Alexa skills come in all shapes and sizes, from the trivial random fact skill, to a fully fledged news reader.
Some have little or no input, while others try to carry out a conversation with you.
Recognising that Alexa might be new to some people, and that the Shortwave Signals skill tries to capture everything from you in a single phrase, I wanted to give readers a guide on how to get the best from the skill, as well a little background on how Alexa ‘understands’ or ‘misunderstands’ what you said.
You have two ways of starting an Alexa Skill:
Open the skill using its name
Ask the skill using its name
Opening the skill is a great place to start when you’ve first installed a skill. It should provide you with an introduction, then offer to answer a question or suggest how you can get further help.
Once you are familiar with a skill, you can save time by ‘Asking’. This cuts through the opening pleasantries and gets on with the job.
A skill doesn’t get approved by Amazon unless it supports these approaches in an appropriate way.
With that out of the way, the essential thing is to make sure that your words are clear and don’t blur together. I remember eating lunch at my desk while developing the skill, and then wondering why Alexa was making such a mess of my questions.
How Do Alexa Skills Recognise What You Say?
The short version is that skill developers have to provide training phrases to Alexa with two objectives in mind; to figure out what you want to do, and to recognise the parts of those phrases that contain important information.
If you were writing a weather skill, those phrases might look like this:
What is the weather like in [placename]
Will it rain in [placename] on [date]
What will the weather be like on [date] in [placename]
The challenge is to figure out the different ways that people might ask a question, and then help Alexa know what parts of the question are important to the skill. This data can can include numbers, dates, times, real world locations, famous places, famous people, countries, languages, and much more.
So let’s see how that works in the Shortwave Signals skill.
The Simplest Possible Question
The simplest question you can ask is to identify a signal by frequency – you’ve stumbled across something of interest and you’re not sure what it is.
A question directed to your Alexa device would sound like this:
Ask Shortwave Signals
Who broadcasts on one five five eight zero kiloHertz
I usually leave a slight pause after each line, and make sure that words don’t run into each other. Always say the frequency as digits, as this is much more reliable than trying to express it in thousands, hundreds, tens and so forth.
It’s good practice to put kiloHertz on the end as this aids Alexa in interpreting the frequency part of your question.
A common gotcha is not leaving enough of a gap between the frequency and the word kiloHertz. If the words blur together, Alexa sees a mixture of words and numbers where the frequency ought to be and doesn’t pass it through to the skill.
Adding a Broadcast Time to your question
Depending on the frequency you pick, you might get quite a few results.
This is particularly common when the frequency belongs to one of the main international broadcasters, or a commercial shortwave station like WRMI.
At present, I’ve set a limit of 15 results so you’re not stuck listening to a long list of broadcast information, although if all else fails, you can say:
To make it clear you want to specify a broadcast at a particular time, add this to your question:
Note that times are always in UTC, and using AM and PM is a reliable way of qualifying your time.
Now your question sounds like this:
Ask Shortwave Signals
Who broadcasts on one five five eight zero kiloHertz
Make sure you put the word ‘at’ in front of the time, as it makes it clear that this is the time ‘at’ which the broadcast is active. It also neatly separates the frequency part of the question from the time part.
Searching across a time range
If you are sitting on a frequency and wondering what might be coming up next, you can add a time range to your question.
A time range is instead of using a broadcast time.
You would add this to your question:
from 3PM to 4PM
Notice how the range is described FROM 3PM TO 4PM
Now your question sounds like this:
Ask Shortwave Signals
Who broadcasts on one five five eight zero kiloHertz
from 3PM to 4PM
Using FROM and TO makes it easier for Alexa to detect the time range in your question.
Adding a Language to your question
Adding a commonly recognised language to your question is easy.
To specify a language in your question you would add:
Putting the word ‘in’ makes it clear that the word that follows is a language, and it also makes sure that the word kilohertz is separated from the language word. If you let the words run together, Alexa might think the language is ‘kiloHertz English’.
Now your question looks like this:
Ask Shortwave Signals
Who broadcasts on one five five eight zero kiloHertz
The Most Complex Questions
The most complex questions you can ask combine a frequency with a language and broadcast times. For example:
Ask Shortwave Signals
Who broadcasts on one five five eight zero kiloHertz
From 3PM to 8PM
Ask Shortwave Signals
Who broadcasts on one five five eight zero kiloHertz
Some Languages are tough to search
Commonly recognised languages are easy for Alexa to detect. These include English, French, German, Russian and many more.
Things get tricky when using more obscure languages.
A good example that I’ve struggled with is Oromo. No matter how carefully and comically I try and pronounce the word Oromo, Alexa always hears something similar to but not quite the same as Oromo, the most frequent misspelling being Orono. This phonetic re-interpretation of less common languages is a tough problem, even though my training data tells Alexa that this part of the question is a language.
Perhaps this will improve over time as Amazon tweak their service.
It’s all about clarity and how you phrase your question. I’ve mumbled my way through Alexa’s built-in skills as well as third party ones, and it’s amazing how well it copes.If you’ve tried a skill and it’s stumbled, double check the sample phrases that come with the skill and give it another try.
Amazon use those phrases to test the skill before it is approved, so you know that they are a good place to start forming your own questions.
Thank you, Mark! Almost every Alexa skill is subject to the same issues you mention above. I find that I need to “think like Alexa” in order to ask skill questions properly. I’ve actually found your skill to be one of the easiest I’ve used. The tutorial above really helps form questions properly.
Last month we covered Part One of our three-part primer on software-defined radios (SDRs). While last month’s Part One focused on the nomenclature and components of a functioning SDR system, Part Two will take a look at some affordable SDR station options that will propel you into the world of SDRs for less than $200 US. We’ll cover Part Three in November, and we’ll dive a little deeper into the rabbit hole and cover higher-end SDRs and ham radio transceivers with embedded SDRs.
SDRs are affordable
If there’s one thing I’d like you to take away from this part of our primer, it’s that SDRs are truly affordable. For less than the price of a typical full-featured shortwave portable, you can own an SDR that covers almost all of the listening spectrum, and that does so with excellent performance characteristics.
