{"id":33915,"date":"2018-09-02T07:23:44","date_gmt":"2018-09-02T11:23:44","guid":{"rendered":"https:\/\/swling.com\/blog\/?p=33915"},"modified":"2018-11-04T09:50:51","modified_gmt":"2018-11-04T13:50:51","slug":"software-defined-radio-primer-part-1-introduction-to-sdrs-and-sdr-applications","status":"publish","type":"post","link":"https:\/\/swling.com\/blog\/2018\/09\/software-defined-radio-primer-part-1-introduction-to-sdrs-and-sdr-applications\/","title":{"rendered":"Software Defined Radio Primer Part 1: Introduction to SDRs and SDR applications"},"content":{"rendered":"
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The new ELAD FDM-S3.<\/p><\/div>\n

The following article originally appeared\u00a0in the June 2018 issue of The Spectrum Monitor magazine<\/a>:<\/em><\/strong><\/p>\n

\n

SDR Primer Part 1: Introduction to SDRs and SDR applications<\/h1>\n

I author a radio blog known as the SWLing Post<\/a>;<\/i> as a result, I receive radio-related queries from my readers on a daily basis. \u00a0Among the most common questions are these:<\/p>\n

\u201cSo, what is an SDR, exactly? Are these better than regular radios?\u201d<\/p><\/blockquote>\n

and\/or,<\/p>\n

\u201cI think I\u2019d like to buy an SDR. Which one do you recommend?\u201d<\/p><\/blockquote>\n

Great questions, both! But, before I address them, I must let the reader know that they are also \u201cloaded\u201d questions: simple enough to ask, but quite nuanced when it comes to the answers.<\/p>\n

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\u2019ll look at affordable SDRs: those costing less than $200 US. In part three, we\u2019ll take a look at pricier models and even include a few transceivers that are based on embedded SDRs.<\/p>\n

But before we begin, let\u2019s start with the most basic question: What <\/b>is<\/i><\/b> a Software Defined Radio (SDR), exactly?<\/b><\/p>\n

Not your grandpa\u2019s radio<\/h2>\n

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Here\u2019s how Wikipedia defines SDR:<\/p>\n

\u201cSoftware-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.\u201d<\/p><\/blockquote>\n

Whereas your grandpa\u2019s radio was all hardware<\/i>\u2013\u2013in the form of filters, mixers, amplifiers, and the like\u2013\u2013SDRs are a mix of hardware and<\/i> software<\/i>. With the exception of tabletop transceivers and receivers with embedded software and systems (which we\u2019ll discuss in part three of our investigation), SDRs typically take on a \u201cblack box\u201d 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\u2019s 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, \u201cblack box\u201d SDRs often look like a nondescript piece of portable computer hardware\u2013\u2013something like an external portable hard drive.<\/p>\n

Why would you want an SDR?<\/h2>\n

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? \u00a0Below, I\u2019ll list some of the most appealing reasons:<\/p>\n

Bang-for-buck<\/h3>\n
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The Airspy HF+ (top) and FDM-S2 (bottom). Photo by Guy Atkins.<\/p><\/div>\n

By and large, SDRs are quite a value when compared to legacy all-hardware radios. For example, I wouldn\u2019t hesitate to pit my SDRs\u2013\u2013such as the $500 Elad FDM-S2<\/a> or $900 WinRadio Excalibur<\/a>\u2013\u2013against legacy receivers that cost two to three times their price. Indeed, my $200 AirSpy HF+<\/a> SDR will give many DX-grade ham radio general coverage receivers a real run for their money. They\u2019re that good.<\/i><\/p>\n

Spectrum display<\/h3>\n

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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. <\/i>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\u2013\u2013a visual representation\u2013\u2013of what\u2019s on the radio. Using legacy receivers now often makes me feel like I\u2019m cruising the bands with blinders on. After becoming accustomed to having a spectrum display, there\u2019s simply no way I\u2019d want to be without at least one SDR in my shack.<\/p>\n

Powerful tools<\/h3>\n
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I like how clean the user interface is for this SDR application (SDRuno) window that controls the SDR’s frequency, mode, filters and notch.<\/p><\/div>\n

