Many thanks to SWLing Post contributor, Ivan (NO2CW), who writes:
I ran a test of weak signals RTL-SDR v4 against Airspy HF+ Discovery. Using sdr # and a few gain adjustments particular to each of the receivers. I ran the test at approximately 9 pm local time using the same W6LVP loop antenna from my location near Miami Florida and I was intentionally looking for barely readable weak signals. The RTL-SDR v4 is a great budget SDR receiver!
Many thanks to SWLing Post contributor, Mario Filippi (N2HUN), who shares the following guest post:
Author’s Airspy HF+ Discovery (small black box to the left of the laptop)
by Mario Filippi (N2HUN)
I recently purchased an AirSpy HF+ Discovery. As a SWL for over 60 years who’s owned many shortwave radios by manufacturers such as Drake, Yaesu, Icom, Zenith, Kenwood, Panasonic, Sony, Radio Shack, Grundig, CountyComm, MFJ, Sears, AOR and have used a number of different SDRs such as the RTL-SDR.com, HackRF, NooElec and many other rudimentary inexpensive first generation SDR dongles, I feel the AirSpy was an excellent choice. It cost $169 plus shipping.
For LW/MW/HF reception, I use a 30’ ground mounted vertical with about 50 buried radials in different stages of decomposition hihi. For VHF, a roof mounted 2m/70cm SlimJim antenna is used, but I haven’t done much listening in that portion of the spectrum yet except for occasional foray into the aero, 2m ham, NOAA satellite and public service bands. Note that the AirSpy also covers 60 – 260MHz.
An older Dell Inspiron laptop and SDR# are used in conjunction with the AirSpy. For decoding, MultiPSK, FLDigi, MTTY, Yand (for NAVTEX), along with VB cable are the accompanying software to make the digital modes intelligible.
So far I’ve logged a few local LF aeronautical beacons and some DGPS beacons on longwave but will be in a better position to judge its performance when winter sets in. As for the medium (520 – 1710 kHz) wave AM broadcast band, the AirSpy easily brings in both local stations during daytime and distant stations at night with no adjacent channel interference whatsoever. Even low powered community Emergency Alert Stations in the 1600 – 1710 kHz portion of the band can be heard daily from this QTH. A rotatable loop would certainly improve reception though.
As for shortwave listening the AirSpy HF+Discovery is, in my opinion, great for listening to both shortwave broadcasts and utility stations though I tend to concentrate on UTES mostly such as VOLMET, WEFAX, RTTY (the few that remain unencrypted), CW marker stations (e.g. XSG and XSQ from China) NAVTEX (519 kHz), aero/maritime SSB, time signal stations (WWV, CHU) and many of the other esoteric digital utility signals populating the band. As for SW broadcast stations, WRMI, Radio Exterior, RFI, R. Marti, BBC, WWCR and Radio Algerienne, to mention a few have been received. The Frequency Manager (memory storage) in SDR# has quickly filled up with intercepts using the AirSpy.
As a ham and CB operator (yes, the two can mutually coexist in the same human body), I’ve found the AirSpy HF+ Discovery to be a trouper on all the HF ham and CB bands. One of my favorite hangouts is the 28.100 – 28.300 MHz slice of 10m where domestic and international low power CW beacons transmit their callsigns (and at times their grid squares and power output) into the ionosphere and achieve great distances. Recently, beacons from 5, 6 and 7 land in the US along with DX prefixes ED4, PY4 and XE1 were logged. If you’re into 10m FM operation you can also tune the AirSpy to hear local and distant repeaters on 29.62 – 29.68 MHz. When the band is open, .62 and .64 seem to be the most active here in Central NJ.
If you’re a CB (aptly named the Citizen’s Band) op, the AirSpy HF+ Discovery does a stellar job on Channels 1 – 40 which is especially exciting when the band’s open. While domestic (USA) CB’ers are limited to frequencies from 26.965 – 27.405 MHz you’ll nonetheless hear DX ops below our (USA) channel 1 and above channel 40 conversing in French, Spanish and German in LSB/USB. Add to this mix the fact that the FCC dropped the 150 mile limit for US ops a few years back and now the advent of the FM mode operation in the US, you’ll find the AirSpy won’t disappoint. In my opinion the AirSpy HF+Discovery was an excellent choice and I’m more than satisfied with its performance.