We’re lucky to live in a time of phenomenal radio innovation. When I first jumped into the world of SDRs, the least expensive SDR that covered any of the bands below 20 MHz was about $500. That was only a few years ago, in 2010 or so.
Yet in the past three years, affordable SDRs have become the dominant radio product on the market. And these modestly-priced products have made the barrier of entry into the SDR world crumble overnight.
Today, even a $100 SDR has more features, more frequency range, and more functionality than a $1000 SDR from just a decade ago. Times have changed dramatically; indeed, the pace of innovation in this craft is simply amazing.
Before we begin looking at some choice sub-$200 SDRs, I’d just like to direct your attention to the first part of our SDR Primer (click here to read). Specifically, I’d like you to note one element I discussed in that article: the vital importance identifying your goals as an SDR owner. In other words, how do you plan to use your SDR? If you’re only seeking an SDR to listen to local ham radio repeaters, track cubesat satellites, or gather ADS-B information from aircraft, a $25 SDR will more than suffice. If you wish to use the SDR as a transceiver panadapter, or you wish to chase weak signal DX on the HF bands, then I’d suggest you invest a bit more.
I’d also like to remind you, as I noted in the previous article, that this primer will be limited in the SDRs I highlight. The reason for this is simple: there now exists a vast ocean of SDRs on the market (just search eBay for “SDR” and you’ll quickly see what I mean) so all models simply can’t be included in this introductory foray. I’ll be focusing here on several SDRs that cover the HF spectrum and above. I’ll also focus on SDRs with which I have personal experience, and which I consider to be “enthusiast” grade among a healthy community of users. Of course, this part of the primer will only include HF-capable receivers that cost a total of $200 or less.
Let’s take a look at what’s on the market in order of price, starting with the most affordable.
$10-$25: The RTL-SDR dongle
No doubt, many of you reading this primer have purchased an RTL-SDR dongle. Over the years, I’ve owned three or four of them and have even purchased them for friends. These dongles originally appeared on the market many years ago as mass-produced DVB-T TV tuner dongles based on the RTL2832U chipset. Very soon, users discovered that with just a little hacking, the dongle was capable of much, much more than its original intended purpose.
The dongle resembles a USB memory stick. On one end, you’ll find a standard USB connector. On the other, you’ll find an antenna port, typically SMA, to which one connects an antenna. Although it goes without saying, here’s a friendly reminder: make sure you’re choosing an antenna to match the frequency range you’re exploring!
I’ve seen this older model of RTL-SDR being sold for $9 at Hamvention.
Early RTL-SDR dongles couldn’t cover the HF bands or lower, but many models can now cover a gapless 500 kHz all the way to 1.75 GHz.
So, what can you do with an RTL-SDR dongle? In short, quite a lot! Here are a few of this simple device’s many applications and uses in our hobby. It can:
become a police radio scanner
monitor aircraft and ATC communications
track aircraft with ADS-B decoding and read ACARS short messages
scan trunking radio conversations.
decode unencrypted digital voice transmissions such as P25/DMR/D-STAR.
track maritime boat positions like a radar with AIS decoding.
And, of course, you can listen to any signals between 500 kHz up to 1.75 GHz––essentially, most of the radio listening landscape.
Is $25 still a little high for your budget? RTL-SDR dongles can be found for as low as $10 US, shipped, on eBay. While the cheapest of these dongles may suffice for some radio applications, I’m partial to the dongle produced by RTL-SDR.com, since they’re built in a tough metal enclosure, have thermal pad cooling, as well as extra ESD protection. Amazon has an RTL-SDR.com dongle starter package with antenna options for about $26. That’s, what, the price of three hamburgers? Two orders of fish and chips? And worth it.
Many third-party SDR applications support the RTL-SDR dongle, but my favorite is SDR# (click here to download).
So, the major pros of this little SDR are 1) obviously, the price; 2) many, many uses; and 3) the fact that it’s the most popular SDR on the market, with a massive online user base.
What about negatives? Well, to be frank––aside from the dongle’s budget-busting versatility––the fact is that “you pay for what you get.” You’re investing just $10-$27 in this receiver, so don’t expect exceptional performance especially on anything lower than 50 MHz. On HF, for example, the RTL-SDR could easily overload unless you employ external filtering.
Indeed, I’ve never used the RTL-SDR for HF DXing, but I currently have three dongles in service 24/7: two as ADS-B receivers, and one as a receiver for the LiveATC network. And these work hard. Indeed, It’s a workhorse of a device!
I suggest you grab an RTL-SDR and use it as an accessible step into the world of SDRs, and as an affordable single-purpose tool to unlock the RF spectrum!
When you invest a modest $99 US (or $120 shipped), and purchase the RSP1A, you take a major step forward in the SDR world.
UK-based SDRplay is an SDR designer and manufacturer that focuses on enthusiast-grade, budget wideband SDRs. SDRplay designs and manufactures all of their SDRs in the United Kingdom, and over the past few years, they’ve developed a robust user community, extensive documentation, and, in my humble opinion, some of the best tutorial videos on the market.
SDRuno windows can be arranged a number of ways on your monitor.
Although the RSP series SDRs are supported by most third-party SDR applications, SDRplay has their own app: SDRuno. Moreover, SDRuno is a full-featured, customizable application that takes advantages of all of this SDR’s performance potential and features. I should mention that installing the RSP1A and SDRuno is a pure plug-and-play experience: just download and install the application, plug in the RSP1A to your computer, wait for the USB driver to automatically install, then start SDRuno. Simplicity itself.
While the RSP1A is SDRplay’s entry-level wideband SDR, it nonetheless plays like a pro receiver and truly pushes the envelope of performance-for-price, and for other SDR manufacturers, sets the bar quite high. The RSP1A is a wideband receiver that covers from 1 kHz all the way to 2 GHz; equally pleasing the longwave DXer, HF hound, tropo-scatter hunter, and even radio astronomer. This affordable SDR really covers the spectrum, quite literally. Not only does the RSP1A cover a vast frequency range, but its working bandwidth can be an impressive 10 MHz wide and via SDRuno, the RSP1A will support up to 16 individual receivers in any 10 MHz slice of spectrum. All this for $99? Seriously? I assure you, yes.
