You can make SWL great again. Just add a couple of antennas to the RSPduo and press the Play button.

You enjoy shortwave listening, perhaps since you were a kid. At least, you used to enjoy it until you got swamped by neighborhood RFI. You live in a city, surrounded by all kinds of devices that jam the shortwave bands. Things like switched mode power supplies, VHDSL cable networks and internet routers. You try different antennas and various noise cancellers. Some things help, many don’t.

Over time, many of you have given up on your shortwave listening and sometimes ham radio hobbies. What with all the RF interference and antenna restrictions in many neighborhoods, you find your old hobby just too frustrating.

Good news, however. With the RSPduo and at least two antennas, you can make SWL great again. Really.

I am amazed at how quickly the RSPduo from SDRplay has become my favorite shortwave receiver. At my home location, shortwave hasn’t sounded this good for years, even with the meager solar cycle at present. My trick is connecting two different antennas to this dual tuner radio and using spatial diversity. For a demonstration, check out my recent experiments complete with videos.

You can make SWL great again by mixing signals from two independent tuners. These tuners are coherent, meaning the frequency and phase of their oscillators is synchronized together. But since the antennas are different – spaced apart and perhaps with different polarization – you take advantage of time differences in how the signals and noise arrive and mix together.

Make SWL Great Again – An Old Technique Reborn

Spatial filtering, or beamforming, has been around for decades. Originally achieved by phasing transmission lines, over the past decade you will find it’s gone digital. In RSPduo, you can change the amplitude and phase of I/Q signal mixing to increase signals and reduce noise.

Your results can be just good, or they can be really great, as shown in the picture above. For shortwave diversity reception, I normally just run the RSPduo in LIF mode with a modest sampling bandwidth. This lets me take advantage of 14 bit ADC performance.

Overall, I find it pretty easy to improve signal-to-noise by at least 10 dB, often much more. Your results will depend on your different antennas and the nature of your RFI. But if you have at least two antennas, the US$280 sticker price makes giving this receiving gem a try worthwhile. You might even be amazed.