Tag Archives: SDR Reviews

The AirSpy HF+ Discovery and a new era of portable SDR DXing

The following article first appeared in the January 2020 issue of The Spectrum Monitor magazine.

The AirSpy HF+ Discovery and a new era of portable DXing

I admit it: I used to be a bit of an old-fashioned radio curmudgeon. One of those, “I like my radios with knobs and buttons” likely followed by, “…and no other way!”

However, about fifteen years ago, many of my DXing friends started turning to the world of software defined radios (or in common parlance, “SDRs”). I staunchly opposed ever following in their footsteps. One of the reasons I for this––a good one––is that, since I spend the bulk of my day in front of a computer, why would I ever want to use a computer when I’m playing radio?

But then…gradually, I found myself playing around with a few SDRs. And I quickly learned that third-generation SDRs were capable of doing something very impressive (and fun), indeed:  making spectrum recordings.  Using this tool, I found I could record not only the audio of one individual signal, but the audio of entire swathes of radio spectrum.  And even more impressive, I learned that you could later load or “play back” the spectrum recording and tune through the bands as if in real time. Any time you want. Before long, I was hooked: SDRs had become my portal into radio time travel!

I quickly found that I loved many of the other advantages of using an SDR, as well, including visual ones––like the ability to view spectrum. The interactive interface allows one to actually see radio signals across the band in real time. I also found incredible value in waterfall displays, which show signals changing in amplitude and frequency over time. Cool stuff.

I purchased my first dedicated SDR in 2012, a WinRadio Excalibur. It was––and still is––a benchmark receiver, performing circles around my tabletop receivers and general coverage transceivers.

And today, although I own and love a number of legacy radios and still listen to them in the good old-fashioned manner to which I became accustomed, I find I’m now spending the bulk of my time DXing with SDRs.

And then, more recently, two amazing things happened in the world of SDRs. Strong market competition, together with serious innovations, have come into play. Thus, for less than $200 US, you can now purchase an SDR that would have easily cost $1,000 US only ten years ago. And now, in many cases, the $200 SDR of today will outperform the $1,000 SDR of yesteryear. We are, indeed, living in good times.

And now––no more a radio curmudgeon––I’m comfortable with my SDR-user status and time at the computer, and glad I was just curious enough about SDRs to let them into my radio (and computer) world.

Portable SDRs

Since I initially dived into the world of SDRs, I’ve tried to think of a way to take them into the field.

But first, let’s get an obvious question out of the way:

Why would you want to drag an SDR into the field, when a traditional battery-powered radio is so much easier to manage?

After all, you may say, portable and even mobile tabletop receivers require no computer, no hard drive, and are likely more reliable because there are less components to manage or to cause problems for you.

In answer, let’s look at a few scenarios where heading to the field with an SDR system might just make sense.  (Hint: Many of these reasons are rooted in the SDR’s ability to record spectrum).

Good Reason #1:  Your home location is not ideal for playing radio.

Photo by Henry Be

My good friend, London Shortwave, lives in the middle of London, England. He’s an avid radio enthusiast and DXer, but his apartment is almost a perfect storm of radio interference. Listening from his home is challenging, to say the least: he can only use indoor antennas and RFI/QRM simply inundated his local airwaves.

Many years ago, he discovered that the best way to DX was to go to an area that put urban noise and radio interference at a distance.  He found that by visiting large local parks, he could play radio with almost no RFI.

Being a computer guru, he started working on a portable SDR setup so that he could go to a park, set up an antenna, and record radio spectrum while he read a book.  His systems evolved with time, each iteration being more compact less conspicuous that the previous. Later, he could head back home, open the recorded spectrum files, and tune through these “time-shifted” recordings in the comfort of his flat. This allowed London Shortwave to maximize the low-RFI listening experience by reliving the time in the park.

Over the years, he tweaked and adapted his setup, often writing his own code to make small tablets and portable computers purpose-built portable-spectrum-capture devices. If you’re curious, you might like to read about the evolution of his systems on his blog.

Clearly, for London Shortwave, an SDR is the right way to capture spectrum and thus likely the best solution for his DX listening.

Good Reason #2:  Weak-signal workarounds.

Typically radio enthusiasts turn to field operation to work in a lower-noise environment and/or where there are no antenna restrictions, often to log new stations and DX.

SDRs afford the DXer top-shelf tools for digging weak signals out of the muck. SDR applications have advanced tools for tweaking AGC settings, synchronous detectors, filters, noise reduction, and even to tailor audio.

The WinRadio Excalibur application even includes a waterfall display which represents the entire HF band (selectable 30 MHz or 50 MHz in width)

On top of that, being able to see a swath of spectrum and waterfall gives one an easier way––a visual way––to pinpoint weak or intermittent signals. This is much harder to do with a legacy radio.

Case in point:  I like listening to pirate radio stations on shortwave. With a spectrum display, I can see when a new station may be tuning up on the band so can position the receiver to listen in from the beginning of the broadcast, and never miss a beat.

Or, in another example, the visual aspect of spectrum display means I can easily locate trans-Atlantic DX on the mediumwave bands by looking for carrier peaks on the spectrum display outside the standard North American 10 kHz spacing. The signals are very easy to spot.

Good Reason #3: DXpeditions both small and large.

Mark Fahey, scanning the bands with his WinRadio Excalibur/Surface Pro 2 combo at our 2015 PARI DXpedition

Whether you’re joining an organized DXpedition or you’re simply enjoying a little vacation DXpedition, SDRs allow you to make the most of your radio time.

Indeed, most of the organized DXpedition these days heavily incorporate the use of SDRs specifically so DXers can record spectrum. Much like example #1 above, doing this allows you to enjoy the noise-free optimal conditions over and over again through spectrum recordings. Most DXpeditioners will have an SDR making recordings while they use another receiver to DX in real time. Later, they take the recording home and dig even more weak signals out of the mix: ones that might have otherwise gone unnoticed.

Good Reason #4: Sharing the spectrum with like-minded listeners.

Earlier this year, Mark gave me this 8TB hard drive chock-full of spectrum recordings.

