Microbit RRC-1258 MkII(s) Manual do Utilizador descarregar pdf (Página 14)

Software Defined Radio

by Mike Richards, G4WNC

Microprocessors have had a massive impact on just about all modern

electronics and radio is no exception. Whilst this began with the digital

control of local oscillators and noise reduction units, the technology has

now spread into the main core of the transceiver and is progressively

creeping ever closer to the antenna. In this chapter we will take a look at

SDR to see how it works and how we can make best use of it.

What is SDR?

SDR is very broad term that describes any system where software

performs one or more of the core functions of a receiver. The first

examples to make a widespread impact on amateur radio were the

excellent SoftRock receivers and transceivers that were designed and

produced by Tony Parks, KB9YIG. These comprised a relatively simple

hardware direct conversion receiver/exciter with an analogue IQ output

(more on this later). The IQ signals were fed to a standard PC

soundcard where tuning and demodulation took place. Dealing with

filtering, demodulation and final tuning in software brought about great

flexibility, as the performance and features could be completely trans-

formed with new software. It is this ability to introduce changes and

upgrades with ease that makes SDR technology so attractive. In

addition to the great flexibility offered by SDR, the use of Digital Signal

Processing (DSP) techniques facilitates the inclusion of filters and

advanced demodulation systems that would be virtually impossible with

conventional hardware circuitry.

There are three key technologies that are at the heart of SDR and

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Microbit RRC-1258 MkII(s) Manual do Utilizador Página 14