In the matter of honesty and full disclosure, I purchased the AirSpy HF+ Discovery completely on my own in an effort to upgrade my station. My choice was based on information gathered from the Internet and YouTube video reviews. The performance of this receiver was based on my experience using the vertical antenna described earlier, the hours spent at my QTH (location) listening to stations of interest to me and my six decades experience as a SWL. No test equipment to assess sensitivity, selectivity or other empirical methods to measure performance was used. That information can be found on the Airspy website. The main purpose of this article was to craft a rudimentary review for those interested with the caveat that reception will vary depending on many factors such as location, antenna, ionospheric conditions, feedline quality, computer/software variations, QRN, QRM, and operator experience. The results presented in this article are typical for my location; others may experience different results. Thanks very much.
Many thanks to SWLing Post contributor, Bill Hemphill, who shares the following guest post:
YouLoop Antenna Funby Billy Hemphill WD9EQD
Like many listeners, I live in an antenna restricted community. While I have strung up some hidden outdoor wire antennas, I have found that they didn’t really perform that much better than just using the telescoping antenna with maybe a length of wire attached. The biggest problem (whether indoor or outdoor antenna) has been the high noise floor.
A few months ago I bought an AirSpy HF+ Discovery SDR receiver. I had already owned a couple of SDRPlay SDR receivers, but the high noise floor limited their performance. I had read good reviews about the AirSpy, especially its performance on the AM Broadcast band and the lower shortwave bands.
I have about 80 feet of speaker wire strung from the second floor and across the high windows in the living room. This does perform fairly well, but the high noise floor still exists.
A couple of weeks ago, I bought the YouLoop Magnetic Loop antenna from AirSpy. I gave it a try and am amazed at the lower noise floor compared to the indoor wire antenna.
AirSpy with Wire Antenna
AirSpy with YouLoop
AirSpy with Wire Antenna
AirSpy with YouLoop
AirSpy with Wire Antenna
AirSpy with YouLoop
Dramatic reduction in the noise floor. I’ve done a lot of playing around with it and find that the YouLoop picks up just about the same stations as the indoor wire antenna does. But with the lower noise level, the YouLoop makes it more enjoyable to listen. Overall, the YouLoop is now my main antenna.
It works so well with the AirSpy, I started wondering if I could use it with a portable radio, like the Tecsun PL-880. But the AirSpy website has the following note:
Note: It is very likely your third party radio will not be sensitive enough to operate with the YouLoop properly. We have even seen self-documented failed attempts to build pre-amplifiers to compensate for the lack of sensitivity and/or the required dynamic range in third party radios. Use your brain, and eventually an Airspy HF+ Discovery.
Doesn’t sound like it will work with portable radios. BUT, I’m always one to try anyway.
Tecsun PL-880
Since the YouLoop has a SMA connector, I bought a SMA to 1/8” phone jack cable. Plugged it into the PL-880 antenna jack and found I had almost a dead radio. Very few stations heard. But in playing around, I accidentally touched the phone plug to the telescoping antenna and instantly got strong signals.
I did some very unscientific tests. I attached the YouLoop through the side antenna jack, did an ATS scan, then did the same with the YouLoop clipped to the telescoping antenna. Also did a scan with just the telescoping antenna fully extended.. I got some very interesting results. These were done one after the other, so there can be differences in signal fading, etc.
I have repeated the above test several times at different hours. While the actual number of ATS stations varied, the ratio between them remained fairly consistent to the above numbers.
From the above, it appears that the telescoping antenna circuit is more sensitive than the 1/8” antenna jack circuit. Maybe some attenuation is being added to the 1/8” jack since it’s more likely a higher gain antenna would be used there. Can anyone confirm that the circuit indeed attenuates thru the antenna jack?
The YouLoop seems to be a decent performer when directly clipped to the telescoping antenna. While not as good as a high gain outdoor antenna would be, it definitely is usable for indoor uses.
I also tested it clipped to the antennas of some other portable receivers. Tecsun S-8800, PL-330, Panasonic RF-2200 and Philco T-9 Trans-World receivers. All showed an increase over just using the telescoping antenna.
Some interesting notes:
The Tecsun PL-330 saw the same reduction in signal when directly plugged into the antenna jack as opposed to clipping on the telescoping antenna.
The Tecsun S-8800 did not show that much of a drop. I basically got the same number of stations when clipped to antenna as when I connected to the BNC jack:
In conclusion, I find that I can use the YouLoop with my portable radios to increase the signals on strong stations when used indoors. And it is quite the performer when used with the AirSpy HF+ Discovery SDR receiver. It easily portable and I find that I move it around the house as I need to. I just hang it off a window curtain rod. I may just order a second one so that my family room radio has one permanently attached to it.
