Friday, October 05, 2012

Flex 5000 Diary - SDR Explained

A software-defined radio system, or SDR, is a radio communication system where components that have been typically implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded system.[1] While the concept of SDR is not new, the rapidly evolving capabilities of digital electronics render practical many processes which used to be only theoretically possible.

A basic SDR system may consist of a personal computer equipped with a sound card, or other analog-to-digital converter, preceded by some form of RF front end. Significant amounts of signal processing are handed over to the general-purpose processor, rather than being done in special-purpose hardware. Such a design produces a radio which can receive and transmit widely different radio protocols (sometimes referred to as waveforms) based solely on the software used.

Now that I have a software defined radio (SDR) ordered and en-route I plan to document everything as much as possible for my own benefit, and possibly others who may stumble onto these pages.

As the description above states SDR is a new generation of radio where a large portion of the electronic hardware formerly embedded into a receiver or transceiver is built in software and run on a personal computer.

This is overly simplistic, but think of it as a traditional radio transceiver chopped in two.
  • The first half is a box that contains just the essential electronic pieces of a traditional radio (for simplification let's say it's the power supply, receiver and transmitter).
  • The second half of the radio is your personal computer running a software package that emulates all the other pieces of a traditional radio that are now missing from the first half (filters, signal processing, control interface, etc). 
  • With a high speed digital connection cable between the two halves (Firewire, USB, or ethernet), we now have a complete radio again.
The Advantages of a SDR?
  • The first half of the radio can be simplied and the quality of the components can be increased because the overall cost of the hardware is now much lower. You can spend your development money on building a better receiver and trasmitter.
  • Personal computers have tons of processing power, way more then the embedded chips used in radios for filters, dsp, etc. Your home pc or laptop is able to beef up the speed and flexibility of it's half of the radio due to sheer processing power. 
  • Display and control of the radio is done on your computer screen. The bigger the screen (or screens) the bigger the interface and options.
  • Display modes, with a click of the mouse you have many different ways of viewing the signals and the entire band. 
  • Software is easily and quickly upgradeable. With every new version of the software new filters, better DSP, and improvements to the radio control interface can be released. Your SDR get's better and better with time as long a software development continues.
  • Digital, digital, digital. Even when integrating with other software applications for digital modes, CW, etc you can exchange audio back and forth in digital with little or no quality lost.
The Cons of SDR?
  • You need a PC or Laptop of decent performance to run your radio, it just won't work without it.
  • An unstable computer can result in an unstable radio. Nobody would of thought that their HF rig could suffer from a Blue Screen of Death (ha ha).
  • Power Consumption, a personal computer, monitors, SDR radio and power supply draw way more hydro then a traditional transceiver running off a 12v power supply.
  • In an emergency you have to keep the computer and radio running to have communications.

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