One of the joys I’ve discovered  in making field spectrum recordings is sharing them with fellow DXers. Most of the time when I go to shortwave radio gatherings (like the Winter SWL Fest), I take a couple hard drives to exchange with other SDR enthusiasts. My friend, Mark Fahey, and I have exchanged some of our favorite spectrum recordings this way. I give him a hard drive chock-full of terabytes of recordings, and he reciprocates. Back home (or on the train or airplane) I open one of his recordings and, boom! there I am in his shack in Freeman’s Reach, Australia, tuning through Pacific stations that are not easily heard here in North America, maybe even turning up some gems Mark himself may have overlooked…just as he is doing with my recordings from the southeast US.

I’ve also acquired DXpedition spectrum recordings this way. It’s great fun to “be there” through the recordings and to enjoy some of the benefits of being on the DXpedition in times when I couldn’t actually make it there in person. For a DXer with a consuming job, busy family life, or maybe health problems that limit their travel, an SDR recording is the way to go.

Good Reason #5: Family time

Photo by David Straight

I’m a husband and father, and no matter how much I like to play radio when we’re on vacation, my family comes first, and our family activities take priority.

Having a field-portable SDR setup means that I can arrange a “set it and forget it” spectrum capture device. Before we head out the door for a family visit, tour of the area, or a hike, I simply set my SDR to record spectrum, then listen to what I “caught” after I return, or after I’m home from vacation.

This practice has allowed me to enjoy radio as much as I like, without interrupting our family adventures. Can’t beat it!

Past challenges

With all of these benefits, one might wonder why many other DXers  haven’t been using portable SDRs in the field for a while now? That’s a good question.


The WinRadio G31DDC, like many SDRs of the era, has separate data and power ports

In prior years, DXers and listeners might have been reluctant to lug an SDR and its requisite apparatus out with them. After all, it’s only been in the past decade or so that SDRs haven’t required a separate custom power supply; some legacy SDRs either required an odd voltage, or as with my WinRadio Excalibur, have very tight voltage tolerances.

Originally, taking an SDR to the field––especially in places without grid mains power––usually meant you also had to take a pricey pure sine wave inverter as well as a battery with enough capacity to run the SDR for hours on end.

Having spent many months in an off-grid cabin on the east coast of Prince Edward Island, Canada, I can confidently say it’s an ideal spot for DXing: I can erect large wire antennas there, it’s on salt water, and there are literally no locally-generated man-man noises to spoil my fun.  Of course, anytime we go to the cottage, I record spectrum, too, as this is truly a honey of a listening spot.

The view from our off-grid cabin on PEI.

The first year I took an SDR to the cabin, I made a newbie mistake:  it never dawned on me until I arrived and began to put it to use that my Goal Zero portable battery pack didn’t have a pure sine wave inverter; rather, I found it had a modified sine wave inverter built into it. The inverter could easily power my SDR, sure, but it also injected incredibly strong, unavoidable broadband noise into the mix. It rendered my whole setup absolutely useless. I gave up on the SDR on that trip.

Both the Airspy HF+ (top) and FDM-S2 (bottom) use a USB connection for both data transfer and power. Photo by Guy Atkins.

Today, most SDRs actually derive their power from a computer or laptop through a USB cable, one that doubles as a data and power cable. This effectively eliminates the need for a separate power system and inverter.

Of course, your laptop or tablet will need a means of recharging in the field because the attached SDR will drain its battery a little faster. Nowadays it’s possible to find any number of portable power packs/banks and/or DC battery sources to power laptops or tablets, as long as one is cautious that the system doesn’t inject noise. This still requires a little trial and error, but it’s much easier to remedy than having two separate power sources.

Portable computers

Even a Raspberry Pi 3B has enough horsepower to run SDR applications.

An SDR is nothing without a software application to run it. These applications, of course, require some type of computer.

I the past, SDR applications needed some computing horsepower, not necessarily to run the application itself, but to make spectrum recordings.  In addition, they often required extra on-board storage space to make these recordings sufficiently long to be useful.  This almost always meant lugging a full-sized laptop to the field, or else investing in a very pricey tablet with a hefty amount of internal storage to take along.

Today we’re fortunate to have a number of more portable computing devices to run SDR applications in the field: not just laptops or tablets, but mobile phones and even mini computers, like the eminently affordable $46 Raspberry Pi. While you still have to be conscious of your device’s computing horsepower, many small devices are amply equipped to do the job.


64-128 GB USB flash/thumb drives are affordable, portable storage options.

If you’re making spectrum and audio recordings in the field, you’ll need to store them somehow. Wideband spectrum recordings can use upwards of 2GB of data per minute or two.

Fortunately, even a 64GB USB flash drive can be purchased for as little as $7-10 US. This makes for quick off-loading of spectrum recordings from a device’s internal memory.

My portable SDR setup

It wasn’t until this year that all of the pieces finally came together for me so that I could enjoy a capable (and affordable!) field-portable SDR setup. Two components, in particular, made my setup a reality overnight; here’s what made the difference.

The AirSpy HF+ Discovery

Last year, AirSpy sent me a sample of their new HF+ Discovery SDR to test and evaluate. To be fully transparent, this was at no cost to me.

I set about putting the HF+ Discovery through its paces. Very soon, I reached a conclusion:  the HF+ Discovery is simply one of the best mediumwave and HF SDRs I’ve ever tested. Certainly, it’s the new benchmark for sub-$500 SDRs.

In fact, I was blown away. The diminutive HF+ Discovery even gives some of my other benchmark SDRs a proper run for their money. Performance is DX-grade and uncompromising, sporting impressive dynamic range and superb sensitivity and selectivity. The noise floor is also incredibly low. And I still can’t wrap my mind around the fact that you can purchase this SDR for just $169 US.

The HF+ Discovery compared in size to a DVD

In terms of portability, it’s in a class of its own. It’s tiny and incredibly lightweight. I evaluate and review SDRs all the time, but I’ve never known one that offers this performance in such a tiny package.

Are there any downsides to the HF+ Discovery? The only one I see––and it’s intentional––is that it has a smaller working bandwidth than many other similar SDRs at 768 kHz (although only recently, Airspy announced a firmware update that will increase bandwidth). Keep in mind, however, that the HF+ series SDRs were designed to prevent overload when in the presence of strong local signals. In fairness, that’s a compromise I’ll happily make.

