Many thanks to SWLing Post contributor Don Moore–noted author, traveler, and DXer–who shares the following post:

A Beginner’s Guide to ALE: Part Two

By Don Moore

Don’s traveling DX stories can be found in his book Tales of a Vagabond DXer [SWLing Post affiliate link]. If you’ve already read his book and enjoyed it, do Don a favor and leave a review on Amazon.

In the first part of this series, I explained what the digital ALE mode is and looked at an easy way to get started monitoring ALE stations. In part three, I’ll look in detail at the dozens of countries and hundreds of stations that can be logged in ALE mode. But first, let’s look at a way to let software do the hard work in adding those hundreds of stations.

The Black Cat Approach

Run by longtime DXer Chris Smolinski, Black Cat Systems is a provider of over two dozen quality software programs for radio hobbyists. The one we’re interested in is the Black Cat ALE Vacuum Cleaner. The name describes exactly what it does. The user feeds it a large number of SDR spectrum recordings, and the Vacuum Cleaner sucks up the ALE DX and lists them in a file.

Let’s step through the basics of using the program. But first, you need at least an hour or two of SDR spectrum recordings covering frequencies with lots of ALE traffic. Some of my favorite ranges are 7500-9200 kHz, 10100-11500 kHz, and 15500-16500 kHz.

Here’s the main screen on the Vacuum Cleaner:

I recommend you check both USB and LSB. In the logs reported to the Utility DXers Forum, about 97% of all ALE transmissions are in USB mode. From my experience, if LSB is unchecked, the Vacuum Cleaner will step through the files about twenty percent faster, but you will miss a tiny number of stations.

The kHz settings determine how finely the application will tune in looking for ALE signals. I recommend just checking x.0kHz and x.5kHz. Almost all ALE signals on shortwave are transmitted on frequencies that end in either point-zero or point-five kilohertz. The main exception is the US Department of State, which uses frequencies ending in point-six kilohertz (e.g., 8058.6 kHz). Fortunately, the one-hundred Hertz difference from the point-five kilohertz setting isn’t enough to make a difference except maybe with the weakest of signals.

The next step is the Settings, which are found under the Edit menu. Most values can be left at the defaults.

At the top, the number of decoding threads should be no more than the number of cores that your CPU has. Check the Auto Log box, then enter a destination path to record logs to a file. (Otherwise, the logs that show up in the window will be gone when you close the program.) Next, select the file format of the SDR program used in making the I/Q recordings. Finally, set the file format for your logs. I prefer the single tab format so that I can later import the logs into Excel and sort by frequency.

Now it’s time to decode. Under the File menu, select Open I/Q Files and browse to a folder of spectrum recordings to decode. Click on Open in the file selection box, and the Vacuum Cleaner will start decoding the files. Now take a break and come back in fifteen or twenty minutes. The main screen should look like this.

The current settings and the frequencies being scanned are displayed at the top, under the settings checkboxes. There are actually only 1232 distinct frequencies in that range, but the number is doubled as each one is being checked in both LSB and USB. Below that, the output window lists each file as it is being scanned and ALE logs as they are found. (But be sure you are also recording these to a text file.)

To see a list of files still in the queue, select File > Show I/Q Files Awaiting Processing. After a few files have been processed, this will also show an estimate of how much time is needed to complete the queue. To add additional files to the queue, select File > Pause Processing, add the files, and then select File > Resume Processing. Note that the Vacuum Cleaner processes files in date/time order. If you add files that were recorded earlier, they will go to the front of the queue.

How Long Does This Take?

In the above image, notice that after each file is finished, the time taken to decode it is displayed. These files were all exactly 326 seconds long, and the first one took 262 seconds to decode for a speed of 1.24x actual time. That may not seem important, but it depends on how much you have to decode. In a couple of days of serious DXing with my three Airspy receivers, I can easily accumulate a couple of terabytes of spectrum recordings.

Processing time depends on several factors. The first is the bandwidth/sampling rate. Those files above were recorded with SDR-Console at 768 kHz wide. All other things being equal, a narrower sample will process faster and a larger one more slowly. Depending on the band being monitored, I sometimes record with my Airspys at the 912 kHz bandwidth. Those typically take about 25% longer to decode than 768 kHz files.

