Finding Rare DX with the Data File Analyzer
By Don Moore
Don’s DX traveling stories can be found in his book Tales of a Vagabond DXer.
I’ve been a real jack-of-all-trades in my over five decades of DXing. I began with SWBC (shortwave broadcast) but soon branched out to medium wave and voice utility. Later I added longwave beacons and more recently I’ve gotten into digital utility stations. My goal has always been to log lots of different stations from lots of different places. And the rarer they are, the better.
For SWBC and medium wave stations, as well as scheduled utility broadcasts such as marine and aeronautical weather reports, the DXing process is simple. You tune to a frequency at a time when a station is scheduled to be on the air. It’s either there or it’s not there. If it’s not there then maybe propagation isn’t right or maybe your antenna/receiver setup isn’t the best for that frequency band or the station’s power level. You tune away to find something else with plans to try again another day.
But it’s not always that easy. Most utility stations do not have fixed schedules and only come on as needed. The best example of that is two-way marine, aeronautical, and military voice communications.
In eastern North America, tune to 8906 kHz anytime from late afternoon until morning and set your receiver to USB mode. You’ll probably hear empty static at first but it’s unlikely that more than ten or fifteen minutes will pass before you’ve heard some aeronautical traffic. The frequency is assigned for communication on the North Atlantic and is heavily used by aircraft communicating with New York Radio, Gander Radio (Newfoundland, Canada), and Shanwick Radio (Shannon, Ireland). If you keep listening, the frequency will probably be occupied around 25% of the time. Wherever you are in the world, there are a few heavily used air frequencies like 8906 kHz and listening to them can be fascinating. But I want to log more than just a few easily heard stations.
Sticking to aeronautical DX, there are many assigned frequencies for different regions and air routes around the world. But propagation to those distant areas is unpredictable and less-used routes have fewer flights. Fewer flights mean less radio communication and more empty static. The most interesting frequencies may only see traffic a few times a week.
Hearing the rarest voice utility DX requires listening to lots of empty static just to get a brief DX catch. For years my process was simple. I would set my receiver to an interesting frequency and leave the tape recorder running while I sat nearby listening and doing something productive. I got some very good DX over the years that way. But I don’t want to think about how many long hours of empty static I listened to in order to get that DX.
SDRs offered some improvement. Instead of audibly monitoring a specific frequency I could now make a spectrum recording that included a band of interest, say the 8815 to 9040 aeronautical band. During playback I could visually monitor the SDR waterfall for interesting signals. That works. But watching an SDR waterfall scroll by for three or four hours gets tedious quickly.
(When I refer to SDRs, I mean ones consisting of a small box that is connected to and controlled from a computer using a software program. None of this applies to models such as the Malachite line or the Icom IC-R8600, which use SDR technology inside but mostly function as a traditional receiver.)
Finding a Better Way
That better way is, I think, one of the most exciting DX tools out there – the Data File Analyzer in the SDR-Console program. Since I learned about it a few years ago, the Analyzer has gotten me all kinds of catches that I probably wouldn’t have gotten otherwise. Let’s start with an overview and then dig into the how-to.
SDR-Console is one of the better-known SDR programs and it works well with most of the common SDR radios on the market, including the Airspy, Elad, Perseus, and SDR-Play models. Here’s what the main window looks like:
The Data File Analyzer is a second window that produces a scrollable waterfall display for the entire length of an SDR spectrum recording. The display is similar to a standard waterfall with frequencies along the bottom and times along the side. However, there is also a scroll bar on the right side for browsing through the entire length of the recording. Instead of watching a four-hour spectrum recording slowly roll by in real time, I can scroll through the window looking for DX.
And this is what makes the Data Analyzer really useful. When I spot an interesting signal, I click on it and that causes the main window to start playing at that time and frequency. Now going through a four-hour spectrum recording takes from a few minutes to around half an hour, depending on how much DX I find.
Here’s a closeup of part of that same screen of spectrum recording made on 24 October 2024 at a DXpedition in western Pennsylvania, USA.
“A” marks a short exchange between an aircraft and Ndjamena Radio in Chad on 8894 kHz. “B” is Niamey Radio in Niger on 8903 kHz. “C” is Gander Radio on 8891 kHz. Just to the left of that is a string of digital signals. “D” is New York Radio on 8918 kHz. Again, there is a string of digital signals just to the left. Finally, “E” is communication from Dakar Radio in Senegal and Sal Radio in the Cape Verde Islands on 8861 kHz. I caught four African aero stations in just four-and-a-half minutes. I could also show you long stretches of time when there was nothing interesting coming in. With the Data File Analyzer I was able to visually find and focus on the DX and not waste my time with the empty static.
Here’s another image taken at the same DXpedition. Notice the three transmissions between 8820 to 8845 that seem to be mirroring one other.
That turned out to be Flightwatch Brisbane, the Australian regional aeronautical network. It uses multiple transmitter sites on 8822, 8831, and 8843 kHz to cover the entire country. I had never logged it before and I doubt I would have found it if DXing in the traditional manner.