This morning, I’m looking at the calendar and I see and end in sight for 2020. I think most of us can agree that 2020 will be one for the history books, in large part due to the Covid-19 global pandemic which has had a pretty dramatic affect on many of our lives. It certainly brough my planned travels to a halt. I think many of us are quite happy to show 2020 the door!
As each year comes to a conclusion, I often look back at my radio activities during that year and see how it played out. I especially note the radios I used most heavily throughout the year.
Since I evaluate and test radios, models that are new to the market obviously get a lot of air time. Still, I’m also known to pull radios from the closet and give them some serous air time.
I’m very curious what radios you gave the most air time in 2020?
Here’s my list based on type/application:
Since they’re new to the market, both the Tecsun PL-990 (above) and Belka DX (below) got a lot of air time.
I do like both radios and even took the pair on vacation recently even though packing space was very limited. I see the Belka DX getting much more air time in the future because 1.) it’s a performer (golly–just check out 13dka’s review of the Belka DSP) and 2.) it’s incredibly compact. The Belka now lives in my EDC bag, so is with me for impromptu listening and DXing sessions.
A classic solid-state portable that also got a lot of air time this year was the Panasonic RF-B65. Not only is it a performer, but it has a “cool” factor that’s hard to describe. I love it.
In a sense, the C.Crane CCradio3 got more play time than any of my radios. It sits in a corner of our living area where we tune to FM, AM and weather radio–90% of the time, though, it’s either in AUX mode playing audio piped from my SiriusXM receiver, or in Bluetooth mode playing from one of our phones, tables, or computers. In October, the prototype CCRadio Solar took over SiriusXM duty brilliantly. I’m guessing the CCRadio3 has easily logged 1,600 hours of play time this year.
Of course, the Panasonic RF-2200 is one of my all-time favorite vintage solid-state portables, so it got a significant amount of field time.
While at home the WinRadio Excalibur still gets a large portion of my SDR time, both the AirSpy HF+ Discovery and SDRplay RSP DX dominated this space in 2020.
The HF+ Discovery was my choice receiver for portable SDR DXing and the RSPdx when I wanted make wide bandwidth recordings and venture above VHF frequencies.
Without a doubt the new Mission RGO One 50 watt HF transceiver got the most air time at home and a great deal of field time as well. It’s such a pleasure to use and is a proper performer to boot!
My new-to-me Icom IC-756 Pro, however, has become my always-connected, always-ready-to-pounce home 100W HF transceiver. It now lives above my computer monitor, so within easy reach. Although it’s capable of 100+ watts out, I rarely take it above 10 watts. The 756 Pro has helped me log hundreds of POTA parks and with it, I snagged a “Clean Sweep” and both bonus stations during the annual 13 Colonies event.
The new Icom IC-705 has become one of my favorite portable transceivers. Not only is it the most full-featured transceiver I’ve ever owned, but it’s also a brillant SWLing broadcast receiver. With built-in audio recording, it’s a fabulous field radio.
Still, the Elecraft KX2 remains my choice field radio for its portability, versatility and incredibly compact size. This year, in particular, I’ve had a blast pairing the KX2 with the super-portable Elecraft AX1 antenna for quick field activations. I’ve posted a few field reports on QRPer.com and also a real-time video of an impromptu POTA activation with this combo:
What radios did use use the most this year and why? Did you purchase a new radio this year? Have you ventured into the closet, dusted off a vintage radio and put it on the air?
Listening to Radio Prague via WRMI with the Xiegu GSOC
Many thanks to SWLing Post contributor, Tim R, who writes:
Dear Thomas,
First of all thank you so much for the all of the energy you put into the SWLing Post. When crazy things are happening in the world it’s a very welcome sanctuary! Sending you some coffee money.
I plan to become a ham radio operator next year. Bought the book last week and once I finish a large project for work, I’m on it. Of course, the Tech license will only give me limited exposure to HF, but I’m already plotting an HF radio purchase because I can’t WAIT do do some SWLing with it. Up to this point, I’ve only owned portable radios and never really have used external antennas other than some cheap wire.
My question…
I’ve been considering grabbing a Xiegu G90 because it seems to be a nice comprehensive beginner’s HF rig and is very affordable. I read your review and understand your caveat that there’s no way to completely disengage the transmit so that it can’t be accidently hit if connected to an RX only antenna. I’m not worried about that because I’m going to hang a G5RV wire antenna and use it both for TX and RX. No problem if RF is accidently sent through it.