Another factor is whether or not the Vacuum Cleaner has to share processing power with other running applications. That slows things down. I mostly decode overnight or at times when I’m not otherwise using the laptop. Under those conditions, my 768 kHz files decode at 1.75x and my 912 kHz ones at 1.45x. But those numbers are for my nearly four-year-old main laptop. An older laptop I have at home tops out at around 1.40x on 768 kHz files with nothing else running. If you have a high-performance gaming laptop, you should get much better numbers than I.

Then there are differences between the various SDR applications in how they store data. I won’t go into the technical details that Chris explained to me, but SDR-Console is more efficient in this regard. In my own testing, I found that files of similar bandwidth and time length recorded with SDR-Console decode at least fifty percent faster than those recorded with the default Elad and Perseus software. I’m satisfied with SDR-Console, so I haven’t tried any other programs. If you have other favorite SDR applications, I suggest doing some comparison tests to see what works best for you.

One application that you shouldn’t use is HDSDR. Chris didn’t have good documentation on the file format for this one and wasn’t fully successful in reverse-engineering it. The Vacuum Cleaner will work with HDSDR, but almost all the callsigns that it finds will be errors. And that brings us to an important question.

How Accurate Is It?

When I started using the Vacuum Cleaner, my main concern was whether it would miss valid signals. There was only one way to find out, so I ran several tests. I would give the Vacuum Cleaner a few hours of I/Q recordings to decode, and then I would process the same recordings manually using Sorcerer, as described in part one. Black Cat not only correctly identified every single ALE transmission that I found with my eyes but went way beyond that. It also found and decoded weak and noise-covered signals that I couldn’t see in the Data Analyzer window but were there when I played them back.

As Chris points out in his documentation, the emphasis on weak signal detection does cause the application to sometimes falsely report bogus callsigns. Some of these are produced by random noise, fooling the system. Others come from poorly received signals. He could have taken a ‘high confidence’ approach and only presented callsigns that had been clearly received. But that would have meant some valid callsigns not being reported. Instead, he went with displaying everything. It’s up to the user to weed those out.

If the decode doesn’t contain any of the keywords (TO, TIS, and TWAS) then it’s probably an error. But poorly received signals can cause partial and incorrect callsigns to be reported with a keyword. Spotting those just takes the knowledge and practice that comes from using the program and ALE reference materials. (That’s the topic of part three.)

Is It Worth the Price?

Black Cat ALE Vacuum Cleaner is a high-quality software available for Windows and macOS, and you can try it before buying. The cost is $99.99.

Is it worth it? If all you want to do is sample what ALE is all about, then probably not. But if you get serious about ALE monitoring and want to add hundreds of ALE stations to your logbook, this is the way to do it. I am 100% satisfied with the Black Cat ALE Vacuum Cleaner. I’ve decoded several thousand hours of I/Q files with it over the past few years. (When running multiple SDRs at a DXpedition, it’s easy to accumulate seventy or eighty hours per day.) The program also has a few other tricks I haven’t covered. For example, it is possible to actively monitor a folder and decode I/Q recordings as they are created.

In part three of this series, I’m going to take an in-depth look at the countries and stations that can be logged in ALE mode. Once you’ve seen how much DX there is to log, you might just be convinced, like me, that the program is worth the price. And you married guys can tell the wife that you’re buying a new vacuum cleaner that only you will use, hi!

The Vacuum Cleaner isn’t the only program that Chris has for ALE monitoring. Black Cat ALE is a different program that does live monitoring of up to twenty-four ALE frequencies simultaneously with SDR-Console, assuming your laptop has the resources to handle that.

Finally, Chris tells me that he’s been experimenting with using the Vacuum Cleaner with wide-bandwidth I/Q recordings on high-end laptops. On his M4 Max MacBook Pro, he’s able to process 32-MHz wide recordings at about 0.50X real time and 16-MHz wide recordings at about 0.97X real time. As he says, it won’t be long until it will be possible with the right equipment to monitor the entire HF spectrum for ALE signals in real time. And that will be fun!

