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13 Comments
- csb92376, on 10/12/2007, -0/+9I'm surprised there wasn't a mention of Amateur Radio applications in the article. In the world of amateur radio (aka "ham radio"), software defined radios ("SDR") are popping into the scene and will likely be the way radio transceivers are built in the future.
There are currently a few SDR radios on the market... namely, the SDR-1000 and a smaller experimental kit radio called the "Softrock 40". The USRP is another sdr on the market capable of being used within amateur radio spectrums.
All modern ham radio transceivers connect to computers anyway, so the connectivity between radio and computers is already there and has been for a long time. That's not the real innovation.
The real innovation here, with SDR technology, is that modulation and demodulation of radio signals is conducted via software, instead of hardware.
Traditional radio transceivers work like this : receive the signal, then pass it through another circuit that demodulates. For transceivers that can receive AM, FM, USB, LSB, CW, there are separate demodulation circuits for each mode of modulation. Then, after demodulation, the signal is usually passed through filtering and DSP (digital signal processing) circuits that clean up the signal and aid in reception of weak signals.
All that crammed into a single traditional transceiver adds up! Most amateur radio transceivers range in price from $1500 - $10,000, simply because of the complexity involved.
Enter SDR. Instead of having all these individual circuits, an SDR radio can have 1 circuit, yet be capable of everything a traditional transceiver can do. Receive the signal, downconvert it to a frequency range appropriate for digital sampling via an ADC (analog to digital converter), then perform all demodulation, filtering, DSP, etc. within software!
The USRP covered in the wired article utilizes it's own ADC chips capable of sampling wide bandwith signals, such as "wide FM" (broadcast) and HDTV.
Such chips are expensive, and thus, contributes to the $500 cost of these SDR devices.
BUT... there's another, cheaper alternative. Your computer sound card contains an ADC chip, and functions as a complete ADC device itself. The softrock-40 SDR uses your computer's sound card instead of a dedicated ADC chip.
Since a typical sound card is capable of sampling 48kilohertz of bandwith x 2 channels, a soundcard based SDR can demodulate just about anything BUT HDTV and other broad-spectrum signals. For amateur radio applications, a sound card is more than enough.- kokobaroko, on 10/12/2007, -0/+2or you can use extremly cheap 448 KHz ADC made from old $10 conexant Bt878A TV card
http://www.domenech.org/bt878a-adc/index-decimator-e.htm
- kokobaroko, on 10/12/2007, -0/+2or you can use extremly cheap 448 KHz ADC made from old $10 conexant Bt878A TV card
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