Of course, there’s a lot of buzz in the Xiegu community about the new GSOC controller. I had not planned to exceed $600 for my radio purchase, but I love the idea of the controller. But when I add $550 for the controller and $450 for the radio, all the sudden I’m at $1,000.
After some deep soul-searching (and let’s be frank here, a blessing from my wife and CFO) I’ve decided to raise my budget to $1,000.
All of this to ask, if you had $1,000, would you buy the G90 and GSOC controller, or would you get something else keeping in mind I want to use this as much for shortwave listening as for future ham radio work?
Any advice would be appreciated.
-Tim
Thanks for your question, Tim! And thanks for giving me a complete picture of your budget/radio requirements and the antenna you plan to use.
I’ll try to answer your question here, but understand this is more what I would do if I were in your shoes. This is a pretty simple question, but not simple to answer because there are so many options on the market.
Keeping in mind, I feel like the GSOC is a work in progress at the moment and not fully developed–check out my initial review. Once the next firmware update is available it could certainly solve a number of small issues I found with the unit. It works, but it’s not a refined product yet.
It’s ironic, actually. When I received your message this morning, Tim, I was SWLing with the GSOC and G90–listening to Radio Prague on WRMI. In the end, though, the GSOC is primarily an enhanced interface for the G90. While it does add some extra functionality (and should, over time, add much more) it doesn’t really change the performance characteristics of the G90. I’d check out my G90 review for more info about performance.
Would I purchase the G90/GSOC combo if I were in your shoes? Again, it’s early days, so I don’t feel comfortable making a recommendation call yet. The G90 is, without question, a great value at $450 (often even less) investment. I like it primarily as a field radio, though, and once you add the GSOC to the mix, it’s a little less portable because it’s two units with quite a few interconnect cables. Of course, you can swap the GSOC unit for the G90 control head at any time, but that involves attaching and re-attaching the control head each time (there’s no accessible serial port on the back of the G90, for example)
If you’re a huge fan of the G90, the GSOC should eventually be a worthy addition. At present, for your use as a new ham and for SWLing, I’d perhaps consider other options too.
The Icom IC-7300 SDR transceiver
Since you’ve raised your budget to $1,000, I’d consider adding the Icom IC-7300 to your list. At present, via Universal Radio you can buy a new IC-7300 for a net price of $1039.95 after rebates. Sometimes, the price will go even lower although during the C-19 pandemic, I think that’s less likely to happen since supplies are lower than normal for many items.
The IC-7300 has better performance specs than the G90 and can output a full 100 watts if you like. The display is touch sensitive rather than capacitive like the GSOC. The display is also much smaller than that of the GSOC. The IC-7300 has a lower noise floor than the G90.
I think the IC-7300 is a great radio for SWLing, but the audio for broadcasts is sort of “flat.” You might check out this post where we did some audio comparisons. It does have native broadcast recording to an SD card, which I love. The GSOC should be adding this soon, too.
I would include the new Icom IC-705 as a recommendation here, too, but it’s $300 over your budget.
This might be the option I’d take if I were in your shoes.
Get the 20 watt Xiegu G90 ($450) as planned or consider a radio like the 100 watt Yaesu FT-891 ($640), Both of these radios are general coverage and would serve you well for SWLing and ham radio activities. I’d personally invest the bit extra and get the FT-891 since it would also give you 100 watts output and even has advanced features like memory keying.
We actually mentioned both radios in a similar post this year.
If you buy the pricier Yaesu FT-891, you’d still have $360 to invest in your shack!
I’d then buy an Airspy HF+ Discovery ($170–my review here) or SDRplay RSPdx ($200–my review here) and get all of the benefits of a PC-connected SDR.
These SDRs would take your SWLing to the next level. They have uncompromised performance for the price.
Both companies continuously improve their products/applications based on customer feedback. Indeed, check out some of our recent posts about SDR# free upgrades. Mind blowing stuff–!!!
You could even use the SDR as a panadapter for your transceiver which would give you the ability to have a full-screen spectrum display on an external monitor at home.
Of course, these answers only scratch the surface. I haven’t even included used, late model gear in these recommendations.
I’d like to give you a firm recommendation about the GSOC and G90 combo, but I’m waiting to see how this next firmware upgrade goes–early days still.
Post readers: Please comment if you have even more options/suggestions for Tim. What works for you within a $1,000 budget.
Many thanks to SWLing Post contributor, Ivan (NO2CW), who shares the following short demo of the new SDR# Co-Channel interference canceller tool:
That is simply amazing!
Readers note: this powerful tool for DXing is a free upgrade for SDR# users!
