■ FIGURE 3. The C. Crane CCRadio- 2 Titanium is optimized
for AM band DXing. It has a built-in, twin-coil ferrite antenna.
The radio covers the FM band, the ham two-meter band,
and the 162 MHz weather band. Price is typically about $150.
the received signal is then sent to the processor where the
filtering and demodulation is done using special software
algorithms. The recovered digital signal is then put through
a digital-to-analog converter (DAC) and sent for
amplification to the speaker or headset.
Until recently, ADCs were not fast enough for RF
signals nor were the processors fast enough to process all
that digital data in real time. Now, we have both fast
ADCs and fast DSPs making SDR a reality. The technique
is used almost universally in cell phones but not so much
in general-purpose radios. Today, you can buy an SDR SW
or ham radio. I hadn’t tried one until recently when I
decided to buy the RFSpace SDR-IQ — a tiny SDR for ham
or SW use ( www.rfspace.com). It is still expensive ($500),
but its performance competes well against existing analog
Inside the tiny SDR-IQ in Figure 5 is an input RF
amplifier and some initial LC filters that select signals in
one of three ranges: 0 to 5 MHz; 5 MHz to 15 MHz; or
15 MHz to 30 MHz. The signals are then digitized by an
■ FIGURE 5. The RFSpace SDR-IQ software-defined radio.
It essentially covers from zero to 30 MHz. I used an MFJ
16010 antenna tuner to match the 50 ohm input of the
receiver to my long wire antenna.
■ FIGURE 4. The C. Crane CCRadio-SW has the twin-coil
ferrite antenna for AM band listening and full shortwave
coverage from 1.7 to 30 MHz. Price is also about $150.
ADC sampling at a rate of 66. 66 MHz. The resulting signal
goes to a digital downconverter that effectively selects a
190 kHz chunk of spectrum for processing. The digital
signals are then sent to a PC or laptop via the USB port
where the Pentium or Athelon processor does the fast
Fourier transform (FFT) spectrum analysis, demodulation,
and filtering. The USB port powers the entire receiver, as
well. You hear the output on your PC speakers or with a
headset. Software on the PC shows the spectrum being
received and provides on-screen buttons and controls. You
literally operate the radio with your mouse.
The screen display in Figure 6 presents amplitude vs.
frequency just like you would see on a spectrum analyzer
over a 190 kHz range. You can see all the available signals
within that range. Just click on them to hear them. The
screen can also implement a waterfall display. This is a
vertically scrolling screen (over time) and gives the
impression of a waterfall. It’s not particularly useful, but
As for performance, it appears to be as good as any
other receiver I have used and better than many. Tuning
and operating the radio does take some getting used to.
THE CRITICAL ANTENNA
Let me tell you this right up front. You will need a
good antenna if you are going to do any serious SWLing,
especially DXing. Some radios come with a built-in
telescoping whip or ferrite coil antenna. Depending on the
receiver, this may be fine. But if you really want to get the
farthest and weakest signals, a good outdoor antenna is
best. Most of my SWLing is done with a 20-30 ft wire. You
will notice significant results if you can string up 50 to 100
feet of wire outside. You can put it in the attic but it won’t
work too well if you have aluminum shielding for hot
Most SW radios have a screw or pressure terminal for
an external antenna. Some (like the SDR-IQ) only have a
BNC 50 ohm connector. I ended up buying a BNC to SO-