Software Defined Radios

By Aashish R

What is SDR? SDR-Software Defined Radio is a

general term referring to any radio design that uses a computer and some controlling software to “define” that radio’s operation.

A true SDR has very little hardware and virtually every aspect of its operation is performed by the controlling software.

SDR defines a collection of hardware and software technologies where some or all of the radio’s operating functions (also referred to as physical layer processing) are implemented through modifiable software or firmware operating on

Insight into SDR

So, what makes it work? It uses the latest in DSP technology to make a receiver (only) that works from 50kHz to 30MHz in “chunks” as large as 192kHz. Very few components in the unit, mostly the DSP chip.

The software defines the filters, the frequency coverage, the mode (USB, LSB, CW, FM, etc), the attenuators, etc.

So, WHY an SDR?

The biggest reason to have a Software Defined Radio is the flexibility it offers the user. Filtering can easily be changed, depending

on the needs Modes of operation can be changed to

accommodate new communications technologies

All of these functions are controlled in Software, rather than Hardware, making changes simpler (no new filters/hardware demodulators required- the code takes care of it)

Technology

SDR is a radio that has the ability to be transformed through the use of software or redefinable logic. In order to take advantage of such

digital processing, traditional analog signals must be converted to and from the digital domain. This is accomplished using analog-to-digital (ADC) and digital-to-analog (DAC) converters.

Key point to note

 The key point is that SDRs have the ability to go beyond simple single-channel, single-mode transceiver technology with the ability to change modes arbitrarily because the channel bandwidth, rate, and modulation are all flexibly determined through software.

Regardless of the means by which the radio is reconfigured, a fully implemented SDR will have the ability to navigate a wide range of frequencies with programmable channel bandwidth and modulation characteristics. The following list outlines some of the possible dynamic characteristics of an SDR: 

Channel bandwidth Data rate Modulation type Conversion gain

GOAL OF SDR

The most significant asset of SDR is versatility.  Wireless systems employ protocols that vary from

one service to another. Even in the same type of service, for example wireless fax, the protocol often differs from country to country. A single SDR set with an all-inclusive software repertoire can be used in any mode,anywhere in the world.

The ultimate goal of SDR engineers is to provide a single radio transceiver capable of playing the roles of cordless telephone, cell phone, wireless fax,wireless e-mail system, pager, wireless videoconferencing unit, wireless Web browser, Global Positioning System(GPS) unit, and other functions still in the realm of science fiction, operable from any location on the surface of the earth, and perhaps in space as well.

What fun can you have with SDR?

CHEAP AIS SHIP TRACKING .. AHHHHHHHH !!!!!! Large ships and passenger boats are required to

broadcast an identification signal containing position, course, speed, destination, and vessel dimension information to help prevent sea collisions.

This system is known as the “Automatic Identification System” (AIS)

. There are dedicated AIS receivers intended to be used on boats, or by hobbyists, but they can be expensive.

A radio scanner or the cheap rtl-sdr can be used to receive these signals, and with the help of decoding software, ship positions can be plotted on a map.

WONT BELIEVE ME ???

What Software Is Available?

LINRAD (written for Linux os) WINRAD (similar software, written for

Windows-based systems) New is SDR-IP, which will interface the

new RFSPACE radio via IP to the computer.

Here’s a Screen From WINRAD

Conclusions

It’s fun, it certainly introduces one to the latest in radio technology, for a reasonable price.