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Author Topic: What is SDR - software derived radio?  (Read 2415 times)

Offline syhprum

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What is SDR - software derived radio?
« on: 07/07/2012 09:51:31 »
SDR is a fascinating field common DVB dongles are in fact SDR receivers and some can be used to receive a wide range of frequencys with suitable software.
HDSDR software is available free of charge and is a good place to start, I have not as yet been able to receive any transmissions on my Climax dvb dongle but I am able to use the HDSDR software to transfer pre recorded NOAA files and learn how to use it.
I have a Moxon DVB dongle on order that uses an e4000 chip which I understand is one of the better ones for off the air reception.   
« Last Edit: 12/07/2012 22:05:27 by chris »


 

Offline syhprum

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Re: software derived radio
« Reply #1 on: 11/07/2012 14:59:58 »
Is no one interested in SDR,s I thought they were the latest thing?.
 

Offline evan_au

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Re: software derived radio
« Reply #2 on: 12/07/2012 22:15:49 »
SDR is a big new thing - an attempt to cross the Universal Turing Machine with a Crystal Set!

This will impact most consumers by having a smart phone that can access several frequency bands for faster downloads, and be able to dynamically switch between different modulation formats between home and on the road, or when entering the service area of a different carrier.

This will impact manufacturers by allowing one hardware product to be sold in multiple countries, despite their having different TV/Wireless modulation formats and different transmission bands.

The overall impact for society will probably come through cognitive radio - dynamically reusing the scarce spectrum resources, most of which is unused, in most places, most of the time.

The challenge is to get a copy of the software to decode a given format (it's usually proprietary) or write it yourself (it is large and complex) - and then to pick up a signal in the right format (the right antenna and preamplifier), and even then it will often be encrypted.

So for most people, it is easier to go to the NOAA website to get images of the weather.

SDR is not quite as universal as the computer: With the Universal Turing Machine, if it is not quite as fast as you want, you just wait a bit longer to calculate Pi to 1000 decimal places.
But decoding Wireless signals is a Real-Time process - if your SDR is not quite fast enough, it just gets further and further behind.
So there is a certain range of modulation formats that can be decoded by a given SDR chip; but the next generation of modulation formats will require even more processing power, for which you need an SDR hardware upgrade.

Perhaps there will be more interest within groups like IEEE, eg http://www.ewh.ieee.org/r6/scv/ssc/Abidi.pdf
 

Offline graham.d

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Re: What is SDR - software derived radio?
« Reply #3 on: 22/07/2012 10:48:29 »
SDR is Software Defined Radio (not Derived). It refers to the design of a radio to have its hardware adptable by software programming to make it versatile enough to be able to transmit and receive on a wide range of frequencies and with a wide range of modulation schemes. There is no universal SDR as the range of frequencies and types of modulations used are too large to encompass. Also, as you may imagine, adding universality usually comes at a cost - not just dollars but also in terms of optimising performance for any one standard.

The ideal SDR receiver takes the RF signal from a cleverly designed multiband aerial, has a very wide band Low Noise Amplifier followed by a very, very fast, high resolution, Analog to digital converter. Al  the rest of the channel selection, demudulation and decoding is then done in a very fast Digital Signal Processor. Technology is a long way from this although it can be done to a limited extent - of course this doesn't stop manufacturers using the term SDR just because of these limitations :-) Mobile phones are a good example of SDR; even if not universal they do strive to make the radio work over a wide variety of frequencies (900MHz to over 2GHz) and with quite a few modulation standards. High demand is also from the military which have receiver requirements from 30MHz to over 2GHz with an even wider range of modulations.

 

Offline syhprum

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Re: What is SDR - software derived radio?
« Reply #4 on: 25/07/2012 22:20:21 »
I have given up for the moment trying to operate a DVT dongle as a SDR as I suspect that the built in sound card on my cheap mother board is not up to the job.
I can receive nothing and it makes no difference whether the dongle is plugged in or not or whether an antenna is connected to it or not although I have tried vaious drivers.
The new Moxon dongle works fine with the software provided to receive sound broarcasts.
 

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Re: What is SDR - software derived radio?
« Reply #4 on: 25/07/2012 22:20:21 »

 

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