About a year ago, a friend, Kent Johansen, who designed the sensors that power the earthquake early warning system in our schools, gave me a device called a software-defined radio – SDR for short.
Although I have been fascinated by all aspects of radio all my life, I have ignored developments in this field in recent decades as I focused on my work in computer technology and physics.
When he handed me the device, I first heard the term “software-defined radio” mentioned, let alone seen.
I was completely confused. The radio, at least for me, had dials, lights, maybe even gauges, or some kind of digital display. This device had none of that. It was actually a little bigger than one of my thumbs. It had a USB plug at one end and a very small brass terminal near the other.
It was accompanied by a small antenna attached to the brass terminal. “Here you are,” Kent told me, “a complete radio that can tune from 25 MHz to almost 2 Ghz.”
So I remember thinking exactly what I was going to do with this little device? Most of my experience with radio in my teens was with radio signals below 25 MHz, namely AM radio, which centers around 1 MHz (for example, the Vancouver TEAM 1040 sports station operates at 1,040 MHz, and shortwave radio, which usually operates from about 5 MHz to 25 MHz (part of what is called RF, high frequency, bandwidth).
Frequencies above 25 MHz were unknown to me, except for the air band (108 – 137 MHz) and the FM band (88 – 108 MHz). My friend made vague hints about using the SDR to listen to the International Space Station or to signals bouncing off meteor paths, and he referred to signals from meteorological satellites.
After getting a ham license a few decades ago, I was also vaguely familiar with something called the 2-meter band (144-148 MHz), part of what is called the VHF (very high frequency) spectrum, which works from 30 to 300 MHz.
It took me a while to start experimenting with SPT. I did a lot of background reading, learning that SDR really has a military origin, as it makes it very easy to listen to wide frequencies. The basic concepts of SDRs developed in the 1970s, but became mainstream only relatively recently, when the concept was adapted for television.
My SDR key, made by NooElec, is a particularly good unit, costing under $ 30. I have found that this is a solid contractor that can be left to work for days, if not weeks, collecting data from satellites, for example (more on this aspect in a future column).
Unfortunately, as with many electronic devices, knockout models with questionable performance from many SDR brands can be found. Now I have a second SDR made by SDRplay, a model called RSP2. It is significantly more expensive than the NooElec model, but covers the entire spectrum from 0 to 2 GHz.
When I first turned on the NooElec SDR, it did nothing. I didn’t realize that I actually needed some software to reach its potential – in particular, I needed SDR software, essentially a utility that could use the schematics in the SDR itself to tune and demodulate (make audio) radio signals.
There are many versions of SDR software. Three that I find particularly good are SDRuno, SDR Console V3 and SDR # (pronounced SDR Sharp).
After releasing one of these free packages and contacting NooElec, the magic of software-defined radio became apparent. Something called a waterfall allows users to see entire stretches of the spectrum over a period of time. For example, if he watches the plane’s lane where communications come in short bursts, the user can spot frequencies where there has been activity and quickly tune in there.
When I watch FM stations, from the shapes of the waves and the waterfall I saw those that have added HD signals (you can for example hear the AM station News1130, promoting its HD presence on 96.9 FM HD2).
Where the SDR stands out from physical radios is the ability to tune a wide range of frequencies and modes. Examples include marine and aircraft communications, data signals such as ACARS and ADS-B (a form of radar system for domestic aircraft) from aircraft, television broadcasts and amateur radio broadcasts.
Through this experimental phase, I learned more about antennas and how different bands require different types of antennas, subject to another column.
In the meantime, for more information on SDR, check out the wealth of materials on RTL-SDR.com.