Indeed, the HF+ Discovery maximum bandwidth isn’t a negative in my estimation unless I’m trying to grab the entire mediumwave band, all at once. For shortwave work, it’s fine because it can typically cover an entire broadcast band, allowing me to make useful spectrum recordings.

The HF+ Discovery is so remarkably tiny, that this little SDR, together with a passive loop antenna, can fit in one small travel pouch. Ideal.

The antennas

My homebrew NCPL antenna

Speaking of antennas, one of the primary reasons I’m evaluating the HF+ Discovery is because it has a very high dynamic range and can take advantage of simple antennas, in the form of passive wideband magnetic loop antennas, to achieve serious DX.

AirSpy president and engineer, Youssef Touil, experimented with several passive loop antenna designs and sizes until he found a few combinations ideally matched with the HF+ Discovery.

My good buddy, Vlado (N3CZ) helped me build such an antenna per Youssef’s specifications. Vlado had a length of Wireman Flexi 4XL that was ideal for this project (thanks, Vlad!). The only tricky part was penetrating the shielding and dielectric core at the bottom of the loop, then tapping into both sides of the center conductor for the balun connections.  Being Vlado, he used several lengths of heat shrink tubing to make a nice, clean, snag-free design. I’ll freely admit that, had I constructed this on my own, it wouldn’t have been nearly as elegant!

Click here for a step-by-step guide to building your own NCPL (Noise-Cancelling Passive Loop Antenna.

Youssef also sent me a (then) prototype Youloop passive loop antenna. It’s incredibly compact, made of high quality SMA-fitted coaxial cables. It can be set up in about 30 seconds and coiled to tuck into a jacket pocket.  The AirSpy-built loop has a lower loss transformer than the one in the homemade loop, which translates into a lower noise figure for the system.

Click here to read my review of the Youloop.

Let’s face it: SDR kit simply doesn’t get more portable than this.

The computer

My Microsoft Surface Go tablet on a hotel bed.

In the past, I used an inexpensive, circa 2013 mini Windows laptop with an internal SSD drive.  Everything worked beautifully, save the fact that it was challenging to power in the field and the internal capacity of the hard drive was so small (16GB less the operating system). In addition, it was a few years old, bought used, so the processor speed was quite slow.

This year, on the way back from the Huntsville Hamfest, I stopped by the Unclaimed Baggage Center in Scottsboro, Alabama. This center has a wide variety of used portable electronics at discount prices. I felt pretty lucky when I discovered a like-new condition Microsoft Surface Go tablet and keyboard with original charger for $190. The catch? The only data port on the tablet is a USB-C. But I grabbed a small USB-C to standard USB 3.0 dongle (for $2!) and took a risk that it would work with the HF+ Discovery.

Fortunately, it did! Score!

While the Surface Go is no powerhouse, it’s fast enough to run any of my SDRs and make spectrum recordings up to 2 MHz in width without stuttering. The only noise it seems to inject into the mix is a little RFI when I touch the trackpad on the attached keyboard.


One of my LiFePo batteries

The HF+ Discovery draws power from the Surface Go tablet via the USB port. With no additional power supply, the Surface Go may only power the HF+ Discovery for perhaps an hour at most. Since I like doing fully off-grid operations and needed to avoid RFI from inverters, I needed a portable power solution.

Fortunately, the Surface Go has a dedicated power port, so I immediately ordered a DC power cable with a standard car lighter plug.

At the Huntsville Hamfest I also purchased a small 12V 4.5 Ah Bioenno LiFePo battery and paired it with a compact Powerpole distribution panel kit I purchased in May at the 2019 Dayton Hamvention.

The LiFePo battery is small, lightweight, and can power the tablet /SDR combo for hours on end. Moreover, I have noticed no extra noise injected when the DC power is applied.

My HF+ Discovery-based portable SDR kit

My portable SDR kit on a hotel balcony.

Now I have this kit, I couldn’t be more pleased with it. When all of the components of my SDR system are assembled, they work harmoniously. The entire ensemble is also incredibly compact:  the loop antennas, SDR, Surface Go tablet, battery, and distribution panel all fit in a very small travel pack, perfect for the grab-and-go DX adventure.

The entire kit: SDR, cables, Youloop antenna, connectors and adapters all fit in my Red Oxx Lil’ Roy pack.

In November, I took the kit to the coast of South Carolina and had a blast doing a little mediumwave DXing from our hotel balcony. We were very fortunate in that I had two excellent spots to hang the homemade loop antenna: on the main balcony, and from the mini balcony off the master bedroom. Both spots yielded excellent results.

What impressed me most was the fact that the SDR# spectrum display and waterfall were absolutely chock-full of signals, and there was very little noise, even in the popular resort area where we were staying. I found that my portable radios struggled with some of the RFI emanating from the hotel, but the HF+ Discovery and passive loop combo did a much better job mitigating noise.

Check out the AM broadcast band on the spectrum display.

But no need to take my word for it.  If you would like to experience it first hand, why not download an actual spectrum recording I made using this setup?

All you’ll need to do is:

  1. Download the 1.7 GB (.wav formatted) spectrum file at this address
  2. Download a copy of SDR# if you don’t already have an SDR application that can read AirSpy spectrum files.
  3. Install SDR#, and run it.
  4. At the top left corner of the SDR# screen, choose “IQ File (.wav)” as the source, then point it to where you downloaded the file.
  5. Press the play button, and experience a little radio time travel!

This particular recording was made on the mediumwave band on November 17, 2019, starting at around 01:55 UTC.

My portable SDR kit capturing spectrum during a hike in Pisgah National Forest.

I’ve also taken this setup to several parks and remote outdoor locations, and truly enjoyed the freedom of taking spectrum recordings back home to dig through the signals.


I finally have a portable SDR system that allows me the flexibility to make spectrum recordings while travelling. The whole setup is compact and can easily be taken in a carry-on bag when flying.

The glory of this is, I can tune through my spectrum recordings in real time and DX when I’m back home, or even on the way back home, in the car, train, or airplane. It’s simply brilliant.