Think of the RSP1A as the sporty-but-affordable compact car of the SDR world. It delivers performance well above its comparatively modest price, and is fun to operate. In terms of DX, it gets you from point A to point B very comfortably, and is a capable receiver which will help you work even weak signals––and very reasonably!
If you’re looking to explore the world of SDRs, would like a capable receiver with great LW/MW/HF reception to do it with, but also want to keep your budget in check, you simply can’t go wrong with the RSP1A.
Many years ago when I ventured into the world of SDRs, one of the only affordable SDRs which covered the HF bands was the FUNcube Dongle Pro+.
The Funcube Dongle Pro+, which resembles the RTL-SDR “stick” type dongle, was originally designed as a ground receiver for the FUNcube Satellite (cubesat) project initially made possible by AMSAT-UK and the Radio Communications Foundation (RCF). The original Funcube dongle did not cover any frequencies below 64 MHz, but the Funcube Dongle Pro+ added coverage from 150 kHz to 1.9 GHz with a gap between 240 MHz and 420 MHz.
In full disclosure, I’ve never owned a FUNcube Dongle Pro+, but I have used them on several occasions. I believe you would find that it is prone to overloading if you use a longwire antenna that’s not isolated from the dongle. In other words, during such use it seems to be subject to internally-generated noise. In my experience, the Pro+ worked best when hooked up to an external antenna fed by a proper coaxial cable.
To be clear, with the advent of SDRplay and AirSpy SDRs, the FUNcube Dongle Pro+ is no longer the budget SDR I would most readily recommend.
Still, the Pro+ is a very compact dongle that has a great history, and around 2012 really pushed the performance-for-price envelope. It still has many dedicated fans. No doubt, this product has had a huge influence on all of the sub $200 SDRs currently on the market, thus we owe it a debt of gratitude.
In 2016, after the remarkable success of the original RSP, SDRplay introduced the RSP2 and RSP2 Pro SDRs. The RSP2 is housed in an RF-shielded robust plastic case and the RSP2 Pro is enclosed in a rugged black painted steel case. In terms of receivers and features, the RSP2 and RSP2 Pro are otherwise identical
The RSP2 and RSP2 Pro 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.
The RSP2 series has the same frequency coverage as the RSP1A. Of course, to most of us, the big upgrade from the SDRplay RSP1A is the RSP2’s multiple antenna ports: 2 x 50-Ohms and one High-Z port for lower frequencies.
The SDRplay RSP2 with plastic enclosure.
As with all of SDRplay’s SDRs, their own application, SDRuno, will support up to 16 individual receivers in any 10 MHz slice of spectrum.
Bottom line? Since the RSP2 has multiple antenna ports––and two antenna options for HF frequencies and below–the RSP2 is my choice sub-$200 SDR to use as a transceiver panadapter. (Spoiler alert: you’ll also want to check out our summary of the recently released $279 RSPduo from SDRplay in this review or in Part 3 of our primer before pulling the trigger on the purchase of an RSP2 or, especially, an RSP2 Pro!)
Sometimes big surprises come in small packages. That pretty much sums up the imminently pocketable AirSpy HF+ SDR.
The HF+ has the footprint of a typical business card, and is about as thick as a smartphone. Despite this, it’s a heavy little receiver––no doubt due to its metal alloy case/enclosure.
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 is performance-packed!
Not to dwell on its size, but other than my RTL-SDR dongle, it’s by far the smallest SDR I’ve ever tested. Yet it sports two SMA antenna inputs: one for HF, one for VHF.
The HF port is labeled as “H” and the VHF port as “V”
When I first put it on the air, my expectations were low. But I quickly discovered that the HF+ belies its size, and is truly one of the hottest sub $500 receivers on the market! Its HF performance is nothing short of phenomenal.
The HF+ is not a wideband receiver like the FunCube Dongle Pro+ or RSP series by SDRplay. Rather, the HF+ covers between 9 kHz to 31 MHz and from 60 to 260 MHz only; while this is a relatively small portion of the spectrum when compared with its competitors, this was a strategic choice by AirSpy. As AirSpy’s president, Youssef Touil, told me,“The main purpose of the HF+ is [to have] the best possible performance on HF at an affordable price.”
Mission accomplished. Like other SDRs, the HF+ uses high dynamic range ADCs and front-ends but enhances the receiver’s frequency agility by using high-performance passive mixers with a robust polyphase harmonic rejection structure. The HF+ was designed for a high dynamic range, thus it is the best sub-$200 I’ve tested for strong signal handling capability on the HF bands.
You can very easily experiment and customize the HF+ as well; easy access to the R3 position on the circuit board allows you to make one of several published modifications. “During the early phases of the design,” Yousef explains, “R3 was a placeholder for a 0 ohms resistor that allows experimenters to customize the input impedance.” He goes on to provide in-depth clarification about these mods:
A 300 pF capacitor will naturally filter the LW/MW bands for better performance in the HAM bands
A 10µH inductor would allow the use of electrically short antennas (E-Field probes) for MW and LW
A short (or high value capacitor) would get you the nominal 50 ohms impedance over the entire band, but then it’s the responsibility of the user to make sure his antenna has the right gain at the right band
A custom filter can also be inserted between the SMA and the tuner block if so desired.”
Since the introduction of the HF+, it has been my recommended sub-$200 receiver for HF enthusiasts. If you want to explore frequencies higher than 260 MHz, you’ll have to look elsewhere. Also, note that longwave reception is not the HF+’s strong suit––although modifications to R3 and future firmware upgrades might help with this! Additionally, the HF+’s working bandwidth is 660 kHz; quite narrow, when compared with the RSP series, which can be widened to 10 MHz.
AirSpy also designed the free application SDR# to take full advantage of their receivers’ features and performance.
If you haven’t gathered this already, it’s simply a brilliant time to be a budget-minded radio enthusiast. Only a few years ago, there were few, if any, enthusiast-grade sub-$200 SDR options on the market. Now there are quite a number, and their performance characteristics are likely to impress even the hardest-core weak-signal DXer.
