Tag Archives: Software Defined Radio

Software Defined Radio Primer Part 1: Introduction to SDRs and SDR applications

The new ELAD FDM-S3.

The following article originally appeared in the June 2018 issue of The Spectrum Monitor magazine:


SDR Primer Part 1: Introduction to SDRs and SDR applications

I author a radio blog known as the SWLing Post; as a result, I receive radio-related queries from my readers on a daily basis.  Among the most common questions are these:

“So, what is an SDR, exactly? Are these better than regular radios?”

and/or,

“I think I’d like to buy an SDR. Which one do you recommend?”

Great questions, both! But, before I address them, I must let the reader know that they are also “loaded” questions: simple enough to ask, but quite nuanced when it comes to the answers.

No worries, though; the following three-part primer sets out to address these questions (and many more) as thoroughly as possible. This first part of the primer will focus on the basic components of an SDR system. In part two, next month, we’ll look at affordable SDRs: those costing less than $200 US. In part three, we’ll take a look at pricier models and even include a few transceivers that are based on embedded SDRs.

But before we begin, let’s start with the most basic question: What is a Software Defined Radio (SDR), exactly?

Not your grandpa’s radio

Here’s how Wikipedia defines SDR:

“Software-defined radio (SDR) is a radio communication system where components that have been traditionally implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded system.”

Whereas your grandpa’s radio was all hardware––in the form of filters, mixers, amplifiers, and the like––SDRs are a mix of hardware and software. With the exception of tabletop transceivers and receivers with embedded software and systems (which we’ll discuss in part three of our investigation), SDRs typically take on a “black box” appearance: in other words, the radio looks like a simple piece of hardware with a minimum of an antenna port, a data port and many times there’s also some sort of LED or light to let you know when the unit is in operation. On some models of SDRs, there is a separate power port, additional antenna connections, power switch, and possibly some other features; however, “black box” SDRs often look like a nondescript piece of portable computer hardware––something like an external portable hard drive.

Why would you want an SDR?

Many of us have made it through life thus far without an SDR…so, why in the world should we want the use of one?  Below, I’ll list some of the most appealing reasons:

Bang-for-buck

The Airspy HF+ (top) and FDM-S2 (bottom). Photo by Guy Atkins.

By and large, SDRs are quite a value when compared to legacy all-hardware radios. For example, I wouldn’t hesitate to pit my SDRs––such as the $500 Elad FDM-S2 or $900 WinRadio Excalibur––against legacy receivers that cost two to three times their price. Indeed, my $200 AirSpy HF+ SDR will give many DX-grade ham radio general coverage receivers a real run for their money. They’re that good.

Spectrum display

SDR applications have a spectrum display which gives you a real-time view of a broad swath of the radio dial. Whereas you can tune to and listen to one frequency at a time with legacy receivers, SDRs allow you to view, say, the entire 31 meter band. With the spectrum display, you can see when signals come on or go off the air without actually being tuned in to them. You can tell what signal might be causing interference because you can see the outline of its carrier. Spectrum displays are truly a window––a visual representation––of what’s on the radio. Using legacy receivers now often makes me feel like I’m cruising the bands with blinders on. After becoming accustomed to having a spectrum display, there’s simply no way I’d want to be without at least one SDR in my shack.

Powerful tools

I like how clean the user interface is for this SDR application (SDRuno) window that controls the SDR’s frequency, mode, filters and notch.

SDRs usually afford access to a dizzying array of customizable filters, gain controls, noise blankers, digital signal processing (DSP), audio controls, and more. Being able to customize the SDR’s performance and listening experience is simply unsurpassed. In fact, it’s almost a curse for SDR reviewers like me––comparing two SDRs is problematic because each can be altered so much that identifying the best performance characteristics of one or the other becomes a real challenge. In other words, comparing SDRs is almost like comparing apples to oranges: even using a different application can enhance and thus alter the performance characteristics of an SDR.

Multiple virtual receivers

SDR Console makes managing multiple virtual receivers a breeze.

Whereas most legacy tabletop receivers allow you to switch between two VFOs (VFO A and B) some modern SDR applications allow for multiple independent virtual receivers––in essence, multiple sub-receivers. On my WinRadio Excalibur, for example, I can run three fully-functional and independent virtual receivers within a 2 MHz span. On receiver 1, I might be recording a shortwave broadcaster on 7490 kHz. On receiver 2, I might be recording a different broadcaster on 6100 kHz, and following a 40 meter ham radio net on 7200 kHz in the lower sideband.

Recording tools

SDR applications, more often than not, have functionality for making audio recordings of what you receive. Some, like the WinRadio Excalibur and SDR Console, actually allow for multiple simultaneous recordings on all of their virtual receivers.

SDR Console recording dialog box

Most SDR applications also allow you to make spectrum recordings, that is, to record not just one individual broadcast from one radio station at a time, but to record an entire broadcast band, all at once. Each recording can easily contain dozens of stations broadcasting simultaneously. Later, you open the recording and play it back through the SDR application. Recordings can be tuned and listened to as if they were live. Indeed, to the SDR application, there is no difference in using an antenna or using a recorded spectrum file; the tuning experience to the listener is also identical.