If you don’t already own an SDR, I can highly recommend the AirSpy HF+ Discovery if you’re primarily interested in HF and MW DXing. If you need a wideband SDR, I could also recommend the recently released SDRplay RSPdx, although it’s slightly heavier and larger than the AirSpy.

Thankfully, I am now an SDR enthusiast that can operate in the field, and this radio has had a lot to do with it. I’ll be logging many hours and miles with the AirSpy HF+ Discovery: its incredibly compact footprint, combined with its brilliant performance, is truly a winning combo.

Click here to check out the Airspy HF+ Discovery

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A review of the SDRplay RSPdx wideband SDR receiver

SDRplay recently announced the latest product in their line of affordable 14 bit wideband SDRs: the SDRplay RSPdx.

For over two weeks now, I’ve had an early production model of the RSPdx here in the shack operating on a beta version of the SDRuno application.

In the spirit of full disclosure, SDRplay is a long-time supporter of the SWLing Post and I have alpha- and beta-tested a number of their products in the past. This early production RSPdx was sent to me at no cost for a frank evaluation, and that’s exactly what I’ll offer here. To be clear, while I am using beta software, this is not a beta SDR, but one from a first limited production run.

And thus far, I must say, I’m impressed with the RSPdx. 


The RSPdx has been introduced as a replacement for the RSP2 and the RSP2pro receivers. It has been updated and upgraded, with a completely new front-end design.

Here are the highlighted improvements and changes:

  • Performance below 30 MHz has been enhanced when compared to the RSP2/RSP2pro.
  • Performance below 2 MHz has been substantially upgraded. Through the use of the new HDR mode, both dynamic range and selectivity have been considerably improved.
  • There is now a BNC antenna connector on antenna C position instead of a HiZ port. Both A and B antenna ports are SMA like other RSP models.

Let’s face it:  those of us interested in low-cost SDRs are spoiled for choice these days. The market is chock-full of sub-$200 SDRs, especially if you include all of the various RTL-SDR-based SDRs and knock-off brands/models one can find on eBay.

Personally, I invest in companies that support radio enthusiasts for the long haul…those that do their own designs, innovations, and production. SDRplay is one of those companies.

SDRplay’s market niche has been providing customers with affordable, high-performance wideband receivers that cover an impressive 1 kHz to 2 GHz.

Wideband coverage can come at a cost. Unless you pay big money for a commercial-grade wideband receiver, you’re going to find there’s a performance compromise somewhere across the spectrum.  On the RSP2 series, those compromises would have been most apparent on frequencies below 30 MHz.

That’s not to say HF, MW, and LW performance was poor on the RSP2 series–indeed, it was quite impressive and well-balanced; it just didn’t stack up to the likes of the similarly-priced AirSpy HF+ and HF+ Discovery, in my humble opinion. Both little Airspy SDRs have wooed DXers with their impressive dynamic range and overall ability to work weak signals in the HF portion of the spectrum.

Neither of the AirSpy HF+ models are wideband receivers, but still offer a generous range:  9 kHz to 31 MHz and from 60 to 260 MHz––about 11.5% of the frequency coverage of RSP models. (Note that the Airspy R2 and Mini do cover 24 – 1700 MHz.) For shortwave radio listeners that also want to venture into the UHF and SHF regions, a wideband SDR is still required.

It’s obvious SDRplay’s goal is to make the wideband RSPdx into a choice receiver for HF and, especially, for MW/LW DXers. But have they succeeded? Let’s dive in…


As I say in most of my SDR reviews: doing comparisons with receivers that have so many features and adjustments is never easy. In other words, we want an apples-to-apples comparison, but it can be difficult to achieve, especially with new products.

I compared the SDRplay RSPdx with the WinRadio Excalibur and Airspy HF+ Discovery. Here’s how I set up my comparisons:

The RSPdx, Excalibur, and HF+ Discovery all used the same antenna in my tests––a large, horizontal delta loop antenna, via my ELAD ASA15 amplified antenna splitter. I’ve used this antenna splitter for years and can vouch for its equitable, lab-grade distribution of signal.

The RSPdx is not in full production at time of posting, thus application options are limited. Typically, I’d load comparison SDRs in SDR Console or HDSDR and test them with identical settings as well. At present, the RSPdx is only compatible with a beta version of SDRplay’s own application, SDRuno (which will come out of beta rior to the first major production run). The benefit of using SDRuno is that you unlock the full potential of the RSPdx, plus signal and noise numbers are incredibly accurate.

For each SDR in this comparison, I used their native/OEM application to give them the best possible performance.

I also matched filter settings and made an effort to match AGC and volume settings as closely as I could.

Additionally, I resisted the temptation of comparing my RSP2 with the new RSPdx because I didn’t want to run two simultaneous instances of SDRuno on the same computer––especially considering one was in beta.

Is this comparison perfect?  Probably not, but I did the best with the time I had available. I do intend to make further comparisons in the future.

Longwave performance

Via the RSPdx’s new “HDR” mode, both dynamic range and selectivity have been considerably improved with frequencies below 2 MHz. While I’ll fully admit that I’m not much of a longwave DXer, my very first listening session with the RSPdx started in this region of the spectrum.

In fact, the first evening I put the RSPdx on the air and confirmed that I was, indeed, in HDR mode, I noticed a small carrier via the spectrum display on 171 kHz. I clicked on it and quickly discovered it was Medi 1. The signal was faint, but I could clearly ID at least one song. This truly impressed me because I believe this was the first time I had logged Medi 1 on longwave from the shack.

I didn’t connect the Excalibur at that point to see if it could also receive the faint Medi 1 signal, but I imagine it could have. I’m pretty sure this would have been outside the reach of the RSP2, however.

I tried to explore more of the longwave band, but due to local RFI (I suspect an appliance in my home), most of the LW band was inundated with noise. With that said, I did grab three of my benchmark non-directional beacons.

Obviously, the RSPdx is a capable LW receiver.  I would like to spend more time on this band once I’ve tracked down the source of my local RFI.

Mediumwave/AM performance

In the past two weeks, I’ve spent many hours with the RSPdx on mediumwave.

We’re heading into the winter months in the northern hemisphere, and that’s normally when my listening habits head south on the bands.