Still, some hams and SW listeners reading this article will no doubt live in a tougher RF environment where built-in hardware filters are requisite to prevent your receiver from overloading. Or perhaps you desire truly uncompromising benchmark performance from your SDR. If either is the case, you may need to invest a little more of your radio funds in an SDR to get exactly what you want…and that’s exactly where I’ll take you November in the final Part Three of this SDR primer series. Stay tuned!
Stay tuned for more in Part Three (November).I’ll add links here after publication.
Many thanks to SWLing Post contributor, Gary DeBock, for sharing the following guest post:
Supercharging the XHDATA D-808
Installation of High Performance AM and LW Loopsticks
By Gary DeBock, Puyallup, WA, USA, September 2018
As a stock receiver the Chinese-made D-808 AM-LW-FM-SW-AIR portable is a very capable performer, with AM reception superior to that of any current Ultralight model, and impressive FM reception as well. The radio was certainly “inspired” (to use a generous term) by the C.Crane Skywave SSB model, which coincidentally was manufactured in the same part of China by C.Crane’s Redsun partner—with the first units going out the door a few months before the D-808 came into existence.
Because foreign intellectual property is routinely copied in China with no punishment from the government, XHDATA essentially had the chance to copy all the good points in the Skywave SSB design and improve upon its weak points as well. The only precaution that XHDATA took after this wholesale design appropriation was to forbid direct shipments of the D-808 from China to North America—presumably to avoid a copyright lawsuit by C.Crane. As such, the first D-808 models were sold to the rest of the world around January of 2018 at a price about half that of the Skywave SSB, while North American DXers were told that since the model couldn’t be shipped to the USA or Canada, they were out of luck.
Of course some D-808 models did make it into North America, where it was found to be a very capable portable with astonishing value for the price. Finally around March, an enterprising Chinese eBay seller came up with a plan to ship the model to North America through Israel, thereby skirting around XHDATA’s direct shipment prohibition. As of late August this eBay seller (harelan ecommerce) has already sold 62 of the D-808 models this way, even though he charges a premium for shipment to North America. Whether this single supply source will continue to serve North American customers is currently unknown, but out of the 7 models that I have purchased from him there hasn’t been a single D-808 model with any issues– despite the apparent lack of any manufacturer’s warranty offered on the radio.
Despite the D-808’s rather dubious design pedigree there is no doubt that the Chinese engineers (or reverse engineers?) did a superb job in creating an awesome radio for the money. Besides directly copying the Skywave’s SSB design and controls, XHDATA also made significant improvements, including a longer loopstick (providing clearly superior AM sensitivity), a much more powerful audio amplifier (correcting a serious shortcoming in the Skywave SSB) and a much lower price (about half that of the $169.99 Skywave SSB, for models shipped outside North America). Another great advantage for someone wishing to perform this loopstick upgrade are the perfectly located, highly accessible Litz wire connections on the RF circuit board—apparently used by the Chinese engineers to conveniently test out various loopsticks, and retained in the final product. The radio’s high quality construction and survivability in adverse conditions were proven repeatedly over the summer here, with the model surviving accidental exposure to a 104 degree (43 degrees C) car trunk temperature, exposure to moderate rain, repeated travel bumps, and use as the main receiver during a 9-day DXpedition to a plunging ocean side cliff in Oregon state. The 3.7v lithium-ion rechargeable battery provides superior run time for extended DXing sessions, and is included in the D-808 shipping package, along with a USB cord to charge the battery, a plug-in wire antenna (for FM,SW and AIR), a vinyl carrying case, and a pretty basic English instruction manual.
One thing you will NOT find supplied with the D-808 is a warranty card– either in the shipping box, or online. This is pretty standard practice in China, incidentally, where concepts like refunds and warranties aren’t generally part of customers’ expectations. This doesn’t necessarily mean that XHDATA won’t repair obvious problems in a new D-808, but it does mean that they aren’t assuming the obligation to do so. I have heard from one North American purchaser who received a new D-808 with a defective speaker, and he is still waiting for the model to be repaired (after paying the shipping charge to send it back to China). Each individual purchaser must decide whether or not this lack of any warranty is a deal breaker. But if you are looking for a final reason to perform this loopstick transplant, why not consider the fact that you will not be violating any manufacturer’s warranty by doing so??
Although this 7.5” loopstick upgrade will certainly make your D-808 far more sensitive than the stock model on Medium Wave or Longwave, it is not designed to compete with large (2’ sided or larger) inductively coupled box loops, or any of the new FSL antennas. The sensitivity upgrade will boost the D-808’s MW band weak-signal performance up to the level of classic portables like the ICF-2010 and RF-2200; however, and since the D-808’s DSP-enhanced selectivity will generally exceed that offered by these classic portables, the overall DXing capability in the AM mode could be considered slightly greater. The D-808 does have SSB capability, although it lacks the SSB tuning convenience offered by the ICF-2010 and RF-2200. It also lacks the ICF-2010’s superb Synch detector, a big advantage in weak signal DXing. But in portability, versatility and DXing value for the price, the “Supercharged” D-808 is a real winner.
This construction article will provide the builder with step-by-step instructions to upgrade the XHDATA D-808’s loopstick to a much more sensitive, externally-mounted 7.5” Medium Wave or Longwave loopstick replacement. Both the Medium Wave and Longwave 7.5” loopstick designs have been thoroughly tested and proven effective in actual DXing by hobbyists other than the author, and as long as the instructions are followed carefully, this relatively inexpensive modification will provide a major improvement in the D-808’s weak-signal reception capability.
