SDR Presentation for Longmont Amateur Radio Club

Definitions:

Radio receiver: Device that will (1) pick RF up and (2) decode (demodulate) the (voice) information in a certain RF band.

Software defined Radio: Running a program that will act as a radio receiver.

Pro: SDR's also work very well as Spectrum Analyzers.
Pro: Waterfall Display - third dimension.
Pro: Software can be added / updated.
Con: Changes in computer technology can make hardware obsolete.

Typical Hardware1. Chunk of spectrum arrives at antenna and is filtered.2. The "Mixer". The resultant "chunk" of spectrum is fed into each of two separate switches. 3. Each of the two switches also receives one of two local oscillator signals that are identical, but are 90 degrees out off phase.4. The Chunk is Down-Converted to AF.5. The resultant baseband (AF) signals are amplified and appear at the I (In-Phase) and Q (Quadrature) outputs, identical to each other, but 90 degrees out of phase.

Typically we want to demodulate voice information and we have soundcards (ADC) built into computers - which means a lot of SDR activities revolves around sound cards.

Typical soundcards runs at 44.1 Khz or 48Khz - which means 24Khz bandwidth.
High level cards runs 96kHz and up to 192 kHz which means bandwidths up to 92 kHz.
Experiment with soundcard - Speclab and vlf.it
Antennas an issue.

Bandwidth is determined by ADC and transfer technology.