So imagine that propagation is stellar one evening, or there’s a global pirate radio event just when you’re going to be away from home: simply trigger a spectrum recording and do a little radio time travel tuning later. It’s that easy.

Constant upgrades

Both SDR applications and SDR firmware are upgradable from most manufacturers. In fact, I’ve found that the most affordable SDRs tend to have the most frequent upgrades and updates. Updates can have a positive impact on an SDR’s performance, can add new features, such as the ability to expand the frequency range or more filters or embed time stamps in the spectrum waterfall. It could be pretty much anything and that’s what’s so brilliant. As a user you can make requests; your SDR’s developers might, if they like the idea, be able to implement it.

So, what’s not to love?

Looking at all of these advantages of SDRs over legacy radios, it sounds like SDRs should truly suit everyone. But the reality is, they don’t. For some radio enthusiasts, SDRs do have some unfortunate disadvantages:

First, if you’re primarily a Mac OS or Linux user, and/or prefer one of these platforms, you’ll find you have much less selection in terms of SDRs and applications. While there are a few good applications for each, there are many more SDR applications for PCs operating Windows. Until I moved into the world of SDRs, in fact, I was a Mac OS user outside of work. At the time, there were only one or two SDR applications that ran on the Mac OS––and neither was particularly good. I considered purchasing a copy of Windows for my MacBook, but decided to invest in a tower PC, instead.

Second, one of the great things about legacy radios is that with just a radio, a power source, and an antenna, you’re good to go; travel, field operations, and DXpeditions are quite simple and straightforward. SDRs, on the other hand, require a computer of some sort; when traveling, this is typically a laptop. I’ve spent several summers in an off-grid cabin in Prince Edward Island, Canada. My spot is superb for catching DX, and there’s no RF interference, so I love making spectrum recordings I can listen to later. Problem is, powering so many devices while off-grid is an art. Normally, my laptop can run off of battery power for hours, but when the laptop also provides power to an SDR and portable hard drive, it drains the battery two to three times faster.

The ELAD FDM-DUOr (receiver).

With this said, keep in mind that there are fully functional tabletop radios (like the Elad FDM-DUO and FDM-DUOr) that are actually SDRs, providing an easy way to bypass this concern.

Finally, there are simply some people who do not care to mix PCs and radio. I’ve a friend who’s a programmer, and when he comes home to play radio and relax, the last thing he wants to do is turn on a computer. I get it––as a former programmer, I used to feel that way myself.  But the world of SDRs lured me in…and now I’m a convert.

Scope of this primer series

The world of SDRs is the fastest growing, most dynamic aspect of the radio world. Because of this, I simply can’t include all SDRs currently on the market in this primer.  Let’s face it: there are just too many, and it is beyond the scope of this article to try to cover them all. Instead, I’ve curated my list, by no means comprehensive, to include a selection of the most popular and widely-used models.

I’ll be focusing on SDR receivers unless otherwise noted. In Part Three, I’ll call out some popular SDR transceivers. Additionally, I’ll bring my attention to bear on the “black box” variety of SDRs.

This primer is long overdue on my part, so I’ll provide answers to the most frequent questions I receive. But though this primer is in three parts, it barely scratches the surface of the vast world of SDRs.

Thus far we’ve defined an SDR and discussed its advantages and disadvantages.

Now, let’s take a closer look at what you’ll need to build a station around an SDR.

Assembling an SDR station

Guy Atkins’ laptop running HDSDR software in his SUV; the receiver is an Elad FDM-S2. (Photo: Guy Atkins)

In truth, most of you reading this primer will already have everything you need to build a listening post around an SDR. Understanding the components of the system in advance, however, will put you in a better position to get on the air quickly with an SDR that suits your needs best. Let’s discuss this component by component.

A computer

By virtue of reading this primer now being displayed on your screen, unless you’ve printed it out, I’m guessing you have access to a computer of some sort.

SDRs are really quite flexible in terms of computer requirements. SDRs are compatible with:

  • A desktop PC running the Windows operating system
  • A laptop PC running the Windows operating system
  • A desktop Apple computer running MacOS and/or Windows
  • A laptop Apple computer running MacOS and/or Windows
  • A tablet or smartphone computer running Android or Windows
  • A Raspberry Pi/Beaglebone (or similar budget computer) running a Linux distribution

If SDRs are compatible with so many computer operating systems and configurations, then why would you worry about which ones to choose?

As I mentioned earlier most, but not all, of the SDR applications on the market are only compatible with the Windows operating system. If you want the most out-of-the-box, plug-and-play SDR options, then you should plan to use a Windows PC. If you’re a MacOS user, fear not. Modern Apple computers can support Windows—you simply purchase a copy of Windows and set your system to boot as a Windows machine (assuming you have the storage space for a dual boot).

Secondly, processing speed is certainly a factor: the faster, the better. While you can use an Android/Windows tablet or a Raspberry Pi to run an SDR, they often don’t have features like multiple virtual receivers, wideband spectrum recording capabilities, and large fluid waterfall displays due to the simple lack of processing power. My guess is that by 2023, however, tablets and budget computers will have ample processing power to handle most, if not all, SDR functions.