This modification project involves close-order soldering on the D-808’s circuit board, and should only be attempted by builders with reasonably good eyesight, good hand coordination and soldering experience. The project also calls for the use of a precut plastic loopstick frame to attach the antenna to the top of the D-808’s top back cabinet surface, and the construction of this precut plastic frame requires either the use of a 12” (or larger) power miter saw, or some rather lengthy cutting with a hacksaw. Use of a power miter saw SHOULD NOT be attempted by those without serious power tool experience! The author assumes that only qualified power tool operators will attempt to use a 12” miter saw to cut these frames quickly, and that other builders who wish to construct them will use a hacksaw. As such, only basic cutting instructions are provided for the 12” power miter saw users, while detailed instructions are provided for the hacksaw users. To assist builders who are not qualified to use power tools, the author has prepared a LIMITED number of these precut plastic loopstick frames on a power miter saw, which will be offered at cost to these builders on a first come, first served basis.
A final warning is in order concerning the step of gluing the precut plastic loopstick frame to the D-808’s top back cabinet surface. Although this step is not dangerous, it is pretty tricky. Since the superglue “grips” very rapidly, you will only get one chance to ensure that the frame is straight, and centered on the D-808’s top cabinet surface. Do yourself a favor, and make multiple “dry runs” to practice this important step before applying the glue! Failure to take this step seriously will probably result in a crooked loopstick frame—which will hold the antenna just fine for DXing purposes, but which will be an eternal reminder to the DXer (and everyone else) of the hazards of haste.
Construction Parts Required
This 7.5” loopstick D-808 construction article will guide you through the assembly of either a 7.5” Medium Wave loopstick D-808 or a 7.5” Longwave loopstick D-808, so make sure that you order the parts necessary for construction of your chosen model. The picture above shows the parts that will be necessary for construction of either model, but the Litz wire and 7.5” ferrite rod components differ according to whether you are building the Medium Wave or Longwave model.
Miscellaneous: One packet of Duro Super Glue (.07 ounce size), solder, 25w (low heat) soldering iron, hacksaw (or power miter saw), screwdriver set, sandpaper, needle nose pliers, diagonal cutters
D-808 Radio Preparation
Before starting the modification give the radio a thorough test on all bands, ensuring that all the stock model functions work properly, and that there are no issues with the display, speaker, headphone jack, battery or charging system. It’s also a good idea to run a daytime DX band scan on the AM or Longwave band (for whichever band you plan to construct an upgrade loopstick) and document the results—to use as a benchmark for the upgrade loopstick’s performance.
Antenna Frame and 7.5 inch Loopstick Preparation
1) Refer to the photo below. Using the “Supercharging the Tecsun PL-380” article (posted at http://www.mediafire.com/file/du3sr5cd9thqvau/7.5inch-LS-PL380.doc/file or available directly from the author) carefully prepare the orange loopstick antenna frame according to construction steps 1-9, EXCEPT note that the lower (glue surface) edge of the antenna frame should be cut to a length of 5 3/4” (147mm), NOT 5” (127mm) as described in the PL-380 transplant article. Pay close attention to the safety precautions concerning power tool usage, and DO NOT attempt to use a power miter saw unless you have SERIOUS power tool experience!
2) If you are constructing an AM (Medium Wave) loopstick, follow construction steps 10-16 in the PL-380 transplant article to construct the antenna. If you are constructing a Longwave loopstick, follow construction steps 10a-16a in the PL-380 transplant article to construct the antenna. If you are constructing both loopsticks, MAKE SURE that the ferrite rod and Litz wire are only used in the antennas for which they were designed. Mixing up these items is very easy, and such a mistake will make both loopsticks perform like clunkers.
3) After construction of either the AM or Longwave loopstick, follow the instructions in steps 29 and 30 of the PL-380 transplant article to install a piece of 3 1/8” (79mm) shrink tubing, EXCEPT note that this length is slightly longer than the 3” (76mm) length called for in the PL-380 article.
4) Refer to the photo below for the following three steps. [NOTE: Although this photo shows the AM (Medium Wave) loopstick, the procedures in this step are the same for the Longwave loopstick, although the position of the rubber hose lengths and clear vinyl inserts will be closer to the ends of the ferrite rod]. Carefully slide the length of 3 1/8” shrink tubing into the position shown, ensuring that there are no Litz wire kinks or bends inside the shrink tubing.
5) Take the two 3/4” (19mm) clear vinyl inserts and slide them onto the ferrite rod ends, twisting them up against the border of the Scotch “Extreme” tape ends to lock the tape in place under the vinyl inserts. Ensure that the clear vinyl inserts do not touch any Litz wire leads or coil turns.
6) Slide the 1” (25mm) lengths of rubber heater hose over the clear vinyl inserts until the appearance of the loopstick resembles the above photo. Ensure that the rubber hose sections also do not touch either the Litz wire leads or any coil turns. Finally, place the completed loopstick in a safe place until it is called for in Step .
7) Refer to the photo above for this step. Remove the battery from the radio, and using a Jeweler’s Phillips screwdriver of the correct size, remove the six identical screws in the positions shown (NOTE: These screws have a tendency to stick inside their slots, even when the slots are turned upside down. If you cannot remove all six screws it’s not a major problem, but at least ensure that the screws are completely loose in their slots, and that you don’t lose any of them during the remaining steps). Grasp the tuning knob, and pull it out horizontally in a completely straight manner to remove it from the radio. Ensure that the battery, tuning knob and all removed screws are placed in a safe place until the radio is reassembled.
8) Carefully separate the front and back cabinet sections and place them down in the position shown in the photo below. Note that the front and back sections of the radio are connected by a ribbon wire plug-in system– ensure that this plug remains securely inside its slot at all times, and that no great stress is placed on the speaker wires.
9) Refer to the close up photo below, and note the position of the two Litz wire soldering points on the circuit board (in the lower right corner of the photo). Using diagonal cutters, cut the two Litz wire leads at the position shown, UNLESS you wish to salvage this stock loopstick for other projects—in which case you should desolder the entire lengths of the Litz wire leads from the circuit board at the positions shown in the lower right corner (NOTE: The stock loopstick is of a fairly good design, and has an inductance that would be compatible with any DSP-chip Ultralight radio, providing an AM sensitivity boost in the process).
10) Refer to the photo below. Using a flat Jeweler’s screwdriver with a 1/16” blade, carefully probe around all four sides of the stock loopstick to break all of the glue bonds. Work slowly and carefully around the perimeter of the ferrite rod, including the plastic covers on each end. Once most of the glue bonds have been broken the ferrite rod will begin to shift around as you break up the few remaining bonds, but until this point work slowly and patiently to break up the glue.
