TITLE: Learning Software Defined Radio
AUTHOR: Chuck McManis
LAST UPDATE: 17-mar-2019


Marc Andreesen coined the phrase “software is eating the world.” It is a pretty compelling concept. So many things that we considered to be “hardware” or “process” have been reduced to algorithms and code. Perhaps there is no place where this is more evident than in the notion that software is “eating” the radio market.

My journey started in 2007 when I attended a talk at the Asilomar Microcomputer Workshop that was given by Matt Ettus on the then new product that Ettus Research had developed called the “universal software radio peripheral” or USRP. This gizmo was connected to a laptop via the USB port and it somehow turned radio waves into ones and zeros. What was even more fascinating was that there was a software environment called GNU Radio where you could take those ones and zeros and turn them into something recognizable, like the songs from an FM radio station. Needless to say, this blew my mind.

The only drawback was the cost, the original USRP with a the analog electronics (and we’ll get to that in an article later) to receive a given set of frequencies cost north of $2,000 and could get as high at nearly $5,000. Ouch! Talk about a rich person’s hobby. Not something one would “casually” investigate no matter how interesting.

But it did get investigated and people with more resources than I had at the time started playing with this stuff. And while I had missed the whole amateur radio aspect of it (HAMs were hooking their Sound Blasters audio cards to their computers in the late '90s and calling it “software radio”). According to this page both Antti Palosaari and Eric Fry had a hand in figuring out that a device intended to receive digital television could be used as a more generalized software defined radio. The chip involved, the RealTek RTL2382U, was inexpensive and with a driver could talk to GNU Radio. Suddenly it became possible to investigate SDR (on the recieving side) for less than $50. That was a price point that changed a lot of things.

What I’ve found is that software radio is the “high frequency” sibling of digital signal processing, that technology that gave us 56K baud modems. To understand SDR, you need to understand DSP. But once you do, it opens up an entirely new world to explore in terms of the radio spectrum. I have also noticed that are there two distinct group of people that come into this space, HAMs and radio operators and computer people.

Radio amateurs (HAMs) are familar with analog radios and the frequency bands between 2MHz (160 Meters) to the 420–450 MHz (70 Centimeters) band. They have a number of interesting modulation protocols and have contests to see how many other HAMs they can contact.

Computer people often started by wondering just how the now ubquitous WiFi networks work or wanted a wireless link to a remote computer. This is where I started looking at radio options, I wanted ways to use R/C toys infrastructure to connect my computer to the robots I was building.

No matter which direction you’ve come at this question, I’m hoping that some of these articles I’ve written will help you along your path.

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