A Beginner’s Guide To Software Defined Radios By Dave Hallidy K2DH 3/2010

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. Most of today’s ham rigs incorporate at least some level of software definition of their operational modes. A true SDR has very little hardware and virtually every aspect of its operation is performed by the controlling software.

The SDR-IQ 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 (SpectraVue from the mfr, lots of other stuff out there) defines the filters, the frequency coverage, the mode (USB, LSB, CW, FM, etc), the attenuators, etc.

Some Of The SDR’s On The Market Flex Radio- the Flex 5000, 3000, 1000 and now transceivers with varying levels of sophistication. RFSpace- SDR-IQ, SDR-14- receivers with superior performance and features. SoftRoc- Simple, small single-band receivers offering a great intro into SDR’s for $20-$50. HPSDR- transceivers offering varying levels of sophistication and features, depending on what options are purchased and how the builder configures them. Numerous others; do a Google search on SDR for a surprisingly long list. Also refer to QST, there have been a number of reviews of them.

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)

So, WHY an SDR? (cont’d) One of the biggest features is the ability to “look at” or view a chunk of the radio spectrum, all frequencies at the same time, to find stations or places to operate. The SDR-IQ can look at as much as 192kHz of the spectrum at any time, making the unit a useful “Panadaptor”, when connected to the station antenna. Using the supplied software, it can also be used to control the “real” station transceiver when selecting stations to work. SDR’s can also output the recovered signals to a PC and thus, chunks of spectrum can be stored as.wav files and replayed later for analysis.

Links to some SDR Suppliers RFSPACE (SDR-IQ, SDR-14): Flex Radio systems (Flex 5000, 3000, 1500, 1000): SoftRock Radio (SoftRock 40, 20, etc): HPSDR (“kit” form SDR’s):

What Software Is Available? There is quite a bit out there, more being written every day. In addition to the software supplied with the various radios, two very good programs are: LINRAD (written for Linux os) and WINRAD (similar software, written for Windows-based systems). New is SDR-IP, which will interface the new RFSPACE radio via IP to the computer. There is plenty of good code out there for users of the Flex radios, the SoftRock’s, and the HPSDR’s, enabling many new modes and functions. I suggest joining one or more of the SDR forums for the latest info and evaluations of software.

So Let’s Look At A Receiver Screen Using Spectravue

And Another

Here’s a Screen From WINRAD

So- Can We Run This Thing? Yes! I’ve recorded some “chunks” of the HF Spectrum during the recent ARRL DX Phone contest, for playback here. Also a bit of the low end of 20m CW. You can tune through the recorded spectrum just as if you were tuning a receiver “live” on the band, tuning individual signals and analyzing them. Try it!

Why I Bought The SDR-IQ Frankly, my intent was NOT to record the HF spectrum and analyze signals. I wanted a really good “Panadaptor” to connect to my 1296 EME receiver (which happens to downconvert to 28MHz). I felt this would help me find stations to work off the moon, as I could look at up to 192kHz of the 1296 band at any time, find a station, click on it, and listen to it. I’ve not had a lot of time to play with this function yet, but what little I have has indicated to me that this will be a superior way to find EME stations and dig them out. I can also connect the SDR to my IC-756PROII and let the SDR tune the PRO to the stations I’ve found and want to work.

Conclusions This is just a bare beginning for me. I expect to find many more uses for the SDR in my shack- single signal spectrum analysis among them. It’s fun, it certainly introduces one to the latest in radio technology, for a reasonable price. I’ll keep you all updated as I discover more features and uses of this fine tool.