11) Refer to the photo below. Using the flat Jeweler’s screwdriver, once all of the glue bonds have been broken and the ferrite rod is loose in its slot, lift the ferrite rod out of its slot on one side by prying up under the plastic cover on the end of the ferrite rod. Ensure that the Litz wire leads have either been cut or desoldered from the circuit board, then grasp the ferrite rod with your fingers and pull it completely out of the slot with a slight twisting motion.
12) Remove the wrist strap, and refer to the photo below. Carefully pick up the two sides of the radio and place the back section in a vertical position as shown, with a heavy flat weight (barbell, or other heavy flat item) pressing up against the back cabinet section to keep it in a vertical position. Ensure that there is adequate, even lighting on the top cabinet section for the gluing process in the next step, and that the back cabinet surface will not shift around as you make the gluing “dry runs,” and perform the actual gluing of the loopstick frame to the top of the cabinet.
13) Take the previously prepared orange plastic loopstick frame, and ensure that its bottom glue surface is completely smooth and flat, with no uneven ridges on the edges of the glue surface (remove these with fine sandpaper, but ONLY on the ridges, and not on the rest of the flat glue surface). Using a damp paper towel, wipe the top cabinet glue surface and the loopstick frame glue surface to remove any dust or debris, then wipe them again with a dry, clean paper towel to ensure that they are both completely dry.
Take the loopstick frame and gently slide the frame over the top cabinet surface to ensure that both surfaces are smooth and flat. Refer to the photo at the top of the next page. Ensure that there is even, bright lighting on the top cabinet surface, and make several “dry runs” to place the loopstick frame in the exact center of the top cabinet surface (with 1/16”, or 1.5mm of space between the frame ends to the cabinet ends), and also 1/16” (1.5mm) of overhang above the front edge of the cabinet’s glue surface (NOTE: if you wish to simplify the process by lining up the front edge of the loopstick frame with the front edge of the cabinet’s glue surface it will still provide an acceptable result, but you will need to do some minor sanding of the whip antenna’s plastic slot post, as shown in the photo below. In either case, make repeated “dry runs” with the loopstick frame to practice placing it in the exact center of the top cabinet’s glue surface, since you will only get one chance to place it in the proper center position once the superglue is applied.
NOTE: The back of the loopstick frame has a beveled surface to permit full operation of the radio’s whip antenna after the frame is glued on the top of the cabinet surface. If the loopstick frame is glued with a 1/16” (1.5mm) overhang in front of the front edge of the cabinet surface then the whip antenna should have enough space for free operation. The alternative is to glue the two front edges lined up with each other to simplify the gluing process, in which case minor sanding may be required on the whip antenna slot post, as shown in the photo below.
14) After making multiple “dry runs” and becoming familiar with accurate placement of the loopstick frame on top of the cabinet, refer to the photo at the top of the next page. After once again ensuring that the back cabinet section will not shift around during the gluing process, take the Duro superglue packet and apply a thin (1/8”, or 3mm) bead of glue along the center of the cabinet’s glue surface, extending it 5 1/4” (133mm)long, with equal spaces on both ends (as shown). While sighting the two sides place the loopstick frame carefully down in the correct center position as practiced previously, with the 1/16” overhang if desired. If satisfied with the position, press down on the frame to lock the two surfaces together securely. Usually the frame may be shifted around slightly within 1 or 2 seconds of placing it on the superglue, so use this brief time to promptly shift the frame to a straight position, if necessary. After a couple of seconds, though, you will need to be satisfied with whatever position the frame has ended up with (regardless, it will still hold the loopstick just fine, for DXing purposes).
15) After the loopstick frame is securely placed and locked on top of the D-808’s cabinet surface, place downward pressure on the loopstick frame along its length in order to ensure a tight glue bond throughout the entire top cabinet surface. Continue this process for about one minute, and sight both ends of the loopstick frame to ensure that they are both completely flat against the D-808 cabinet.
16) Inspect the front and back edges of the loopstick frame’s border with the D-808 cabinet for any glue seepage, and if any is found, remove it promptly with the 1/16” flat Jeweler’s screwdriver blade. Glue should not be allowed to run past the frame edges. This completes the process of gluing the frame to the D-808 cabinet.
7.5” Loopstick Installation
17) [NOTE: The installation procedures of the Medium Wave (AM) and Longwave loopsticks are identical, except that the plastic tie wraps and rubber hose sections are closer to the ends of the ferrite rod in the Longwave version. The following photos are for the Medium Wave (AM) version, but Longwave loopstick builders should follow the same steps, while referring to the Longwave model photo in the “Operation” section as a guide]
Refer to the photo below. Carefully take the previously prepared 7.5” loopstick and hold it in the position shown—in its slot, centered in the middle of the orange antenna frame, with the shrink tubing and Litz wire leads running down to the left. Take the two plastic tie wraps and install them in the position shown, centered over the rubber hose sections on the loopstick, while ensuring that no Litz wires or shrink tubing is bound under the plastic tie wraps.
18) Refer to the photo below. Lay the two cabinet sections down flat as shown, ensuring that the Litz wire shrink tubing is in the exact position shown (if it isn’t, carefully slide it along both Litz wires until it is in this exact position). Carefully thread one Litz wire end through the empty wrist strap hole, then thread the other Litz wire end through the hole, as shown. Finally pull on the two Litz wires together from the right while guiding the end of the shrink tubing into the empty wrist strap hole, and pull a short section of the shrink tubing through the hole (as shown) to protect the Litz wire insulation from friction damage.
19) Refer to the photo below. Using the previous procedure to install shrink tubing (which is described in the PL-380 transplant article) install a 2.5” (63mm) length of shrink tubing over the two Litz wire ends, and shift the shrink tubing into the position shown in the photo. After this is done cut the two Litz wire leads to the lengths shown in the photo (NOTE: make sure that the ends of both Litz wires are cleanly cut, not frayed and at the minimum diameter before attempting to insert them into the shrink tubing. The process is much easier when the Litz wires pass smoothly through the shrink tubing).