Click here to read more about the Co-Channel Canceller.
The following article first appeared in the January 2020 issue of The Spectrum Monitor magazine.
I admit it: I used to be a bit of an old-fashioned radio curmudgeon. One of those, “I like my radios with knobs and buttons” likely followed by, “…and no other way!”
However, about fifteen years ago, many of my DXing friends started turning to the world of software defined radios (or in common parlance, “SDRs”). I staunchly opposed ever following in their footsteps. One of the reasons I for this––a good one––is that, since I spend the bulk of my day in front of a computer, why would I ever want to use a computer when I’m playing radio?
But then…gradually, I found myself playing around with a few SDRs. And I quickly learned that third-generation SDRs were capable of doing something very impressive (and fun), indeed: making spectrum recordings. Using this tool, I found I could record not only the audio of one individual signal, but the audio of entire swathes of radio spectrum. And even more impressive, I learned that you could later load or “play back” the spectrum recording and tune through the bands as if in real time. Any time you want. Before long, I was hooked: SDRs had become my portal into radio time travel!
I quickly found that I loved many of the other advantages of using an SDR, as well, including visual ones––like the ability to view spectrum. The interactive interface allows one to actually see radio signals across the band in real time. I also found incredible value in waterfall displays, which show signals changing in amplitude and frequency over time. Cool stuff.
I purchased my first dedicated SDR in 2012, a WinRadio Excalibur. It was––and still is––a benchmark receiver, performing circles around my tabletop receivers and general coverage transceivers.
And today, although I own and love a number of legacy radios and still listen to them in the good old-fashioned manner to which I became accustomed, I find I’m now spending the bulk of my time DXing with SDRs.
And then, more recently, two amazing things happened in the world of SDRs. Strong market competition, together with serious innovations, have come into play. Thus, for less than $200 US, you can now purchase an SDR that would have easily cost $1,000 US only ten years ago. And now, in many cases, the $200 SDR of today will outperform the $1,000 SDR of yesteryear. We are, indeed, living in good times.
And now––no more a radio curmudgeon––I’m comfortable with my SDR-user status and time at the computer, and glad I was just curious enough about SDRs to let them into my radio (and computer) world.
Since I initially dived into the world of SDRs, I’ve tried to think of a way to take them into the field.
But first, let’s get an obvious question out of the way:
Why would you want to drag an SDR into the field, when a traditional battery-powered radio is so much easier to manage?
After all, you may say, portable and even mobile tabletop receivers require no computer, no hard drive, and are likely more reliable because there are less components to manage or to cause problems for you.
In answer, let’s look at a few scenarios where heading to the field with an SDR system might just make sense. (Hint: Many of these reasons are rooted in the SDR’s ability to record spectrum).
Photo by Henry Be
My good friend, London Shortwave, lives in the middle of London, England. He’s an avid radio enthusiast and DXer, but his apartment is almost a perfect storm of radio interference. Listening from his home is challenging, to say the least: he can only use indoor antennas and RFI/QRM simply inundated his local airwaves.
Many years ago, he discovered that the best way to DX was to go to an area that put urban noise and radio interference at a distance. He found that by visiting large local parks, he could play radio with almost no RFI.
Being a computer guru, he started working on a portable SDR setup so that he could go to a park, set up an antenna, and record radio spectrum while he read a book. His systems evolved with time, each iteration being more compact less conspicuous that the previous. Later, he could head back home, open the recorded spectrum files, and tune through these “time-shifted” recordings in the comfort of his flat. This allowed London Shortwave to maximize the low-RFI listening experience by reliving the time in the park.
Over the years, he tweaked and adapted his setup, often writing his own code to make small tablets and portable computers purpose-built portable-spectrum-capture devices. If you’re curious, you might like to read about the evolution of his systems on his blog.
Clearly, for London Shortwave, an SDR is the right way to capture spectrum and thus likely the best solution for his DX listening.
Typically radio enthusiasts turn to field operation to work in a lower-noise environment and/or where there are no antenna restrictions, often to log new stations and DX.
SDRs afford the DXer top-shelf tools for digging weak signals out of the muck. SDR applications have advanced tools for tweaking AGC settings, synchronous detectors, filters, noise reduction, and even to tailor audio.
The WinRadio Excalibur application even includes a waterfall display which represents the entire HF band (selectable 30 MHz or 50 MHz in width)
On top of that, being able to see a swath of spectrum and waterfall gives one an easier way––a visual way––to pinpoint weak or intermittent signals. This is much harder to do with a legacy radio.