Finally, if you plan to make spectrum recordings, especially wideband ones (2 MHz, plus), you need both a snappy processor and a high-capacity hard drive with a decent write speed. This is the reason I now have a desktop PC at home for spectrum recordings: I can use a very affordable SATA drive as a storage device, and the write speed is always more than adequate. My OS and SDR applications run on an SSD (solid state drive) which is very fast.  All of my recordings are saved to internal and external 4TB+ hard drives. Happily, I’ve never had a hiccup with this system.

An SDR application

SDRuno has an attractive user interface comprised of multiple adjustable windows.

Wait a minute…am I suggesting you choose an SDR application before you choose an SDR?  Why, yes, I am! You cannot use an SDR without an SDR application, but, with only a few exceptions, you certainly can use an SDR application without an SDR attached.

Unlike a legacy hardware radio, you can essentially test drive an SDR by downloading an application (almost always free) and then downloading a test spectrum file. Most SDR manufacturers will have all of this on their download page. Simply install the application, open the spectrum file, et voila! You’re now test driving the SDR. Your experience will be identical to the person who originally made the spectrum recording.

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

I always suggest test driving an application prior to purchasing an SDR.

While all SDR applications have their own unique layout and menu structure, almost all have the same components, as follows:

  • a spectrum display, which gives you real-time information about all of the signals within the SDR’s frequency range;
  • a waterfall display, which is a graphical representation of the signals amplitude or strength across the SDR’s frequency range displayed over time;
  • filter controls, which help you adjust both audio and signal widths;
  • mode selections, which allow you to change between modes such as AM, SSB, FM, and digital;
  • a signal meter, which is typically calibrated and resembles a traditional receiver’s “S” meter;
  • a frequency display for the active frequency;
  • VFOs/virtual receivers, which may have real estate allocated on the display;
  • a clock, which displays the time, possibly as both UTC and local time (note that many SDR apps also embed time code in waterfall display);
  • memories, where you can store a near-infinite number of frequencies (and some SDR applications allow you to import full-frequency databases); as well as
  • other controls, such as squelch, gain, noise blanker, DSP, notch,etc.

After you’ve become comfortable with one SDR application, moving to another can be a little disorienting at first, but the learning curve is fairly short simply because most have the same components.

Types of SDR applications

SDR applications usually fit one of three categories: proprietary app, free third-party apps, paid third-party apps, and web browser based apps. (Assume each application runs on Windows unless otherwise noted.) Let’s take a look at each.

Proprietary SDR applications

Proprietary apps are those that are designed by the SDR manufacturer and provide native plug-and-play support for the SDR you choose. Proprietary apps give priority support to their own SDR, but some are compatible with other SDRs––or can, at least, read spectrum recordings from other SDRs. Most popular SDRs have a proprietary application. Here are examples of a few proprietary apps:

  • WinRadio App for the WinRadio/Radixon line of SDRs
  • Perseus Software Package for the Microtelecom Perseus
  • SDR# App for the AirSpy line of SDRs
  • SDRuno App for the SDRplay series of SDRs
  • FDM-SW2 App for Elad SDRs
  • SpectraVue App for the RFSpace line of SDRs
  • SmartSDR App for FlexRadio SDR transceivers

Free third party SDR applications

Free third party applications are incredibly popular and some even offer performance and feature advantages over proprietary applications. Third party apps tend not to be associated with any one particular manufacturer––SDR# being a noted exception––and tend to support multiple SDRs. I’m a firm believer in supporting these SDR developers with an appropriate donation if you enjoy using their applications.

  • HDSDR is a very popular application that supports multiple SDRs and spectrum file formats. The layout is simple and operation straightforward.
  • SDR Console is a very powerful and popular application. Like HDSDR, it supports multiple popular SDRs. It is my SDR application of choice for making audio and spectrum recordings.
  • SDR# runs AirSpy SDRs natively, but also supports a number of other receivers including the venerable RTL-SDR dongle.
  • Linrad (Linux)
  • SdrDx (MacOS and Windows)
  • Gqrx SDR (Linux)
  • SDR Touch is a popular SDR application for Android devices (Android)
  • iSDR is one of the only SDR applications currently available for iOS devices. Its functionality is somewhat limited. There are other SDR applications in the works, but at the moment these are in development stages only. (iOS)

Paid third-party apps

Paid third-party apps represent a tiny fraction of the SDR applications available on the market. Indeed, at time of posting, the only one I know about that’s currently on the market is Studio 1, which has been the choice for those looking for an alternative application to the Microtelecom Perseus Software Package.