Links

• Black Cat Systems main page: https://blackcatsystems.com/
• The ALE Vacuum Cleaner: https://blackcatsystems.com/software/black_cat_ale_vacuum_cleaner.html

Many thanks to SWLing Post contributor Don Moore–noted author, traveler, and DXer–who shares the following post:

A Beginner’s Guide to ALE: Part One

By Don Moore

Don’s traveling DX stories can be found in his book Tales of a Vagabond DXer [SWLing Post affiliate link]. If you’ve already read his book and enjoyed it, do Don a favor and leave a review on Amazon.

To me, part of the excitement of DXing has always been logging new stations. From the very beginning (over fifty years ago), I went after shortwave broadcast (SWBC), medium wave, and voice utility DX. Up until the mid-90s, I usually averaged logging one new SWBC station per week. Today, it’s hard to add more than one or two each year. There are also far fewer voice utility stations on the air today. At least medium wave is still going strong. Several years ago, my quest for logging new stations on the shortwave frequencies got me involved in DXing digital utility stations. I wrote an article here on monitoring DSC stations: https://swling.com/blog/2022/11/guest-post-monitoring-digital-selective-calling-dcs-with-yadd/).

But DSC is just one of several digital modes that I’ve been playing around with. The one that I’ve found most interesting – and the one that has yielded hundreds of new stations in numerous countries – is ALE.

Now, I am not an expert at monitoring ALE. I’m just an advanced beginner. But I think I know enough to help other beginners get started. And if you are an ALE expert reading this, I welcome your additions, corrections, and even criticisms to the comments section. I still have a lot to learn, too.

What is ALE?

Ever since the early days of radio, one of the most important uses of the shortwave spectrum has been two-way communication. It provides a means for an organization’s far-flung offices or bases to communicate without relying on external infrastructure. That remains true even today because satellites can malfunction and evil powers can cut undersea cables.

But shortwave isn’t consistent. The frequencies that work best between any two points will vary by time of day, time of year, solar conditions, and a host of other factors. In the old days, radio operators had to understand radio propagation to make an educated guess as to the best frequency to use to reach a particular distant station. Sometimes they guessed wrong, and stations would struggle to communicate or maybe not even connect. ALE, or Automatic Link Establishment, was designed to make two-way shortwave communication as simple as making a telephone call. Depending on your point of view, it has taken the guesswork out of frequency selection … or made it so easy that any dummy can be a radio operator.

In an ALE system, each station is assigned a unique identifier and the network has a set of preconfigured frequencies spaced throughout the shortwave spectrum. For example, here’s a partial list of frequencies and stations for the United States Air Force, one of the most active ALE networks.

USAF Common Frequencies: 4721, 5684, 5702, 6715, 6721, 8968, 9025, 11181, 11226, 13215, 15043, 17976, 18003, 23337, 27870 kHz

Most Active USAF Stations

• ADW Andrews Air Force Base, Maryland, USA
• AED Elmendorf Air Force Base, Alaska
• CRO Croughton Air Base, United Kingdom
• GUA US Air Force Base, Guam
• HAW Hawthorn Air Force Base, Ascencion Island
• HIK Hickman Air Force Base, Hawaii
• ICZ US Air Force Base, Sigonella, Sicily, Italy
• JDG US Air Force Base, Diego Garcia Island
• JNR US Air Force Base, Salinas, Puerto Rico
• JTY US Air Force Base, Tokyo, Japan
• MCC Beale Air Force Base, California, USA
• OFF Offutt Air Force Base, Nebraska, USA
• PLA Lajes Field, Azores

The key to the system is a piece of software called the ALE controller. At periodic intervals, the ALE controller at a particular station, say PLA, will loop through the frequencies and send a “sounding” out on each one. That’s just a short digital identification burst saying “This is PLA!” Here’s a recording of an ALE sounding.

That’s not the kind of signal that anyone would enjoy listening to all day. Fortunately, no human being has to do that. Instead, all the other controllers in the network are monitoring every frequency and automatically make note of how well PLA is received (or not) on each channel. Now, if someone at Offutt Air Force Base needs to send a message to Lajes, they just go to their ALE controller and enter “PLA.” The system will select the best frequency to use based on the most recent observations. That’s the basic explanation. If you want to understand more, see the links at the bottom.

Monitoring ALE

You can’t DX ALE with your ears. A computer program has to do it for you. There are several hobby programs that do the job, and I’m going to look at two of them. The first one will get you started, and the second one will take your ALE DXing to the top.