Case in point: I like listening to pirate radio stations on shortwave. With a spectrum display, I can see when a new station may be tuning up on the band so can position the receiver to listen in from the beginning of the broadcast, and never miss a beat.
Or, in another example, the visual aspect of spectrum display means I can easily locate trans-Atlantic DX on the mediumwave bands by looking for carrier peaks on the spectrum display outside the standard North American 10 kHz spacing. The signals are very easy to spot.
Mark Fahey, scanning the bands with his WinRadio Excalibur/Surface Pro 2 combo at our 2015 PARI DXpedition
Whether you’re joining an organized DXpedition or you’re simply enjoying a little vacation DXpedition, SDRs allow you to make the most of your radio time.
Indeed, most of the organized DXpedition these days heavily incorporate the use of SDRs specifically so DXers can record spectrum. Much like example #1 above, doing this allows you to enjoy the noise-free optimal conditions over and over again through spectrum recordings. Most DXpeditioners will have an SDR making recordings while they use another receiver to DX in real time. Later, they take the recording home and dig even more weak signals out of the mix: ones that might have otherwise gone unnoticed.
Earlier this year, Mark gave me this 8TB hard drive chock-full of spectrum recordings.
One of the joys I’ve discovered in making field spectrum recordings is sharing them with fellow DXers. Most of the time when I go to shortwave radio gatherings (like the Winter SWL Fest), I take a couple hard drives to exchange with other SDR enthusiasts. My friend, Mark Fahey, and I have exchanged some of our favorite spectrum recordings this way. I give him a hard drive chock-full of terabytes of recordings, and he reciprocates. Back home (or on the train or airplane) I open one of his recordings and, boom! there I am in his shack in Freeman’s Reach, Australia, tuning through Pacific stations that are not easily heard here in North America, maybe even turning up some gems Mark himself may have overlooked…just as he is doing with my recordings from the southeast US.
I’ve also acquired DXpedition spectrum recordings this way. It’s great fun to “be there” through the recordings and to enjoy some of the benefits of being on the DXpedition in times when I couldn’t actually make it there in person. For a DXer with a consuming job, busy family life, or maybe health problems that limit their travel, an SDR recording is the way to go.
Photo by David Straight
I’m a husband and father, and no matter how much I like to play radio when we’re on vacation, my family comes first, and our family activities take priority.
Having a field-portable SDR setup means that I can arrange a “set it and forget it” spectrum capture device. Before we head out the door for a family visit, tour of the area, or a hike, I simply set my SDR to record spectrum, then listen to what I “caught” after I return, or after I’m home from vacation.
This practice has allowed me to enjoy radio as much as I like, without interrupting our family adventures. Can’t beat it!
With all of these benefits, one might wonder why many other DXers haven’t been using portable SDRs in the field for a while now? That’s a good question.
The WinRadio G31DDC, like many SDRs of the era, has separate data and power ports
In prior years, DXers and listeners might have been reluctant to lug an SDR and its requisite apparatus out with them. After all, it’s only been in the past decade or so that SDRs haven’t required a separate custom power supply; some legacy SDRs either required an odd voltage, or as with my WinRadio Excalibur, have very tight voltage tolerances.
Originally, taking an SDR to the field––especially in places without grid mains power––usually meant you also had to take a pricey pure sine wave inverter as well as a battery with enough capacity to run the SDR for hours on end.
Having spent many months in an off-grid cabin on the east coast of Prince Edward Island, Canada, I can confidently say it’s an ideal spot for DXing: I can erect large wire antennas there, it’s on salt water, and there are literally no locally-generated man-man noises to spoil my fun. Of course, anytime we go to the cottage, I record spectrum, too, as this is truly a honey of a listening spot.
The view from our off-grid cabin on PEI.
The first year I took an SDR to the cabin, I made a newbie mistake: it never dawned on me until I arrived and began to put it to use that my Goal Zero portable battery pack didn’t have a pure sine wave inverter; rather, I found it had a modified sine wave inverter built into it. The inverter could easily power my SDR, sure, but it also injected incredibly strong, unavoidable broadband noise into the mix. It rendered my whole setup absolutely useless. I gave up on the SDR on that trip.
Both the Airspy HF+ (top) and FDM-S2 (bottom) use a USB connection for both data transfer and power. Photo by Guy Atkins.
Today, most SDRs actually derive their power from a computer or laptop through a USB cable, one that doubles as a data and power cable. This effectively eliminates the need for a separate power system and inverter.