The How-To
Here I’m going to assume that you already have SDR-Console installed and know the basics of how to use it, including making spectrum recordings. (If not, see the links at the end.) This article was written using version 3.4 of SDR-Console. Some of the functionalities described are not in earlier versions, so upgrade if you are not up to date. And I should point out that while you can do this on a single monitor, it works more smoothly if you have a dual monitor setup and can put each window on a different screen.
The Data File Analyzer doesn’t appear in the menu by default, so the first step is to add it. Open SDR-Console. Select “View” on the top menu bar. On the right side, click on the three dots labeled “Select” to open the program options box. Enable the Analyzer, click OK, and wait for the program to restart.
After SDR-Console restarts select the “View” menu again. You should see the Data File Analyzer option on the far right.
Now we need some files to analyze. To start, I recommend recording a narrow spectrum, such as 384 kHz wide. Most SDRs offer that as an option. Pick a band and time where you can expect to find some signals. For marine communications, 8200 kHz is a good center frequency or use 8900 kHz for aeronautical stations. In most parts of the world those ranges should have some action from late afternoon until the next morning. With SDR-Console you can either record to one large file or a series of 1 GB files. I prefer using the 16-bit 1 GB option as I think really large files slow down the Data Analyzer. Record for at least an hour or two.
Running the Analyzer
When your recording is finished, open the Analyzer window. In the top left corner, click on “New” to open the file selection window and browse to select the file. Clicking the Play button will open the Options window. For now do not select Enable in the Center box and under Update Rate select 4 lines per second. We’ll discuss these settings below.
Click OK. Give the Analyzer a few minutes to run. The total size of the files and your computer’s speed and memory will determine how quickly the Analyzer works through a set of files. I wouldn’t recommend running it in the background while streaming an HD video. But doing routine tasks like checking e-mail or browsing the web shouldn’t cause a problem.
Once the Analyzer has finished you can click Save in the top menu bar and save the analyzed data to an XML file. That’s only necessary if you expect to close the Analyzer and come back to the file later. If you do save XML files be sure to periodically delete the ones you no longer need as they can be very large.
Let’s check out some of the items on the menu bar across the top of the Analyzer window. First, your waterfall may not be as easy to read as my examples above. Click on the Contrast option on the menu bar to bring up the Contrast Slider control and make any necessary adjustments. Click on the Contrast option again to close the slider. Just below the Contrast option is a button for UTC. Select that to have times displayed in UTC instead of whatever local time zone your laptop is set to. Further to the right is the start button. Click on that to start playback in the main SDR-Console window. Just to the right of that is the Snap setting which determines the frequency precision when you click on a signal. I find 1 kHz to be best. Finally, in the center of the menu-bar, turn on the Crosshairs option.
You’re now ready to DX. Start at the bottom of the display, where the time begins, and work your way up. When you find an interesting signal, hover the mouse cursor over it to show the time and frequency and click on it to open the main window at that time and frequency. In this example, the frequency is obviously the aeronautical frequency of 11279 kHz. I just need the crosshairs display to show something within +/- 500 Hz and the Snap setting will round it to 11279.0 when the signal opens in the main window.
Hopefully the first time you use the Data File Analyzer you’ll be overwhelmed with all the information in front of you. That’s good – you have a lot of signals in your recording. Over time you will learn what’s routine and what’s unusual and also how to visually distinguish between voice and digital signals. Then you can focus on what is interesting to you.
Now let’s move on to some finer points of using the Analyzer.
Dealing With Spectrum Width
So now you have a 384 kHz wide spectrum display in your Analyzer window. If you have a large monitor that looks great. But if you’re looking at a 13-inch laptop display you might be feeling a little eyestrain. One of the disadvantages of the Analyzer is that it displays the entire width of the analysis and there is no way to zoom in. The only way around that is to run the analysis on a narrow range of frequencies instead of on the entire spectrum width.
To understand what I mean, check the following graphic. The images are equally sized screenshots taken on my 15.6-inch Arzopa travel monitor. In the top I ran an analysis of the entire width of a 1536 kHz wide recording made with my Elad FDM-S2. At the bottom I ran an analysis of a 250 kHz wide portion centered on 8230 kHz for the marine voice band in the same files. Not only is it easier to distinguish the individual signals on the bottom, but some weaker signals below aren’t even visible at the top. Of course, to DX the rest of the recorded spectrum I would have to run further analysis at the narrower width.
To control the analysis width, we need to go back to the Settings window when running the original analysis. Click Enable in the Center box, enter a frequency within the limits of the file, and then select a bandwidth.
The program will warn you if you input a center frequency that would extend the analysis outside the limits of the file.
Which analysis width works best for you will depend on the size and resolution of your monitor and how good your eyesight is. When I had a 21-inch monitor I could go up to 400 kHz before I started having trouble seeing weaker signals. On my smaller Arzopa travel monitor, 300 kHz wide seems to be the top. With recordings made at wider bandwidths you just have to run multiple analyses. To analyze a 768 kHz wide file on the Arzopa I make two runs at 250 kHz wide and one at 300 kHz wide, with a little bit of overlap.
