This morning, I got an e-mail from a reader who asked, “I would like you to help me understand software-defined radio (SDR) and applications for hams.”
Now, I’m in no way, shape, or form an expert on SDR. I know what SDR is—or at least I think I do—but how to explain it to a newcomer? So, the first thing I did, of course, was to do a Google search. Searching for “software defined radio for amateur radio operators” yielded 181,000 results.
The best one that I found is Software Defined Radio for Amateur Radio — An Overview. This is a slide show from a presentation give by Steve Dick, K1RF, on February 11, 2015. The first few slides give a good overview of what we mean when we say a radio is “software-defined.” Then, the presentation digs into some of the technical aspects of SDR.
The ARRL website has a page on SDR, but unfortunately, most of the links are to articles published from 1998 to 2002. this page should really be updated. It does include a few good links, though, including one to the BORES Signal Processing DSP course – Introduction to DSP.
Other good resources that I found include:
- An Introduction to HF Software-Defined Radio, by Andrew Barron, ZL3DW. This is a book on the topic in PDF form. Actually, I’m not really sure if this is a legal copy, as a print version is available on Amazon for $20.
- New to SDR?
- RTL-SDR.COM. This site is all about using DVB-T TV tuner dongles based on the RTL2832U chipset as software-defined radios. These dongles are very inexpensive and a cheap way to get into SDR.
If a beginner asked you this question, how would you respond? What are some resources that you have found useful?
I’d point people at a couple of things in addition to what you noted here.
If you just want to see what SDR can do for listening then both http://sdr.hu and http://websdr.org are good resources. There are lots of receivers with waterfall displays scattered throughout the world, and they can be fun either for straight-up listening or for remote monitoring of your own signals.
If you have one of the RTL tuner sticks, then you might be interested in GQRX from http://gqrx.dk/ or CubicSDR from http://cubicsdr.com/ – both provide you with a tuner that you can run on your own computer.
Once you have some sense for how this all works you might well be tempted to dive deeper into signal processing. GNU Radio http://gnuradio.org/ is a powerful tool, not particularly beginner friendly, but it’s worthwhile at least looking at how it works to get a sense for how these systems are put together.
There’s lots of fun to be had with SDR, but most of my experience with it is as a listener and not trying to use it to run a transmitter.
I disagree with the very first bullet in the presentation by Steve Dick, K1RF. A GUI does not make a radio “software defined”. It makes it a radio with a GUI.
The Elecraft K3, KX3, and KX3 are all SDRs, but they don’t come with a GUI. They come with knobs and buttons.
An SDR is a radio where the radio behavior is defined by software, not the user interface behavior.
In the early 1980’s, I joined a project working on software-defined demodulators for military use. Hardware for software-defined digital filtering had already been built in several places. These were the earliest kinds of SDR.
The audio CD created a market for DSP processors. At that point, “audio DSP” was already a potential, though it took a while to get to the ham market.
SDR is really quite simple. The analog RF signal is digitized before filtering or demodulation takes place. It might be digitized at baseband (KX2 and KX3), at IF (K3), or directly at RF (FlexRadio). There might be some analog pre-filtering (“roofing filters”) or analog AGC.
Can you add another mode with a firmware upgrade? Then it is a software-defined radio. Perhaps synchronous AM detection, added in K3 firmware release 3.57. Or PSK63, added in KX3 firmware release 2.38.
http://elecraft.365791.n2.nabble.com/K3-Beta-Firmware-Rev-3-57-Synchronous-AM-Detection-AM-S-misc-improvements-td3983997.html
http://www.elecraft.com/KX3/KX3_software.htm
ZL3DW has a new book (new edition?) for the same price, but with more content. The “Introduction to …” book is 75 pages. The new book is still $20, but is 308 pages. It is $8.50 for Kindle.
https://www.amazon.com/Software-Defined-Radio-Operators-Listeners/dp/1534992421/
Looking at the first page or so of the “Intro to” book, I like it.
Ahhhh. That explains why the PDF is free. Thanks!