Of course, your laptop or tablet will need a means of recharging in the field because the attached SDR will drain its battery a little faster. Nowadays it’s possible to find any number of portable power packs/banks and/or DC battery sources to power laptops or tablets, as long as one is cautious that the system doesn’t inject noise. This still requires a little trial and error, but it’s much easier to remedy than having two separate power sources.
Even a Raspberry Pi 3B has enough horsepower to run SDR applications.
An SDR is nothing without a software application to run it. These applications, of course, require some type of computer.
I the past, SDR applications needed some computing horsepower, not necessarily to run the application itself, but to make spectrum recordings. In addition, they often required extra on-board storage space to make these recordings sufficiently long to be useful. This almost always meant lugging a full-sized laptop to the field, or else investing in a very pricey tablet with a hefty amount of internal storage to take along.
Today we’re fortunate to have a number of more portable computing devices to run SDR applications in the field: not just laptops or tablets, but mobile phones and even mini computers, like the eminently affordable $46 Raspberry Pi. While you still have to be conscious of your device’s computing horsepower, many small devices are amply equipped to do the job.
64-128 GB USB flash/thumb drives are affordable, portable storage options.
If you’re making spectrum and audio recordings in the field, you’ll need to store them somehow. Wideband spectrum recordings can use upwards of 2GB of data per minute or two.
Fortunately, even a 64GB USB flash drive can be purchased for as little as $7-10 US. This makes for quick off-loading of spectrum recordings from a device’s internal memory.
It wasn’t until this year that all of the pieces finally came together for me so that I could enjoy a capable (and affordable!) field-portable SDR setup. Two components, in particular, made my setup a reality overnight; here’s what made the difference.
Last year, AirSpy sent me a sample of their new HF+ Discovery SDR to test and evaluate. To be fully transparent, this was at no cost to me.
I set about putting the HF+ Discovery through its paces. Very soon, I reached a conclusion: the HF+ Discovery is simply one of the best mediumwave and HF SDRs I’ve ever tested. Certainly, it’s the new benchmark for sub-$500 SDRs.
In fact, I was blown away. The diminutive HF+ Discovery even gives some of my other benchmark SDRs a proper run for their money. Performance is DX-grade and uncompromising, sporting impressive dynamic range and superb sensitivity and selectivity. The noise floor is also incredibly low. And I still can’t wrap my mind around the fact that you can purchase this SDR for just $169 US.
The HF+ Discovery compared in size to a DVD
In terms of portability, it’s in a class of its own. It’s tiny and incredibly lightweight. I evaluate and review SDRs all the time, but I’ve never known one that offers this performance in such a tiny package.
Are there any downsides to the HF+ Discovery? The only one I see––and it’s intentional––is that it has a smaller working bandwidth than many other similar SDRs at 768 kHz (although only recently, Airspy announced a firmware update that will increase bandwidth). Keep in mind, however, that the HF+ series SDRs were designed to prevent overload when in the presence of strong local signals. In fairness, that’s a compromise I’ll happily make.
Indeed, the HF+ Discovery maximum bandwidth isn’t a negative in my estimation unless I’m trying to grab the entire mediumwave band, all at once. For shortwave work, it’s fine because it can typically cover an entire broadcast band, allowing me to make useful spectrum recordings.
The HF+ Discovery is so remarkably tiny, that this little SDR, together with a passive loop antenna, can fit in one small travel pouch. Ideal.
My homebrew NCPL antenna
Speaking of antennas, one of the primary reasons I’m evaluating the HF+ Discovery is because it has a very high dynamic range and can take advantage of simple antennas, in the form of passive wideband magnetic loop antennas, to achieve serious DX.
AirSpy president and engineer, Youssef Touil, experimented with several passive loop antenna designs and sizes until he found a few combinations ideally matched with the HF+ Discovery.
My good buddy, Vlado (N3CZ) helped me build such an antenna per Youssef’s specifications. Vlado had a length of Wireman Flexi 4XL that was ideal for this project (thanks, Vlad!). The only tricky part was penetrating the shielding and dielectric core at the bottom of the loop, then tapping into both sides of the center conductor for the balun connections. Being Vlado, he used several lengths of heat shrink tubing to make a nice, clean, snag-free design. I’ll freely admit that, had I constructed this on my own, it wouldn’t have been nearly as elegant!
Youssef also sent me a (then) prototype Youloop passive loop antenna. It’s incredibly compact, made of high quality SMA-fitted coaxial cables. It can be set up in about 30 seconds and coiled to tuck into a jacket pocket. The AirSpy-built loop has a lower loss transformer than the one in the homemade loop, which translates into a lower noise figure for the system.