Web browser-based  SDR applications

The KiwiSDR browser-based application

This is, perhaps, one of the newest forms of SDR applications. While a number of SDR applications (like SDR#, SDR Console and the Perseus Software package) allow for remote control of the SDR via the Internet, there are actually few applications that are purely web browser-based. At the time of this writing, the only one with which I’m familiar is the KiwiSDR application, which allows both the SDR owner and (if set up to do so) anyone else in the world to operate the SDR as if they are at the SDR’s location. In fact, the KiwiSDR only has a web browser-based application, there is no downloadable application. It will allow up to four simultaneous users, and the experience of using a KiwiSDR locally or globally is nearly identical. If you would like to use a KiwiSDR, simply visit http://SDR.hu or https://sdr.hu/map and choose a remote location.

[Note that if you like web-based SDRs, I highly recommend checking out the University Twente WebSDR located in the Netherlands.]

Choosing an SDR

In Parts Two and Three of this primer, we’ll take a closer look at some of the SDRs currently on the market; prices range anywhere from $15 to $6,000. As you can imagine from such a price range, these are not all created equally.

But first, ask yourself what your goal is with your SDR. Do you want to monitor ham radio traffic? How about aviation communications? Follow pirate radio? Listen to a range of broadcasters? Pursue radio astronomy? Is your dream to set up a remote receiver?

Whatever your flavor of radio, you’ll want to keep some of these needs in mind as you explore the SDR options available to you.

Budget

Photo by Kody Gautier

Be honest with yourself: how much are you willing to spend on an SDR? While entry-level SDRs can be found for anywhere from $15-50 US, a big leap in performance happens around the $100 mark. If you’re looking for benchmark performance, you may need to appropriate $500 or more. Whatever you choose, keep in mind that SDRs are only as good as the antennas you hook up to them. Set aside some of your budget to purchase––or build––an antenna.

Compatible applications

As mentioned above, not all SDRs are compatible with anything beyond the OEM/proprietary application. If you have a choice third-party application in mind, make sure the SDR you choose is compatible with it.

Frequency range

If you want an SDR that covers everything from VLF/longwave up to the microwave frequencies, then you’ll need to seek a wideband SDR. Each SDR manufacturer lists the frequency ranges in their specifications sheet. It’s typically one of the top items listed. Modern wideband SDRs can be pretty phenomenal, but if you never plan to listen to anything above 30 or 50 MHz, for example, then I would advise investing in an SDR that puts an emphasis on HF performance. Check both specifications and user reviews that specifically address performance on the frequencies where you plan to spend the bulk of your time.

Recording and processing bandwidth

The new SDRplay RSPduo can display up to 10MHz visible bandwidth (single tuner mode) or 2 slices of 2MHz spectrum (dual tuner mode)

If you plan to make either audio or spectrum recordings, or if you plan to monitor multiple virtual receivers, pay careful attention to an SDR’s maximum recording and processing bandwidth. This bandwidth figure is essentially your active window on the spectrum being monitored. Your active virtual receiver frequencies will have to fall within this window, if you’re making simultaneous recordings. In addition, this figure will determine the maximum bandwidth of spectrum recordings. Some budget SDRs are limited to a small window––say 96 kHz or less––while others, like the Elad FDM-S3, can widen enough to include the entire FM broadcast band, roughly 20 MHz!

Portability

AirSpy’s HF+ was introduced late 2017. Don’t be surprised by its footprint which is similar to a standard business card to its left–this SDR packs serious performance!

If you plan to take your SDR to the field or travel with it, you’ll probably want to choose one that doesn’t require an external power supply. Most late-model SDRs use the USB data cable to power the unit.  This means you won’t need to lug an additional power plug/adapter or battery. Still, many professional grade SDRs require an external power supply.

Recording features

If you plan to make spectrum recordings, determine whether you have many options to set the unit’s processing bandwidth. Some SDR applications have robust recording functionality that allows for both spectrum and audio recordings, including advanced scheduling. Some applications don’t even have audio recording or spectrum recording capabilities. Test drive the application in advance to check out their recording functionality. Of course, if recording is your main interest, you’ll also want to set aside some of your budget for digital storage.

Know your goal!

If your goals are somewhat modest––perhaps your budget is quite low, you simply want to familiarize yourself with SDR operation prior to making a bigger purchase, or you only want to build an ADS-B receiver––then you might be able to get by with a $25 SDR dongle. If you plan to use your SDR as a transceiver panadapter during contesting, then you’ll want to invest in a unit that can handle RF-dense environments.

Identify exactly what you’d like out of your SDR, and do your research in advance. Note, too, that many popular SDR models have excellent online forums where you can pitch specific questions about them.

Scoping out the world of SDRs

Three benchmark receivers in one corner of my radio table: The Airspy HF+ (top), Elad FDM-S2 (middle) and WinRadio Excalibur (bottom).

Now that we have a basic grasp on what SDRs are, what components are needed, and what we should research in advance, we’ll look next at some of the SDR options available to us. In Part Two, we’ll look at budget SDRs; those under $200 US in price. In Part Three, we’ll survey higher-end SDR packages.

Stay tuned for more in Part Two (October–click here to read) and Part Three (November–click here to read)I’ll add links here after publication.

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Presentation at The Circle of HOPE conference next week!

Dear Post Readers,

If you live near or are planning travel to New York City next week, I would encourage you to check out the HOPE (Hackers On Planet Earth) conference at the Hotel Pennsylvania (July 20-22, 2018). The location couldn’t be more accessible: across the street from Penn Station and down the block from the Empire State Building.

