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 1500transceivers 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):
www.rfspace.com
• Flex Radio systems (Flex 5000, 3000,
1500, 1000): www.flex-radio.com
• SoftRock Radio (SoftRock 40, 20, etc):
www.softrockradio.com
• HPSDR (“kit” form SDR’s): www.hpsdr.org
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.