, which is connected to a computer DSP/CPU to tune a signal and extract the modulated audio or data; on the transmit side, the CPU and DSP generate the modulation directly, and feed it to an RF power amp.
In the HF and ham world, it has appeared in 2 distinct phases; in use in high end amateur transceivers and receivers, and utilizing a PC as a controller, letting external software define how the SDR is addressed and utilized.
The forum for this wiki can be found here
Here are some introductory articles on SDRs from SWLing.com. These originally appeared in the Spectrum Monitor magazine;
Please see the following pages for further information;
You can find additional reviews and resources here;
SDRs that you can tune online can be found on our Live Tunable Receivers article