By Jock Elliott, KB2GOM
It is hard to imagine a less spectacular looking piece of radio gear than the SDRplay RSPdx. It is literally a black box. Aside from the printing on top of the box, the most exciting thing about the RSPdx are the two red plastic covers on the antenna connectors on the side. There are no switches, no knobs . . . you can’t do anything to it except connect an antenna (or antennas) on one side and a USB cable on the opposite.
But once you connect the USB cable to your laptop and fire up the SDRuno software (that you have previously downloaded and installed), you are now in command of a listening post that covers from 1 kHz to 2 GHz.
We’ll get to the important stuff in just a minute, but first a little background.
For an oldster retrocrank like me, a proper radio has knobs and switches . . . preferably a knob or switch for every job. Lately, however, I have noticed that a lot of DXers and ordinary listeners are reporting good success with SDRs – software-defined radios. So I started to wonder about them.
There are three elements to a software-defined radio like the SDRplay RSPdx: the SDR box itself, which is the part of the system that actually receives the radio signals; a Windows computer (laptop or desktop), which provides the command and control for the SDR; and whatever antennas are required to receive the signals that the listener would like to hear. And, just to be absolutely clear, you need all three elements for the SDR system to work at all.
With my curiosity about SDRs rising, I inquired of Thomas, SWLing’s Maximum Leader, whether SDRplay – one of SWLing Post’s sponsors – might like me to take a look at one of their SDRs. Their answer was an emphatic Yes, and I had an RSPdx in my hands just a couple of days later at no cost to me or the SWLing Post.
I have to admit I had some trepidation about the process of bringing the RSPdx online because any time you have three different elements from three different sources that must work together for a system to function properly, there is always the possibility that some of the elements might not “play well together.”
Installation is easy and fast. Connect the RSPdx to the computer using a USB A-male to B-male cable (which the user must supply; often called a printer cable), then connect the antennas using the appropriate cable. In my case, I connected an MFJ 1886 Receive Loop to the Antenna C connector and an off-center fed dipole to the Antenna A connector.
To SDRplay’s great credit, they have produced an excellent video for first-timers and folks not familiar with SDRs — https://youtu.be/Oj_-dOLVzH8 . I recommend watching it, perhaps a couple of times, before you get started.
When you first fire up the SDRuno software, you will see the main panel:
And that’s when I began hearing choppy, intermittent audio. I contacted SDRplay tech support via email, and – they were working over the weekend – we got it sorted out. The problem was my five-year-old laptop, which was basically “gasping for air.”
Guided by SDRplay’s tech support, I changed some settings on the computer (including selecting windows options for maximum performance and battery management for maximum performance), a couple on the SDRuno software, and the entire system now functions flawlessly.
To use a metaphor, if you conceive of a conventional shortwave receiver as treasure map which you use to search for hidden on-the-air treasures, the RSPdx is like ground-penetrating radar. Instead of seeking active stations by tuning across the spectrum, you can see all the active signals in a band displayed as peaks. Just use your cursor to float the indicator line over the peak you want, click, and you’re there. Move your cursor to another peak, click, and you’re there. It’s quick and easy, slick and fast, and the audio coming through my headphones was very, very satisfactory.
Want a different band? Just click on one of the band buttons on receive panel. Want the upper or lower ham bands? Just click on the BANDS button with the red stripes. Suppose you click on a peak, and you are not exactly on frequency. No problem; hover the mouse over any individual digit on the frequency readout and use the scroll wheel the increment or decrement the frequency by that amount. Neat and helpful, especially when tuning a single-sideband signal.
After the RSPdx was operating properly, I spent a lot of time hopping from one shortwave band to another and was surprised that there are a lot more shortwave stations on the air than I originally thought.
Another discovery was that the SDR could be used to evaluate antennas. For example, here is the MFJ 1886 Receive Loop on medium wave as it was hanging flat against my window:
I don’t have any instruments for measuring sensitivity and other receiver performance parameters, but my sense (after comparison with some of my other receivers) is that the RSPdx is a very high-performance receiver, capable of running with the big dogs. Connect it to an antenna like the MFJ receive loop (mine is mounted indoors), and you have a very capable radio monitoring post. Highly recommended.
That’s my story, and I’m sticking to it.
Additional: the SDRplay RSPdx offers a number of very sophisticated capabilities – like recording, scanning, and so forth – and I hope to give you my report on them at some time in the future.