In short: I find the RSPdx to be quite sensitive and selective on the mediumwave bands while the HDR mode is engaged. A major improvement over its predecessor.

I primarily compared the RSPdx with my WinRadio Excalibur on mediumwave since I consider the Excalibur to be a benchmark MW receiver. And, as you’ll hear in the screencasts below, the RSPdx truly gives the Excalibur a run for its money:

740 AM – RSPdx vs. Excalibur:

860 AM – RSPdx vs. Excalibur:

Note that my horizontal delta loop antenna is omni-directional, hence the tug-of-war you hear between stations in the clips above.

In truth, I could have done more to stabilize the signal on both of these fine SDRs, but I wanted to keep the comparison as fair as possible.

You might have noticed that both were running AM sync mode. It seems the sync lock on the RSPdx may have also improved––though I would need to do a direct comparison with the RSP2 to know for sure––but in terms of stability, I still found that the WinRadio Excalibur was superior. Mind you, the Excalibur is a $900 – $1,000 receiver and has the strongest synchronous detector of any radio I’ve ever owned.


SDRplay notes on the preliminary specifications sheet that the RSPdx has been “enhanced” when compared with the RSP2 series.

And, after having spent two weeks with the RSPdx on the shortwave bands, I would say this is a bit of an understatement. For although I haven’t compared the RSPdx directly with the RSP2 yet, I do feel HF performance is substantially better than its predecessor. Indeed, in my comparisons, I often found it gave the Excalibur some serious competition. Overall, the Excalibur had an edge on the RSPdx, but the gap has closed substantially. That’s saying something.

For the comparison videos below, I also included the excellent AirSpy HF+ Discovery.

40M LSB – RSPdx vs. HF+ Discovery:

80M USB – RSPdx vs. Excalibur:

31M Broadcast – RSPdx vs. HF+ Discovery:

As you can see and hear, the RSPdx is now in the league of some of the finest HF receivers in my arsenal.

But I’m curious to know what you think after listening to these comparisons. Please comment!

Notch Filters

For those of you living in areas with DAB/DAB+ broadcasters nearby, you’ll be happy to note that the RSPdx has a DAB filter to help mitigate any potential overloading.

Also, if you live near a blowtorch mediumwave station, you’ll be quite pleased with the MW notch filter. It’s so effective at filtering out the mediumwave band, my local blowtorch on 1010 kHz is barely visible on the spectrum once the notch filter is engaged. (Note: I should add that neither the DAB nor the mediumwave notch filter was engaged during any of my previous comparisons above.) Check out the screen shots below showing the mediumwave band before and after the MW notch filter is engaged:




For those of you looking for a budget wideband SDR with solid performance below 30MHz, look no further.

For $199 US, you’re getting a quality UK-designed and manufactured SDR in a proper metal housing.  The OEM application, SDRuno, is one of my favorite SDR applications and can fully take advantage of the RSPdx’s new HDR mode. No doubt, with a little more time, most third-party SDR applications will also support the RSPdx.

Frankly, I was expecting classy mediumwave and longwave performance as this was the most touted upgrade of the RSPdx. SDRplay certainly delivered.

In my experience, SDRplay doesn’t oversell their products. Their preliminary product sheet mentioned improved performance on HF, but their press release didn’t even mention the HF upgrades. And this is where I, in particular, noticed significant improvement. Perhaps this is because I am primarily an SWLer, thus spend a larger portion of my time in the HF region.

SDRplay products also have a mature, robust SDR application via SDRuno. Day to day, I tend to use Simon Brown’s SDR Console as my primary SDR application, since it’s compatible with so many of my SDRs and also offers some of the best recording functionality for those of us who do audio and spectrum archiving. Each time I beta test or review an SDRplay SDR, however, I’m more and more impressed with SDRuno. It’s evolved from being a rather cluttered application to one with a thoughtful, cohesive user interface that’s a joy to use––a product of true iterative agility.

Indeed, after having used SDRuno exclusively these past two weeks, I believe I would consider it as my primary SDR application…if only it had audio recording in addition to spectrum recording, and could run multiple instances with multiple SDRs. Again, given a little time, I wouldn’t be surprised if some of this functionality is eventually integrated.


Since many SWLing Post readers already own an SDR, I’m sure some of you will have questions. Let’s address a few of those right now.

Question: “I have an RSP2/RSP2pro. Should I upgrade to the RSPdx?”

My recommendation: If you are a shortwave, mediumwave, or longwave DXer, I would indeed recommend upgrading to the RSPdx. If you primarily use your RSP2 series SDR on frequencies above 30 MHz and only occasionally venture below for casual listening, then I’d keep the RSP2.

Question: “I have an RSP1a. Should I upgrade to the RSPdx?”

My recommendation: If you’ve been enjoying your RSP1a and would like to take your listening/monitoring to the next level, then, yes, I would upgrade. Not only can you take advantage of the RSPdx’s enhanced performance, but the RSPdx affords you three antenna ports, and has a more robust front end.

Question: “I have an RSPduo. Should I buy the RSPdx?”

My recommendation: I’m a big fan of the RSPduo. Unless you’re a dedicated mediumwave/longwave DXer, or you’d just like to add another separate SDR to your radio arsenal, I wouldn’t rush out to buy the RSPdx.

And while I’m offering advice, I’d like to offer my standard two cents on the subject of performance optimization: a radio is only as good as its antenna! If you have a compromised antenna, invest in your antenna before upgrading your radio. You’ll be glad you did.


Happily, I can  recommend the SDRplay RSPdx without hesitation. This latest iteration of the RSP series SDR is a proper step forward in terms of performance and functionality––obviously implementing years of customer feedback.

SDRplay also has a proven track record of innovation and customer support. Their documentation, video tutorials, and community are among the best in the industry. Purchase with confidence.

Click here to check out the RSPdx at SDRplay.

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A review of the WiNRADiO WR-G31DDC “Excalibur” software defined radio (SDR)

The WinRadio WR-G31DDC “Excalibur” Software Defined Radio

I confess, I’m one of those shortwave radio listeners who has always believed the best tabletop radio is one that looks like a radio–a radio with knobs, buttons, a digital or analog display, and one sole purpose in life: to tune in the stations I want to hear. When software defined radios (SDRs) came to the market many years ago, I honestly thought I’d never use one, certainly never as my main receiver–after all, who wants to turn on a computer just to listen to the radio?