The HOPE conference is diverse with an incredibly wide range of topics spanning technology, culture and so more. We’re talking about “hacking” in the best sense: those with the technical knowledge and ingenuity to overcome problems and better understand/explore the world around us. HOPE always has a strong contingent of radio enthusiasts as well–many of whom also attend the Winter SWL Fest in Plymouth Meeting, PA.

This will be my first HOPE conference so I’m especially honored to have been selected as a presenter.

HOPE Presentation

My presentation is titled: Creating a Radio Time Machine: Software-Defined Radios and Time-Shifted Recordings–here’s the description:

Since the earliest days of radio transmitting, individuals and organizations have made an effort to record and preserve radio signals in the form of broadcasts and other over-the-air communications, especially those of historical significance. Now low-cost software-defined radios (SDRs) coupled with today’s faster memory-enhanced computers allow us to record not just individual signals from one radio station at a time, but an entire broadcast band – a wide swath of frequencies – all at once. Each recording from a particular day and time can easily contain dozens, if not hundreds, of stations broadcasting and communicating simultaneously. Later, via a software-defined radio application, recordings can be tuned and listened to (decoded) as if they were live. This talk will discuss how you can build your own “radio time machine” which supports such virtual time shifts by utilizing an inexpensive ($25-$100) SDR, and also show how you can – for free – virtually “travel” through recent history on radio archivists’ preexisting radio time machines.

Time & location: Saturday 1900 Booth

My two main goals with this presentation are to bring more radio converts into our hobby by showing how accessible and dynamic radios are today and also to give The Radio Spectrum Archive some exposure.

HOPE Workshop

I’m also excited to co-host workshop with my good friend, David Cripe (NM0S). Our workshop is titled: Build the HumanaLight: A “Green” Lamp from Trashed Batteries–here’s the description:

This mini-lamp developed for use in impoverished regions where there’s no electrical grid is powered by a surprising, but ubiquitous, waste product – the residual energy in depleted (used) AA batteries. Workshop attendees will build a HumanaLight on a high-quality printed circuit board. The kit includes all necessary parts, even a “dead” AA battery! No experience required. There is a $15 fee for the kit, with the proceeds going to the nonprofit organization Ears To Our World, which developed this valuable and important technology.

Time & location: Friday 1900-2030 Hardware Hacking Village (Mezzanine)

No kit building experience is necessary! We’ll help and guide you as you build an incredibly useful tool!

HOPE Radio

 

In my spare time, I also plan to help with HOPE’s special event amateur radio station W2H. If you can’t attend the event, consider trying to work us on the air! Here are the details:

Amateur Radio Special Event Station W2H and 70cm Repeater

If you’re an amateur “ham” radio operator, you’re part of a hacker community that goes back over a century. Bring your handie-talkie to QSO with the many hams at HOPE to keep up with what’s happening. Visit Special Event Station W2H and operate on several HF/VHF/UHF bands in various voice and data modes to freely communicate with hams around the globe – sans telecom infrastructure! Our 70cm repeater input is 442.875 MHz (PL 167.9) and the output is 447.875 MHz which W2H operators will be monitoring. We also encourage simplex ops on 147.545 MHz and 433.545 MHz (PL 77.0).
More details at http://ham.hope.net.

Time and Location: Friday through Sunday – 18th Floor (next to the 2600 store)

If you can’t tell, it looks like an action-packed weekend! I’m super excited and (admittedly) a little intimidated! Should be lots of fun.

Come join the fun!

Full details can be found at The Circle of HOPE conference website.

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Steve Andrew’s spectrum analyzer software for SDRplay SDRs now available for download

A few weeks ago, we posted an announcement that spectrum analyzer software was being developed for the SDRplay RSP software defined radio series. Many thanks to Andy, at SDRplay, who shares the following announcement:

We are pleased to announce the availability of the first cut of Spectrum Analyser software developed by Steve Andrew specifically for the RSP line of products. Please note that this is first alpha software and so it is still very much in development and some features are still to be added. Currently supported are:

  • RSP1
  • RSP2/RSP2pro
  • RSP1A

This first alpha release gives a good idea as to the look and feel for the software. The main functional limitation is that sweeps of greater than 10 MHz are not currently supported. Steve is currently re-working the algorithms for providing wider sweeps than 10 MHz to improve sweep time and remove the issue of the DC spike in ZIF mode, so please bear with him.

We recommend using the software with AGC turned off and use manual control of the gain for better display stability.

Please see the Spectrum Analyser webpage: https://www.sdrplay.com/spectrum-analyser

Best regards,

SDRplay Support

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A review of the SDRplay RSPduo 14-bit dual tuner SDR

The new SDRplay RSPduo

Moments ago, I posted a press release from the UK-based software-defined radio manufacturer, SDRplay, announcing their latest product: the RSPduo: a 14-bit Dual Tuner SDR.