20) Refer to the close up photo below. Using a low heat (25w) pencil-type soldering iron, remove the two stock Litz wire leads at the positions shown, taking care not to use excessive heat, or touch the adjacent components. Ensure that the new Litz wire leads are at the length shown when the leads are in a horizontal position throughout the cabinet, and cut them to this length if they are not.
21) NOTE: When tinning the 250/46 Litz wire it is essential that all of the individual Litz wire strands be completely soldered together for a length of at least 1/4” (6mm), with bright, shiny solder around the circumference of the Litz wire ends for this minimum (1/4”) length. The Litz wire must be heated with a clean, hot soldering iron around its circumference in order to melt the solder properly for this step]
Refer to the photo above. Pull the Litz wires up out of the previous position, and place a clean rag underneath them (on top of the circuit board) to completely protect the circuit board from any solder which might accidentally drop down during the tinning process. Using your hot 25w soldering iron melt a generous amount of solder on its tip, and work the soldering iron tip slowly and patiently around the circumference of each Litz wire end until there is a bright, shiny solder length of at least 1/4” (6mm) in a cylindrical pattern at the end of each Litz wire. When doing this, take great care not to allow any solder to drip down onto the circuit board below (i.e., make sure that your rag completely covers the circuit board). The final appearance of your Litz wire lead ends should resemble those in the photo.
22) When your Litz wire lead ends resemble the photo above, cut the soldered portion down to a length of 3/16” (5mm) and observe the appearance of the end of the Litz wire. It should have a bright, solid circular shape, with no gaps or individual Litz wires showing. If not, reheat the end of the Litz wire while adding some solder, and repeat this step.
23) NOTE: The Litz wire connection points on the circuit board are surrounded by other important components. It is important to avoid solder drips on these components, or solder bridges to their leads. Solder the Litz wire leads down at an angle to avoid these surrounding components, and use the minimum amount of heat and solder to ensure good electrical connections)
Refer to the close up photo above. Following the precautions described, solder the two Litz wire leads down onto the circuit board at an angle, as shown in the photo. After soldering, make a close visual inspection to ensure that there are no solder bridges across the Litz wire connections, or nearby components. The remaining length of the Litz wire leads should be routed in a horizontal manner to the wrist strap hole.
24) Carefully pick up the front and back cabinet sections, and hold the back cabinet section fairly close to the front section (as the radio would normally be oriented, when assembled). Refer to the photo below, and carefully insert the “Fine Tuning” control thumbwheel from the front cabinet section into its slot on the back cabinet section in a sideway movement. This will allow you to fully close the front and back cabinet sections in the next step.
25) Refer to the photo below. Pick up the two cabinet halves and carefully snap them together (this action should not require any great force). Place the radio face down in the position shown (with a soft surface underneath, for protection), and using the Jewelers Phillips screwdriver of the correct size, carefully screw in the six screws that were loosened previously, starting with the screw near the whip antenna post (you should pick up the radio temporarily and hold the two cabinet sections together tightly at this corner, as you do this).
After all six screws have been retightened take the Tuning control knob and press it back onto its shaft in a straight horizontal motion. Finally, reinstall the battery and battery compartment cover to finish up the reassembly.
TESTING AND OPERATION– MEDIUM WAVE MODEL
This 7.5” transplant loopstick is designed to provide a major boost in sensitivity from 530-1700 kHz, and if the antenna is working properly both the weak signal reception and the radio’s nulling capability should be greatly enhanced. It is normal for the antenna to receive more background noise on the low band frequencies, although the sensitivity boost should be substantial across the band.
The construction design of the orange antenna frame allows full usage of the whip antenna for checking SW parallels of MW-DX stations, although if you chose to glue the antenna frame flush with the front of the back cabinet surface to simplify the gluing process, you may need to sand the whip antenna slot post slightly to allow free movement of the whip antenna (see step #13).
In the photo above, some of the important controls for Medium DXing are highlighted. The AM Bandwidth control allows you to choose multiple DSP filtering selections to enhance selectivity as desired, with the narrowest filtering (1 kHz) providing both the sharpest selectivity and the best weak-signal sensitivity. However this 1 kHz setting also has the poorest audio fidelity, with the higher audio frequencies typically cut off by the DSP filtering. As such, for regular DXing far away from strong local pests, the other AM Bandwidth settings may be more suitable. The Direct Frequency Entry key allows you to manual enter in any MW frequency, to which the radio will shift once the numbers are pressed on the keypad. The Tuning knob has three different modes, which can be toggled by pressing the knob horizontally. The first mode is tuning in either 9 kHz or 10 kHz steps (depending on which of these step you have selected), while the second mode is tuning in 1 kHz steps. The third mode is to lock the frequency in place. Pressing the knob again will return the tuning to 9 or 10 kHz steps.
The XHDATA D-808 has multiple display functions, which can be toggled by the indicated key. The first option is the temperature in either Centigrade or Fahrenheit (depending on your pre-set preference), while the second option is the alarm time. The third option is the current time (which you need to set according whether you prefer UTC or local time), while the fourth option is the received signal strength in both dBu and dB.
The supplied 3.7v lithium ion battery has superior run time, and may be easily charged using the supplied USB cable to either a computer or AC outlet (with the appropriate adapter). As reported in various posts throughout this year, the D-808 model has rugged construction with an excellent record of survival under tough conditions, including hot summer days, moderate rain exposure and extended usage as the main receiver during a 9-day ocean cliff DXpedition in Oregon—performing flawlessly at all times.
It is the author’s sincere hope that this “Supercharged” D-808 model will bring you a lot of DXing fun during travel, as well as at other times. When conditions are good you should never underestimate this enhanced model’s potential of receiving awesome DX beyond your expectations—as an example, here is the stand-alone performance of a 7.5” loopstick D-808 in receiving 1017-A3Z in Nuku’alofa, Tonga (10 kW at 5,632 miles/ 9,063 km) on the ocean cliff near Manzanita, Oregon at 1301 UTC on August 8th of this year:
Not only Tonga is received, but even the Australian horse racing station 1017-2KY in Sydney (5 kW at 7,630 miles/ 12,280 km) is received as a weak co-channel in the middle of the recording. My hope is that you all will be so lucky with your new Supercharged D-808!