Who, indeed?  I’ve discovered that I do!

The WinRadio WR-G31DDC “Excalibur”

Over the past year, since I’ve become more and more engaged in shortwave radio audio archiving, I realized I needed to get a tool for making this a simpler, even more automated process. Clearly, I needed to find an SDR for the job. So, last year, I started the process of evaluating SDRs to find the one that would best suit my needs as a discriminating shortwave radio listener, ham radio operator, and amateur radio archivist. And since I wanted to be able to record spectrum, I needed a true SDR, not a PC-controlled IF receiver.

The Excalibur packages includes the receiver, application software CD, low-noise power supply, USB cable, SMA to BNC connector, and, an excellent user’s manual.

Several considerations steered me toward the WinRadio Excalibur over, say, the Microtelecom Perseus, the RF Space NetSDR, SDR IQ, or the QS1R Quicksilver–all models with which the Excalibur is often compared. It was a tough decision, and I’ll go into greater detail about my selection criteria in a future post on SDRs. But the overarching factor that guided my final decision–? Simply put, it was the Excalibur’s robust recording functionality.

I’m grateful to WinRadio for giving me a loaner Excalibur to evaluate over a two month period of time–at the end of which, I decided that I liked the radio so much, I purchased it from them for the same price they offered to their customers at the 2012 Dayton Hamvention.

The WinRadio Excalibur is manufactured in Australia

First impressions–and installation

When I first held the Excalibur receiver in my hands, I was a little surprised by its size–it’s a bit smaller than I expected. The radio itself is not much larger than a typical portable shortwave radio, thus, it’s quite easy to fit into a laptop case for mobile DXing. The unit itself has very few connections; just three, in fact:

  • an SMA type RF connector (WinRadio supplies an SMA to BNC adapter), for external antennas
  • a control cable port
  • a DC power supply port

On the “front” of the radio, there’s only a blue LED light (which can be controlled by the Excalibur software), and a power button.

The chassis is made of a durable transparent polymer, and inside, the receiver is protected by a metal enclosure. Frankly, it’s a pretty sleek looking piece of gear, and its footprint is small enough not to take up much space on a desktop. In fact, it resembles an external hard drive more than it does a receiver.

The Excalibur application software: a brief introduction

Allow me to begin by saying, the WinRadio Excalibur application software is very easy to install. The install package is surprisingly small–a little less than 10MB–thus it installs very quickly. In fact, if you want to check out the application for yourself, it’s a free download from WinRadio’s website. If you don’t have an Excalibur radio hooked up to your computer, the software will allow you to run in “Demo Mode,” in which you can explore settings, customization, etc.

Good news: the WinRadio Excalibur is purely “plug-and-play.” You load the application, you plug the radio into your PC, and it works.

The virtual control panel

The application software’s graphic user interface (GUI)–or as WinRadio calls it, the “virtual control panel”–has a very logical layout:

In the upper left part of the window (see screenshot below) you’ll find the frequency display and tabs for each of the three individual virtual receivers you can use within the allotted spectrum bandwidth (see above). In the middle of this section, you’ll find a tuning knob and configurable analog-styled meter. In the right portion of the upper pane, you’ll find all the mode controls, along with memory, filters, audio mixing, notch, squelch, gain, and the noise blanker.

The control panel, otherwise, is divided into three main spectrum windows:

  • The top right window displays the spectrum as seen by the currently selected virtual receiver. It’s within this window that you can tune, change the passband, visually adjust the notch filter, and even view the audio spectrum. It is, essentially, the IF spectrum–WinRadio calls this the “Demodulator Spectrum.”
  • The top left window contains the DDC spectrum, the bandwidth of which can vary anywhere from  20 kHz to 2 MHz, selectable in 21 steps. All three virtual receivers can be used simultaneously within the DDC spectrum bandwidth; in other words, if the DDC is set to a 1 MHz bandwidth between 9,200-10,200 kHz, you could listen to and/or record broadcasters on 9,580 and 9,625 kHz and 9,990 kHz.  The DDC spectrum window will show shaded areas which represent the location and bandwidth of each virtual receiver.
  • The wide lower window contains the Wideband Spectrum Scope, which, essentially, gives you a view of the entire HF spectrum from 0-30 or 0-50 MHz. I typically keep mine set to 0-30 MHz, as I rarely use the 30-50 MHz portion, and  it otherwise shrinks the wideband spectrum view to display the additional coverage. Perhaps what’s most useful about this scope is that it imparts the ability to “see” propagation conditions across the HF band.  Also, in this setting, I can switch between two antennas in order to see what portions of the HF spectrum each one best receives.

The DDC window displaying spectrum (click to enlarge)

The DDC and Wideband spectrum windows are selectable between a standard spectrum look or a waterfall display.  The waterfall has several color schemes to select from, as well. In the image above, I show a standard spectrum display for the DDC window, and the yellow waterfall display for the wideband spectrum. Unlike the Microtelecom Perseus, the Excalibur GUI is re-sizeable, meaning, it can be minimized or maximized to fill your monitor screen. Additionally, the spectrum windows can also be re-sized to your liking.

The DDC window displaying waterfall–note that there are several waterfall color schemes (click to enlarge)

Tuning in

Ease of tuning is a very important factor for an SDR–especially for someone like me, who really has an appreciation for the traditional, tactile tuning knob of a tabletop radio. Fortunately, the Excalibur is very simple to tune, and you have options in this respect, too.  While you can use your mouse pointer to “turn” the virtual tuning knob at the top of the control panel, I find using my PC’s keyboard’s up and down arrows to be even easier, and using these allows me to retain a sense of tactile control. If you have a mouse with a scroll button (which I highly recommend) you can tune with this, as well. Of course, you can also easily tune the receiver by clicking or dragging the mouse pointer within the DDC or DEM spectrum windows.