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\u2019s performance and listening experience is simply unsurpassed. In fact, it\u2019s almost a curse for SDR reviewers like me\u2013\u2013comparing 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.<\/p>\n

Multiple virtual receivers<\/h3>\n
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SDR Console makes managing multiple virtual receivers a breeze.<\/p><\/div>\n

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\u2013\u2013in 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.<\/p>\n

Recording tools<\/h3>\n

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.<\/p>\n

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SDR Console recording dialog box<\/p><\/div>\n

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.<\/p>\n

So imagine that propagation is stellar one evening, or there\u2019s a global pirate radio event just when you\u2019re going to be away from home: simply trigger a spectrum recording and do a little radio time travel tuning later. It\u2019s that easy.<\/p>\n

Constant upgrades<\/h3>\n

Both SDR applications and SDR firmware are upgradable from most manufacturers. In fact, I\u2019ve found that the most affordable SDRs tend to have the most frequent upgrades and updates. Updates can have a positive impact on an SDR\u2019s 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\u2019s what\u2019s so brilliant. As a user you can make requests; your SDR\u2019s developers might, if they like the idea, be able to implement it.<\/p>\n

So, what\u2019s not<\/i> to love?<\/h2>\n

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\u2019t. For some radio enthusiasts, SDRs do have some unfortunate disadvantages:<\/p>\n

First, if you\u2019re primarily a Mac OS or Linux user, and\/or prefer one of these platforms, you\u2019ll 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\u2013\u2013and neither was particularly good. I considered purchasing a copy of Windows for my MacBook, but decided to invest in a tower PC, instead.<\/p>\n

Second, one of the great things about legacy radios is that with just a radio, a power source, and an antenna, you\u2019re 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\u2019ve spent several summers in an off-grid cabin in Prince Edward Island, Canada. My spot is superb for catching DX, and there\u2019s 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.<\/p>\n

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The ELAD FDM-DUOr (receiver).<\/p><\/div>\n

With this said, keep in mind that there are fully functional tabletop radios (like the Elad FDM-DUO<\/a>\u00a0and FDM-DUOr) that are actually SDRs, providing an easy way to bypass this concern.<\/p>\n

Finally, there are simply some people who do not care to mix PCs and radio. I\u2019ve a friend who\u2019s 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\u2013\u2013as a former programmer, I used to feel that way myself. \u00a0But the world of SDRs lured me in…and now I\u2019m a convert.<\/p>\n

Scope of this primer series<\/h2>\n

The world of SDRs is the fastest growing, most dynamic aspect of the radio world. Because of this, I simply can\u2019t include all <\/i>SDRs currently on the market in this primer. \u00a0Let\u2019s face it: there are just too many, and it is beyond the scope of this article to try to cover them all. Instead, I\u2019ve curated my list, by no means comprehensive, to include a selection of the most popular and widely-used models.<\/p>\n

I\u2019ll be focusing on SDR receivers<\/i> unless otherwise noted. In Part Three, I\u2019ll call out some popular SDR transceivers. Additionally, I\u2019ll bring my attention to bear on the \u201cblack box\u201d variety of SDRs.<\/p>\n

This primer is long overdue on my part, so I\u2019ll 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.<\/p>\n

Thus far we\u2019ve defined an SDR and discussed its advantages and disadvantages.<\/p>\n

Now, let\u2019s take a closer look at what you\u2019ll need to build a station around an SDR.<\/p>\n

Assembling an SDR station<\/h2>\n
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Guy Atkins’ laptop running HDSDR software in his SUV; the receiver is an Elad FDM-S2. (Photo: Guy Atkins)<\/p><\/div>\n

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\u2019s discuss this component by component.<\/p>\n

A computer<\/h3>\n

By virtue of reading this primer now being displayed on your screen, unless you\u2019ve printed it out, I\u2019m guessing you have access to a computer of some sort.<\/p>\n

SDRs are really quite flexible in terms of computer requirements. SDRs are compatible with:<\/p>\n