Lines Per Second
The other option in the analysis settings window that affects readability is Line Per Second. In the above image I used a setting of four. The next picture shows the difference between four lines per second on the left and one line per second on the right. The right side shows about thirteen minutes versus only three-and-a-half minutes on the left. However, some voice utility messages are very short. A five-second message using twenty lines on the left side would be much easier to spot than if using just five lines on the right.
Bill Nollman points out another thing to consider with Lines/Second. Look back a few images to the General Settings window where I set the Update Rate to 4 Lines/Second. Just below that it shows that this will produce 43,204 total lines. Bill says that, in the current release, if this value is over 60,000 then the time display on the analyzer will show gaps. His workaround is to use the Start and Finish Time option at the top of General Settings to analyze the files in timed sections not exceeding 60,000 total lines. Just be aware that when using the workaround the first timed section works as expected but the next may not work correctly for point and click tuning.
File Selection Window
The first step in running the Analyzer is to click New to open the file selection window. That window shows a lot of useful information and you can reorder the columns, as I have, to better see that. This next image shows mostly MW files I recorded in Rafina, Greece. First there is the start date/time, then file name (or name of the first file in the chain), and next the total duration of the spectrum recording. After that there is the center frequency, bandwidth, and the total file size and number of files in the spectrum recording. Under Format here, I have both files made in SDR-Console and made in the Winrad format with HDSDR. I’ve also used Elad files in the Analyzer and I believe it works with most standard SDR file formats.
The 00 File
Depending on the SDR program used, long spectrum recordings produce a chain of files designated file_00, file_01, file_02, etc. When the file selection window is open, the Analyzer lists only the initial file_00 files. And that’s fine as you likely want to analyze the entire chain. However, if you accidentally delete the initial file (as I once did) then each subsequent file is listed individually and the Analyzer won’t analyze the entire chain in one single go. The work around is to rename the file_01 file to file_00. That’s it. The Analyzer doesn’t care that there isn’t a file_01 file. But it has to see that file_00 file to analyze an entire chain of files.
This missing initial file problem may only be an issue with recordings made using SDR-Console. Brett Saylor had no such problem when testing using Perseus recordings made with the native Perseus program nor with Mestor. I suggest testing this out with whatever recording program you use. Or better yet, don’t accidentally delete that initial file!
Using the Analyzer
As with any new software, it takes some time to learn how to best use the Analyzer. My method is to start at the beginning (bottom) and work my way up. If I find an interesting signal but can’t identify it I follow the frequency further up the spectrum to see if the station comes back later when conditions may have improved. How long does it take me to go through a three-hour set of files 250 kHz wide? It depends on how many interesting signals there are. Three or four minutes will do it if reception was poor. I’d say twenty minutes is normal. Even the best ones don’t take more than thirty to forty minutes. Voice utility transmissions are typically short.
While I primarily use this for utility DXing, I’ve also found some uses for medium wave DX. I’ll explain those later in another article.
So if you want to hear some serious voice utility DX – and you don’t want to spend hours listening to empty static to get it – give the Data Analyzer a try. You won’t be disappointed.
Thank you to Ralph Brandi, Bill Nollman, and Brett Saylor for reviewing this article and making useful suggestions.
Links
- Top page at SDR-Console. Help files can be found under the Console heading on the top menu: https://www.sdr-radio.com/
- Download page for SDR-Console: https://www.sdr-radio.com/console
- SDR-Console Quick Start Guide: https://www.sdrplay.com/docs/SDR-Console-SDRPlay-RSP_QuickGuideTips.pdf
- More SDR-Console tips: https://swling.com/blog/2018/02/sdr-console-version-3-a-holy-grail-sdr-application-for-the-radio-archivist/
- Video on using the Data Analyzer for FM DX: https://www.youtube.com/watch?v=g0meKEchPFA
Thank you, Don. Most excellent tutorial! I’ve put the Data Analyzer on my list of things to explore.
This is an awesome article. Do you mind if I share it with my YouTube (hamrad88) subscribers?
Thank you,
Tom Stiles
The “live” website for HF aircraft frequencies in most parts of the world is:
https://radio.arinc.net/atlantic/
https://radio.arinc.net/pacific/
The Pacific listing seems for reliable.
Excellent tutorial, thank you so much!
An outstanding tutorial, Don. Thank you for sharing this brilliant technique for digging out our more ephemeral forms of DX! Your excellent explanation of the Data File Analyzer tool in SDR-Console is not only insightful but also incredibly practical for anyone looking to uncover signals that might otherwise go unnoticed.
I only wish tools like this were available when I was a budding DXer in the late 70s and 80s. I can only imagine how chock-full that spectrum would have been with signals back then!
Thank you again, Don!
I agree.
Wonderful job, Don!
I will save this for future reference.
Cheers, Jock