So many SDRs and IF receivers I’ve reviewed or used have some limitations with tuning. For example, the Perseus requires that you click a button to display a keypad box before you can enter a frequency directly. On the Excalibur, you simply type the number–and if you wish, you can even specify MHz or kHz by trailing with an “M” or “K.”  So, if you want to go to 15,550 kHz, you simply type “15550.” If you want 15,000 kHz (a.k.a. 15 MHz), you can simply type “15M.” No extra keypad windows to open. You can also assign frequency memory locations to your keyboard’s function keys.


Though the look-and-feel, layout, and overall usability of the Excalibur are important, the “rubber meets the road” in real receiver performance. The fact is, if you’re spending $900 US for a receiver, you want to know that you’re getting a good value.

Rest assured–with the Excalibur, you are.

I don’t often become giddy over a receiver, but I must confess…I love this Excalibur. Despite my initial hesitancy, this radio has proven itself, and thoroughly won me over. The Excalibur is, in short, the best SDR I have ever used. As far as I can tell, it runs neck-and-neck with the Microtelecom Perseus in sensitivity, selectivity, and overall receiver performance. The Perseus may have an edge with its adjustable DSP, but the Excalibur has an overall edge with its AM sync detector and flexible filter/mode controls.  This is my SDR.

By using the AMS mode and only selecting the lower side band sync, the interference seen in the upper side band is completely eliminated from the reception (click to enlarge)

AM Sync Detection (AMS mode)

The AM sync detector (AMS) on the Excalibur is nothing short of amazing. Though it can be a little slow to lock and is noticeably slow to self-adjust if a transmission drifts off-frequency, it’s a highly effective tool to cope with weak signal selective fading.

I’ve even found that adjacent signal noise (or QRM) that bleeds into the passband can be effectively and often completely eliminated by simply engaging the AMS on the sideband that is clear of the adjacent noise. This is remarkable.  For example, if you are listening to a weak signal on 15,585 kHz but a strong signal on 15,590 kHz is causing interference in the upper side band (easily seen on the spectrum scope), simply engage the AMS on the lower side band. Time and time again, I’ve found this to be even more effective than using a combination of the passband and notch filtering.

With strong signals, AMS is simply not needed most of the time. I have, however, engaged it several times while recording music (say, the Voice of Greece) to either lower noise from adjacent broadcasts, or simply to decrease the noise floor.

Automatic Gain Control (AGC)

The Excalibur’s pre-defined AGC levels of slow, medium and fast are quite effective, and easy to switch between. But if you wish, you can actually adjust the AGC yourself–controlling the attack and decay, setting the reference level and max gain to your own specifications, and even saving it as a personalized user setting. This personalized option will then appear as a selection under the pre-defined AGC settings.

Of course, you can also adjust the gain manually, but I find that I rarely need to do so.

The Excalibur’s notch filter can be adjusted by frequency and width (click to enlarge)


At first, I found using the Excalibur’s notch filter a little clumsy to use as compared with that of the Perseus. As with other mode adjustments and filters, the Excalibur employs a set of drop-down menus to adjust the notch. Initially I found it cumbersome to move the notch on top of interference by selecting the exact frequency from the drop-down menu. But as I’ve worked with the Excalibur a bit more, I find I now actually prefer the Excalibur’s method.

Here’s why.  To use the notch, you simply select the notch tab, click the engage button, and then the center frequency button. Now, by selecting the frequency drop-down menu and using the scroll wheel on your mouse, the notch will move across the passband accordingly. Once you’ve covered the interference with the notch, you can adjust its width with a drop-down menu–it can be widened up to 2 kHz, if needed.

You’ll find the notch especially valuable when listening within crowded ham bands or where the ham bands and AM broadcasters overlap, of course. Again, most of the time, I turn to the AMS for eliminating QRM on the broadcast bands.

Other features

Frankly, the Excalibur has so many features that it’s beyond the scope of my review to include them all. By and large, I find I like them all. Though I rarely need or use the squelch feature on HF, it is effective and highly adjustable. The Excalibur also has a noise blanker which I rarely need to use, since I no longer live in an area with RFI or an electric fence (though I would love reader comments on this). The noise blanker is so adjustable, I imagine there must be a modest learning curve, but it will probably pay off to master it if needed.

The Audio filters are also amazing–I use them frequently to tweak audio fidelity while making broadcast recordings with wide bandwidth. Indeed, in the Demodulation window, you can select the audio spectrum and actually move the filter threshold within the spectrum. This is a great–and highly visual–way of eliminating unwanted audio noise.

The only feature I feel like WinRadio falls short in, is its Memory. I don’t have an issue with assigning user memories–this is a quite simple process, and you can even assign key memory locations to the function buttons on your keyboard–but I don’t like the display of frequency databases like EIBI and HFCC. The scrollable window for the frequency databases is simply too small, and doesn’t contain enough information. I find that the Microtelecom Perseus’ memory display strikes the right balance–it reads the broadcast times and only displays what should be on frequency. The Bonito RadioJet (an IF receiver I recently reviewed) even has the option of displaying the broadcaster info within the spectrum display.  While this isn’t a make-or-break item for me, as I routinely check my copy of WRTH or other online sources for frequencies and schedules, I just hope WinRadio takes note, and considers enhancing this feature in a future update.


Recording, in my opinion, is where the Excalibur really shines. For many readers, the recording feature may be one of the least important. But for me, a busy dad with an active family life who enjoys recording and archiving shortwave broadcast, as well as listening at my leisure when my home is quiet, I rely on both automatic recording and spectrum recordings.

With the ability to record up to 2 MHz of bandwidth, you can easily capture an entire meter band, and play back the DCC recording later as if it were live–meaning, you can fully adjust every receiver parameter and every filter. Indeed, each of the three virtual receivers can be adjusted and filtered independently of each other, and are only limited within the bandwidth of the captured spectrum.

One glance at the wideband spectrum display–in the lower portion of the display– will tell you what meter bands the current propagation conditions favor (click to enlarge)

I often use this recording method to capture late-night openings or broadcasts I might miss while sleeping or away from home. I have even recorded the entire medium wave band throughout the night, then listened later for late-night trans-Atlantic DX.