73 and Good DX,
Gary DeBock (in Puyallup, WA, USA)
Absolutely amazing! Thank you for taking the time to put this procedure together and describing the process in such fine detail, Gary! Hats off to you!
Click here to read all of Gary DeBock’s posts on the SWLing Post.
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?”
“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 andsoftware. 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:
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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!
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.
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.
Many thanks to SWLing Post contributor, TomL, who shares the following guest post:
Backpack Shack 3 – Amplified Whip Antenna
So, having enjoyed using the Ferrite Sleeve Loop I created last year, I have wanted something a little more sensitive and less bulky. I will eventually create a much BIGGER FSL antenna on the order of 2 feet long and perhaps 18 or 24 inches in diameter for indoor/attic use. But that is not a priority at the moment.
Since I already have the DX Engineering Pre-Amplifier and the very nice Cross Country Preselector from the loop project, I thought it might be useful to create an active whip antenna for it. And the cool looking Solar Red backpack needed something to do!
Now that the bulky loop was not taking up the main compartment of the backpack, I could think about what else to put in there, like a larger power pack. I scoured FleaBay for ideas and stumbled upon this contraption for backup power to network systems, the CyberPower CyberShield for Verizon.
This has 12 spaces for D-cell batteries and was mounted inside the demarcation terminal to provide backup power for things like cable systems and Copper-to-Ethernet networks. It is not waterproof, so would be inside the premises of the customer getting the internet/cable service. But my Pre-Amp needs 12-18Volts and would love to have nearly unlimited power. So, I bought a used one, cut the end off of the power lead and put on my own 2.1×5.5mm plug (carefully glued down and tie-wrapped). Then I filled it with 1.2Volt Tenergy D-cells.
Everything was just fine until I forgot to double check the polarity of the plug that I had wired onto the end. Plugged it into the DX Engineering Pre-Amp, flipped the power switch and fitzzz…. The Pre-Amp light went on, then off (permanently!).
So, my expensive mistake is that I start using the FREE multimeter I got from Harbor Freight and check the polarity before I connect homemade battery packs to anything!!
DX Engineering charged me $60 to fix my mistake and it is working fine now after I swapped the wires on the plug. Yes, their Pre-Amp is NOT reverse-polarity protected! Disappointing, since the price tag for that device is $148!!! The CyberShield now sits comfortably inside the bottom of the backpack.
Now that the drama was over regarding the Power pack, I could think about the whip. I did not want a wimpy whip! (No one should rightly aspire to this, in my opinion). More FleaBay searches found me looking at Trucker parts. Loaded whips, magnetic mounts, 10 foot tall MFJ telescoping whips, etc was looking a bit expensive.
Besides that, I cannot fit a 10 foot tall telescoping whip into the backpack, I am limited to at most 18 inches (and that is at an angle to fit it in there). But I found an old-fashioned mirror mount that looked promising since it had a nice SO-239 connector at the bottom and standard CB antenna fitting on top of 3/8”-24.
Then I found the 44 inch SuperAntenna with the same threads; then found the replacement Stainless Steel Shafts for a Wilson antenna in different lengths (I ordered the 10 inch version to test). With a couple of rod coupling nuts and I was ready for testing!
I had already scheduled a short vacation to Sleeping Bear Dunes on the thumb of Northwestern Michigan, so I took this test setup with my Sony ICF-2010. This area is a very nice remote National Lakeshore with minimal noise. I tried a beach setting and a couple of hilltop picnic areas (including meeting a local Porcupine) and had very nice reception at all locations. The hilltop locations are approximately 400 – 600 feet above the Lake (yes, the Dunes are THAT big there!).
Meeting a local Porcupine
Later on, I went to Grand Haven, MI on the way home and stopped at their very lovely beach.
Reception was just as good as the hilltop locations at Sleeping Bear! In both areas, I was next to a large body of water (in this case, Lake Michigan) and makes for an advantageous place for DXing! I had also stopped at a Rest Area off the highway and that was a terrible place even though it was electrically quiet but nowhere near the big Lake. I guess the rumors are true about being near a large body of water somehow enhances reception of weak signals–?
I will submit recordings later since I lost the mini-B cable for the Sony digital recorder and had to order a replacement. However, this was a nice project that freed up some space inside the backpack. I will add an 18 inch extension to the whip that will give me a total length of 72 inches. Plus, it is mounted 12 inches up on the poly cutting board and I place the backpack on a small hunters folding chair that is about 24 inches tall. So, the tip will be about 9 feet off the ground.
Not pictured but I was also able to easily fit inside a used CCrane Twin Coil Ferrite antenna for mediumwave use that also performed very well. I noticed that the picnic benches at some locations are made of metal, so that gives me a future idea of trying to leverage that to use as a ground plane somehow. The battery pack is heavy but also gives great ballast to the backpack and will not tip over. Cannot wait for the Tecsun S-8800 to arrive so I can try leaving the radio inside the bag and just use the remote control to tune!
As always, I’m so impressed with your spirit of radio adventure, Tom! I love the fact that your goal is to make a field-deployable DX kit that isn’t cumbersome or time-consuming to set up on site. I imagine you only need a couple of minutes to open the pack and have it on the air.
Those DXing spots are stunning! I had no idea one could find 400-600′ dunes in NW Michigan–! With that said, I’ve heard that part of the state is one of exceptional natural beauty. If you could somehow turn the lake into a body of salt water–thus increasing ground conductivity–you’d really enhance that already impressive reception! I’m guessing that sort of project would be a bit outside your budget! Ha ha! That and the freshwater fish might protest!
To me, there is no better way to enjoy radio than finding a nice RF quiet spot in the great outdoors…no matter where you live in the world. On top of that, Tom, you’re constantly building, experimenting, documenting and sharing your findings–you’re a true radio zealot! Huzzah!
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