Click here to read my review of the Youloop.
Let’s face it: SDR kit simply doesn’t get more portable than this.
My Microsoft Surface Go tablet on a hotel bed.
In the past, I used an inexpensive, circa 2013 mini Windows laptop with an internal SSD drive. Everything worked beautifully, save the fact that it was challenging to power in the field and the internal capacity of the hard drive was so small (16GB less the operating system). In addition, it was a few years old, bought used, so the processor speed was quite slow.
This year, on the way back from the Huntsville Hamfest, I stopped by the Unclaimed Baggage Center in Scottsboro, Alabama. This center has a wide variety of used portable electronics at discount prices. I felt pretty lucky when I discovered a like-new condition Microsoft Surface Go tablet and keyboard with original charger for $190. The catch? The only data port on the tablet is a USB-C. But I grabbed a small USB-C to standard USB 3.0 dongle (for $2!) and took a risk that it would work with the HF+ Discovery.
Fortunately, it did! Score!
While the Surface Go is no powerhouse, it’s fast enough to run any of my SDRs and make spectrum recordings up to 2 MHz in width without stuttering. The only noise it seems to inject into the mix is a little RFI when I touch the trackpad on the attached keyboard.
One of my LiFePo batteries
The HF+ Discovery draws power from the Surface Go tablet via the USB port. With no additional power supply, the Surface Go may only power the HF+ Discovery for perhaps an hour at most. Since I like doing fully off-grid operations and needed to avoid RFI from inverters, I needed a portable power solution.
Fortunately, the Surface Go has a dedicated power port, so I immediately ordered a DC power cable with a standard car lighter plug.
At the Huntsville Hamfest I also purchased a small 12V 4.5 Ah Bioenno LiFePo battery and paired it with a compact Powerpole distribution panel kit I purchased in May at the 2019 Dayton Hamvention.
The LiFePo battery is small, lightweight, and can power the tablet /SDR combo for hours on end. Moreover, I have noticed no extra noise injected when the DC power is applied.
My portable SDR kit on a hotel balcony.
Now I have this kit, I couldn’t be more pleased with it. When all of the components of my SDR system are assembled, they work harmoniously. The entire ensemble is also incredibly compact: the loop antennas, SDR, Surface Go tablet, battery, and distribution panel all fit in a very small travel pack, perfect for the grab-and-go DX adventure.
The entire kit: SDR, cables, Youloop antenna, connectors and adapters all fit in my Red Oxx Lil’ Roy pack.
In November, I took the kit to the coast of South Carolina and had a blast doing a little mediumwave DXing from our hotel balcony. We were very fortunate in that I had two excellent spots to hang the homemade loop antenna: on the main balcony, and from the mini balcony off the master bedroom. Both spots yielded excellent results.
What impressed me most was the fact that the SDR# spectrum display and waterfall were absolutely chock-full of signals, and there was very little noise, even in the popular resort area where we were staying. I found that my portable radios struggled with some of the RFI emanating from the hotel, but the HF+ Discovery and passive loop combo did a much better job mitigating noise.
Check out the AM broadcast band on the spectrum display.
But no need to take my word for it. If you would like to experience it first hand, why not download an actual spectrum recording I made using this setup?
All you’ll need to do is:
This particular recording was made on the mediumwave band on November 17, 2019, starting at around 01:55 UTC.
My portable SDR kit capturing spectrum during a hike in Pisgah National Forest.
I’ve also taken this setup to several parks and remote outdoor locations, and truly enjoyed the freedom of taking spectrum recordings back home to dig through the signals.
I finally have a portable SDR system that allows me the flexibility to make spectrum recordings while travelling. The whole setup is compact and can easily be taken in a carry-on bag when flying.
The glory of this is, I can tune through my spectrum recordings in real time and DX when I’m back home, or even on the way back home, in the car, train, or airplane. It’s simply brilliant.
If you don’t already own an SDR, I can highly recommend the AirSpy HF+ Discovery if you’re primarily interested in HF and MW DXing. If you need a wideband SDR, I could also recommend the recently released SDRplay RSPdx, although it’s slightly heavier and larger than the AirSpy.
Thankfully, I am now an SDR enthusiast that can operate in the field, and this radio has had a lot to do with it. I’ll be logging many hours and miles with the AirSpy HF+ Discovery: its incredibly compact footprint, combined with its brilliant performance, is truly a winning combo.
Click here to check out the Airspy HF+ Discovery
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