Capturing large chunks of spectrum, however, is not for the hard drive-challenged. A 2 MHz recording could easily use up 100 GB of hard drive space per hour (depending on other factors, like your demodulator filter length). In reality, though, there’s never really a need to capture that much spectrum at once.

You can also make a basic audio recording within a virtual receiver without recording the spectrum. This is an important feature that the Perseus lacks–it can only record spectrum. You can actually schedule the Excalibur to record broadcasts automatically–it even allows you to set the bandwidth, mode, and other parameters you prefer.

If I want to record something particularly important, like a one-time event on one frequency, I record the spectrum at 20 kHz wide. This does not take up much hard drive space and allows me to go back later and tweak the filters throughout the broadcast (say, if QRM appears halfway through).

Again, the remarkable recording functionality of this SDR is truly what prompted me to pull the trigger on the Excalibur over other similarly-priced SDRs.

Owner’s manual

I generally find that manufacturers give very little thought to writing a proper owner’s manual.  In fact, perhaps some of the worst culprits are manufacturers of SDRs and PC-controlled radios: instead of including a printed, informative, and edited owner’s manual, they opt for either online discussion boards, or inadequate built-in/online FAQs and help databases.

Thankfully, WinRadio bucks this trend!  I am very impressed with their English owner’s manual. While the Excalibur and its software are fairly intuitive, the owner’s manual explains very thoroughly how the Excalibur works, how to tweak settings, how to customize the interface and function keys, and how to troubleshoot simple problems. I have learned a lot by simply reading the manual from cover to cover. I hope other receiver manufacturers take a note from WinRadio’s book, and follow suit.

At this price point, it is the least the buyer/user can expect.

Excalibur limitations

The Excalibur is not perfect, and like all radio receivers, it lacks some capabilities that may actually be deal-breakers for some.

Firstly, the Excalibur is a Windows (XP/Vista/7) only device. You cannot use the Excalibur with Mac OS X, Linux, or Free BSD operating systems, unless (as with some Mac OS X devices) you can run the Excalibur application within a Windows partition. Many other SDRs, noting the RF Space line, can be used with a variety of open-source SDR applications. As the name implies, with WinRadio, you’re stuck with Windows.

Also, unlike the Perseus and NetSDR, the Excalibur cannot be networked over the internet. While it may be possible to use a remote desktop application to control the Excalibur, the Excalibur application does not allow for native remote operation. By contrast, the Perseus makes this quite easy–you can even find remote stations via a dedicated server.

The lock icon on RX2 indicates that this receiver is locked, however, the frequency is not locked. One touch of the tuning knob, or one click a spectrum window can move the receiver off frequency.

This may be a personal preference, but I find the tuning lock function is a bit misleading. It does, effectively, lock a virtual receiver on frequency so that the DDC spectrum swatch can’t be moved beyond that frequency.  It does not, however, prevent one from accidentally moving the frequency within the virtual receiver. In other words, it does not “lock” the frequency as other receiver locks do.

Finally, I wish the Excalibur software would embed UTC time code into recorded DDC-captured spectrum. I got used to this feature while testing the Microtelecom Perseus, and find it a very useful. While going back through recorded spectrum, I could see the actual time passing in the spectrum. When I asked WinRadio about this feature, they didn’t say that this will/could be added to the Excalibur, but they pointed to the fact that their new Excalibur Pro’s application embeds time code.  Yet I wish they could sneak this feature into a future WR-G31DDC software update…(Are you listening, WinRadio?)


When I begin a radio review, I keep a checklist of pros and cons as I discover them to remind myself of my initial discoveries.

Here’s my list from the WinRadio Excalibur:


  • Top-class receiver in every respect—especially at a price point below $1,000 US
    • Superb sensitivity
    • Superb selectivity and adjacent signal rejection
    • Effective, visual notch-filtering
    • Effective pass band control
    • Amazing sync detector with switchable sidebands
    • Highly customizable RF gain and noise blanker (see con)
  • Spectrum/waterfall displays are responsive on my 2 year old laptop (see con)
  • Graphic user interface is
    • stable,
    • somewhat customizable,
    • intuitively designed,
    • and resizable
  • Three virtual receivers can be used independently within a max 2 MHz spectrum
  • Superior recording functionality
    • From 20 kHz up to 2 MHz of spectrum recording with 21 levels selectable
    • All three virtual receivers can record independently and simultaneously
    • Programmable recording with built-in scheduler
  • Wideband spectrum display shows 0-30 or 0-50 MHz of live spectrum
  • Simple DRM implementation which has been well-reviewed elsewhere
  • Extensive, programmable keyboard shortcuts
  • Direct frequency entry from keyboard number pad
  • Small footprint and sleek design even blends in with home office peripherals
  • Excellent, well-written proper owner’s manual
  • Courteous and responsive WinRadio customer service


  • Windows only–not available on Mac OS X or Linux operating systems
  • WinRadio GUI cannot be easily replaced with an open source GUI (see pro)
  • When recording spectrum, time code is not embedded in the waterfall display as with the Perseus and other SDRs
  • Not natively networkable (like the Perseus and RFSpace NET SDR)
  • RF gain and noise blanker are slightly complicated to tweak (see pro)
  • Lock feature does not lock tuning, it only limits DDC spectrum movement
  • A 2 GHz dual core CPU is the minimum system requirement.  In truth, I’ve found that a much faster PC is needed if you want to avoid stuttering in wide (1 MHz +) spectrum playback. Extra RAM will also help


If you’re in the market for a high-performance software defined Windows-based receiver, I suggest you seriously consider the WinRadio WR-G31DDC Excalibur.

It is, quite simply, the best SDR I have used to-date. And if, like me, recording functionality is a high-priority, then the Excalibur is your best choice, hands-down.

I’ve been using the Excalibur extensively since June 2012 to make recordings of broadcasts, many of which have been posted on the SWLing Post (check out a few).

Again, though WinRadio was kind enough to loan me the Excalibur for review on the SWLing Post, I put my money where my mouth is, and purchased it from them. Honestly, I can’t imagine my radio shack without it, now. Though I still love my traditional analog and digital tabletop radios, the Excalibur has proven to be not only an excellent tool, but also a superb receiver.

If you are an Excalibur owner, or have any comments/questions, please leave them in the comments section below.

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