I should start with the disclaimer that, not only was I sent an RSPduo to review and evaluate, but SDRplay has been a supporter of the SWLing Post for a few years now.  You’ve no doubt seen their ads in the upper right corner of our site. After I reviewed their first SDR (the RSP1) I discovered that SDRplay––all of their staff and supporters––welcome constructive criticism and even invite frank discussions. They’re a company with integrity.  No doubt, this is why I agreed to alpha- and beta-test their SDRs. Fortunately, I’ve not been disappointed.

As a company, moreover, SDRplay breaks the mold––and in very good ways:

  • SDRplay is a small company that employs actual radio enthusiasts. Their designs and software cater to DXers, SWLs, hams, scanner enthusiasts, amateur astronomers, experimenters, and makers, among others.
  • SDRplay designs and builds their products in the United Kingdom. No doubt they could increase their profit margin by using manufacturing centers in China, but they choose not to do so, to the benefit of their products.
  • The quality of the company’s products is, at least to date, excellent.
  • SDRplay’s product pricing is nonetheless quite affordable

That last item, in particular, is a head-scratcher.  Considering these facts, how does SDRplay still manage to keep their pricing so competitive? I only wish I knew.  When the company released the RSP1A last year, I had already spent a few months with alpha and beta units, mulling over their respective merits (and there were many).  So I was simply gobsmacked when they announced that the price would be just $99 US. I rather figured the company was leaving money on the table, although I was pleased to announce this price to my readers here.

Fast-forward to two weeks ago: I received the new RSPduo to review. And the price this time? $279 US. While this is currently the priciest product in the SDRplay line, let’s go over what makes this SDR special…and why I still think SDRplay may be leaving money on the table.

Introducing the SDRplay RSPduo

 

The RSPduo is unlike any other SDR in the SDRplay product line, and, indeed, unlike most of the budget SDRs currently on the market.

As “duo” implies, this RSP features dual independent tuners, both piped through a single high-speed USB 2.0 interface. With the RSPduo, you can explore two completely separate 2 MHz bands of spectrum anywhere between 1kHz and 2GHz.

SDRplay lays out several use-scenarios in their press release:

  • The ability to simultaneously receive on two totally independent 2 MHz spectrum windows anywhere between 1 kHz and 2 GHz
  • Simultaneous processing from 2 antennas enables direction-finding, diversity, and noise-reduction applications
  • Ideal for cross band full-duplex reception, e.g. HF + VHF, or VHF + UHF
  • Simultaneous Dump1090 and VHF ATC reception
  • Simultaneous monitoring and recording of 2 ISM bands
  • Use SDRuno to seamlessly control and manage the dual tuner in a single environment.

Externally, the RSPduo bears a strong resemblance to the RSP2pro. Internally, however, it’s quite different.

Besides featuring a second independently controlled tuner, the RSPduo also sports 14 bit ADCs and a completely re-designed RF front end, which enhances receiver selectivity and improves dynamic range.

In short, the RSPduo is like having two SDRs in one.

Performance

I received the RSPduo during a very busy time of the year: the build up to the Hamvention in Xenia, OH.

One of the first things I noticed about the RSPduo is its weight. When I picked up the package from SDRplay, I could tell it weighed at least twice that of the RSP1A. One reason for the extra heft is that the RSPduo, like the RSP2 Pro, has a metal enclosure. I’m willing to bet the RSPduo also has more shielding––adding even a little extra weight.

I’ve had the RSPduo on the air for more than a week now, and have checked out all of its major functions and begun to learn the nuances of navigating the dual receivers in the latest version of SDRuno.

SDRplay will, I feel sure, post a primer video on using the various dual tuner functions in the coming weeks.

 

Installation of the software, even in pre-production, was totally a “plug-and-play” experience. Simply install the SDRuno software package with the RSPduo disconnected from the USB port.  Plug in the RSPduo, and wait for the USB driver to load, then open SDRuno. That’s it. You’re on the air!

 

As I’ve indicated, the RSPduo is really like having two RSP1As in a single RSP2 Pro package. One of these dual receivers––the master––can utilize either a standard 50 ohm SMA antenna port, or a Hi-Z port. The second receiver uses one 50 ohm SMA antenna port just like the RSP1A.

I much prefer using the Hi-Z port for everything longwave and mediumwave.  I did hook up both antenna ports on the master receiver, however, and switched back and forth between the two. At least in my antenna setup, I feel like the Hi-Z option lends itself to improved sensitivity on these bands. It’s not a dramatic difference––indeed, looking at the spectrum display one barely notices the difference––but my ears told me the noise floor was lower and signal strength slightly better with the Hi-Z port. Above 2 MHz, the Hi-Z port is not prefered since it lacks the same level of RF pre-selection as the 50 ohm ports provide.

Unlike the Hi-Z port with the RSP2, the RSPduo treats the Hi-Z port more like an auxiliary antenna port. When I employed the Hi-Z port in the HF bands, I did notice small spurious noises, but this might have been due to my antenna port configuration here in the shack (my Hi-Z connector is simply attached to the shield and center conductor of my coax).

Again, however, for anything above 2 MHz, SDRplay suggests using the 50 ohm ports.

How to set up dual receivers on one screen/monitor

Listening to the FM broadcast band on the main receiver and Voice of Greece shortwave on the second receiver.

One of the first things I was eager to do was to run the dual receiver functionality on one monitor.  Although SDRplay makes this a pretty simple process in the latest version of SDRuno, I still stumbled a bit as I learned to navigate the controls.

Here’s a quick primer to get both receivers on the air on one monitor/screen:

  • First, open SDRuno in “single receiver mode” (the typical SDRuno default).

  • Next, click on the “RSPduo mode” button and select one of the modes.  In this case, I’m not running the ADS-B application, so I’ll choose “DUAL (NORMAL)”.

  • Now, to format the “Master” receiver windows so they only use the top half of the monitor, click on the OPT button.

  • Select “Auto Layouts” and “RSPduo Master.”

If you’ve followed these steps with me, your screen should look something like this:

Now you’ll want to start the second receiver. Do this by opening the SDRuno application again (as if you were opening SDRuno for the first time). Make sure you’ve selected your RSPduo if you have more than one RSP connected.

The new instance of SDRuno will fill the entire screen by default, so you’ll need to format it to occupy the lower half of the screen.

Simply click on the OPT button again, select “Auto Layouts,” and “RSPduo Slave.”

Your full screen should now look something like this:

Now you can start using both receivers, but you’ll have to always start the “Master” receiver first. In fact, the “Master” receiver must always be active in order to operate the “Slave” receiver. You can always close the “Slave” receiver without affecting the “Master” receiver; however, if you close the “Master” receiver, you will effectively close both receivers.

Again, I fully expect SDRplay will soon produce a demonstration video showing how you can navigate SDRuno’s new dual-receiver functionality.

Comparisons

As I’ve mentioned in most previous SDR reviews, I do like to take a considerable amount of time to set up SDR comparisons.

Herein lies the difficulty of reviewing an SDR’s performance. Because the user has so much power to control variables and thus shape the receiver’s function, it’s actually quite hard to make an “apples-to-apples” comparison––insuring that all important filters, gain controls, DSP, etc., are as close to identical as possible.

One tool that helps me do this is SDR Console, since it can control a number of SDRs and receiver parameters can be set up identically.  Unfortunately, the RSPduo is so new, SDR Console doesn’t yet support it.

I did use SDRuno to compare the RSPduo with the RSP1A. Fortunately, I could actually run two separate instances of SDRuno simultaneously (and on different monitors, in my case). Both were hooked up to the same antenna via my ELAD ASA15 antenna splitter amplifier.

The RSPduo’s improved dynamic range gives it an advantage in terms of noise floor, sensitivity, and selectivity.

The improved performance is not dramatic––but I understand it might be especially detectable to those who want a receiver with a more robust front end.

In fact, the RSPduo’s 50 ohm coaxial ports have quite an array of automatically configured front end filters:

Low Pass

  • 2 MHz Band Pass
  • 2-12 MHz
  • 12-30 MHz
  • 30-60 MHz
  • 60-120 MHz
  • 120-250 MHz
  • 250-300 MHz
  • 300-380 MHz
  • 380-420 MHz
  • 420-1000 MHz

High Pass

  • 1000 MHz

And an array of notch filters

FM Notch Filter:

  • >30dB 77 – 115MHz
  • >50dB 85 – 107MHz
  • >3dB 144 – 148MHz

MW Notch Filter:

  • >15dB 400 – 1650kHz
  • >30dB 500 – 1530kHz
  • >40dB 540 – 1490kHz

DAB Notch Filter:

  • >20dB 155 – 235MHz
  • >30dB 160 – 230MHz

The thing is, I live in an RF quiet area, so I can’t fully take advantage of the SDRuno’s more robust front end.

In head-to-head comparisons with the RSP1A, the RSPduo’s performance edge is discernible. Again, I suspect it would be a bit more obvious if I lived in an urban setting with blowtorch stations in the neighborhood. Using the Hi-Z antenna port in the mediumwave portions of the band, the RSPduo has a performance edge over the RSP1A, as well.

Should you grab the RSPduo?

The new SDRplay RSPduo

Anytime a new product hits the market, I ask myself if this is the sort of product that would tempt me to reach for my hard-earned cash.

The short answer?  Absolutely! Take my money, please!  There is no other sub-$300 SDR on the market currently that has the dual tuner functionality of the RSPduo. Thing is, I’ve only had the RSPdup a couple of weeks–there’s so much yet I want to explore here–especially diversity reception!

But what if you already have an SDRplay SDR? Afterall, the RSP1A was only released a few months ago, and the RSP2 series only a year before that.

Here’s my opinion:  If you’re an RSP1A or RSP2 owner who is pleased with this SDR’s performance, I wouldn’t necessarily urge you to purchase the RSPduo simply for the modestly enhanced performance characteristics. SDRplay hasn’t retired the RSP2 and RSP1A designs because each model still holds its own, has a purpose, and obviously enjoys a healthy market.

The RSP1A is the affordable yet high performance entry model in the SDRplay product line. It’s really the best value in the radio world, in my humble opinion, at just $99 US.  Som enjoy.

The RSP2 and RSP2pro provide excellent performance, three software-selectable antenna inputs, and clocking features, all of which lend it to amateur radio, industrial, scientific, and educational applications; it is a sweet SDR for $169 or $199 (Pro version). I know of no other SDRs with this set of features at this price point. If I liked the characteristics of the RSPduo, but didn’t really need a dual receiver for my application, I’d probably reach for the RSP2 Pro.

But if you have the original RSP, and like SDRuno and the SDRplay community, then I would certainly consider this an opportunity to upgrade. For $279, you’re getting a dual receiver SDR with excellent performance characteristics that will easily surpass the original RSP––considering that you’re essentially getting two very good SDRs in one.

And if you’re all over the spectrum (aren’t we all a bit––quite literally?) in terms of usage, the RSPduo is a fascinating machine for running, say, an ADS-B receiver while independently using the same SDR box to monitor other parts of the spectrum. Or one can listen for FM DX on one receiver while trying to snag elusive LW DX on the other.

Better yet, the RSPduo only uses one USB port––an important factor if you’re using a laptop or tablet. Of course, having two receivers on two different antennas, while sharing one data port, means syncing them for diversity reception is especially effective. This alone will sway many SDR experimenters in favor of this rig.

I have yet to compare the RSPduo with the brilliant little AirSpy HF+. The AirSpy HF+ is not a wideband receiver like the SDRplay RSP series; it only covers 9 kHz to 31 MHz and 60 to 260 MHz. But if your primary concern is HF performance, the HF+ and its excellent dynamic range will impress you, if you’re anything like me. It’s also a bargain at $199––very hard to beat!

The RSPduo is a good value, in my opinion––and an inexpensive upgrade to a proper dual receiver SDR––so if that’s the sort of thing you’d like to add to your shack, go ahead and bite the bullet!

In fact, I suspect SDRplay will quickly sell out of all of the units they bring to the 2018 Hamvention (SDRplay: pack some extras!). I’m happy to see the company continue to push the price and performance envelope to such exceptional ends. I’m also looking forward to the many applications SDRplay customers (and our readers) find for the RSPduo.

Stay tuned! I plan to post more comparisons in the future.

And if you acquire an RSPduo and find some new and fun applications for it, please share!

Click here to check out the RSPduo at SDRplay.com.

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SDRplay announces the RSPduo: A 14-bit Dual Tuner SDR

(Source: SDRplay Press Release)

SDRplay announces the RSPduo – A 14-bit Dual Tuner SDR

Today at the Dayton Hamvention, SDRplay Limited is announcing the launch of a new Software Defined Radio product – the RSPduo.

The RSPduo is a radical new addition to the RSP line of SDR receivers from SDRplay. Architecturally, it is different from any previous RSP in that it features dual independent tuners, both piped through a single high-speed USB 2.0 interface.

The SDRplay RSPduo is a dual-tuner wideband full featured 14-bit SDR which covers the entire RF spectrum from 1kHz to 2GHz giving 10MHz of spectrum visibility. Initially using Windows based ‘SDRuno’ supplied by SDRplay, you can simultaneously monitor two completely separate 2MHz bands of spectrum anywhere between 1kHz and 2GHz.

Superficially the RSPduo looks identical to the highly popular RSP2pro and will be able to operate in a very similar way.

However, it also allows a completely new and exciting set of usage scenarios such as:

  1. Simultaneous monitoring of two widely spaced bands – e.g. 40m (HF) and 2m (VHF)
  2. Mixing and matching applications simultaneously – e.g. ADS-B and ATC scanning
  3. Phase and time coherent demodulation of two receivers

Scenario 3 is very difficult to achieve with two separate USB devices because of the uncertainty of USB latency. The RSPduo overcomes this limitation because all traffic goes through a single USB interface, thus enabling the possibility of the development of various types of diversity demodulation such as: spatial, frequency and polarisation which can bring
huge benefits in terms of improved performance.

Jon Hudson, Marketing Director at SDRplay commented:
“As well as adding a second independently controlled tuner, which in itself, offers a whole new set of exciting usage possibilities, the SDRduo features 14bit ADCs and a completely re-designed RF front end. These changes provide better RF selectivity and even more dynamic range, offering outstanding performance under extremely challenging reception conditions. The combination of performance and features makes the RSPduo our highest spec RSP yet and sets a new benchmark in the sub $300 SDR market”

Due to its exceptional combination of performance and price, the RSP family of receivers have become very popular and the RSPduo provides the next level of functionality for both amateur radio enthusiasts as well as the scientific, educational and industrial SDR community.

As well as being demonstrated at Hamvention, the RSPduo is available direct from SDRplay or via SDRplay’s network of channel partners and resellers

The RSPduo is expected to retail at approximately $279 USD (excluding taxes) or £199 GBP (excluding taxes).

For more information visit the SDRplay website on www.sdrplay.com

About SDRplay: SDRplay limited is a UK company and consists of a small group of engineers with strong connections to the UK Wireless semiconductor industry. SDRplay announced its first product, the RSP1 in August 2014

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