I began with Sorcerer, a free program that decodes several dozen digital modes. See the links below for downloading. The program doesn’t need to be installed. Just unzip the file and place the executable in a suitable location. Next, you need an SDR and an SDR application. I prefer SDR-Console for digital work, but any SDR program will work if you can feed the audio into a virtual audio cable. And that’s the other thing you need – a direct audio connection from the audio output of your SDR application to Sorcerer. There are several similar products available, but I recommend VB-Cable. Your first VB-Cable is free, and you only need one to run Sorcerer. If you want to expand, you can buy more VB-Cables later.

Here’s the main window that opens when you start Sorcerer.

The first time you use Sorcerer you will need to connect it to your VB-Cable. On the menu select File then Options. Find the cable under the Soundcard list and save.

Open your SDR application and tune it to 11181 kHz. Set to USB mode with a filter value of around 2.8 kHz. That is one of the most heavily used frequencies by US Air Force bases around the world. Wherever you are, something should be received. Next, set the audio output of your SDR application to go to VB-Cable. In SDR-Console that’s done by a drop-down box under the current frequency. Next, slide the volume level all the way up.

Now go back to Sorcerer and confirm you are getting audio from the SDR application.

Now select Add Decoder from the top menu in Sorcerer. Then select SELCALL on the left side and scroll down and double-click to select MID-STD 188-141A ALE from the options.

That will open a large decoder window, which you can resize as needed.

Now, go get a cup of coffee and come back in about thirty minutes.

Sample Sorcerer Output

Let’s take a look at some sample output from Sorcerer. These loggings were made on 7915 kHz, a frequency used by the Carabineros (National Police) in Chile. First, Sorcerer shows the time and date the decoding was done per the current time on the laptop. If you are monitoring live, those are the correct date and time of the reception.  For the record, I was decoding from SDR spectrum recordings in these examples, so the times and dates are not the real ones. (I got the real ones from the spectrum recordings.) TWS stands for “This Was” and EOM for “End Of Message.” ILLAPEL and TALTAL are the station identifications, which in this case correspond to two Chilean cities. Note that sometimes the end of the ID can be cut off if reception isn’t clear.

These next loggings are from the national police of Colombia on 7560 kHz. Villavicencio is a city east of the Andes, and Sumapaz is a national park in the remote mountains south of Bogotá.

Here is a string of loggings on 7527 kHz, a frequency used by the US Coast Guard and other US government agencies. But here we have a TO, which means someone is trying to call X09. That happens to be a C-27J Spartan, a medium-range surveillance aircraft used by the US Coast Guard. Who’s doing the calling shows up in the final line. TIS (“This Is”) is a variation on TWS. LNT is the identification for CAMSLANT, the big US Coast Guard station in Portsmouth, Virginia.

The Limits of Single Frequency Monitoring

DXing live and monitoring one highly active frequency at a time with Sorcerer makes for a good introduction to ALE. However, if you just stick to monitoring easy frequencies like the USAF ones, you’ll get a lot of logs, but it won’t take long until you feel as if you’ve gotten everything. There are hundreds more ALE frequencies out there, such as the Chilean and Colombian police ones. But those are less active and might only be received at your location when conditions are just right. If you go after those by live monitoring with your SDR parked on a single frequency, you’ll spend a lot of days without getting a single hit.

What is needed is a way to cast a wide net to catch all the activity in a particular band. The idea I came up with was to use the Spectrum Analyzer feature of the SDR-Console program. See my article on this highly useful feature for an understanding of how this works.

Using an Airspy HF+ Discovery, I would make several hours of spectrum recordings and then use the Spectrum Analyzer to visually find the ALE signals. Here’s a string of three long ALE bursts on 7953 kHz and a single weaker one on 7991 kHz. (Some other digital modes look the same on screen.)

I just had to click on a signal to play it into Sorcerer to get the ID. The process worked really well, and I found a lot of stations this way. But it was also tedious and time-consuming. I wanted something better … something that did the hard work for me. That’s what technology is for, right?

Stay tuned for Part Two … 

Links

• Sorcerer Download. Be sure to only download from this link and not from one of the many public download sites. Some years ago there were instances of Sorcerer infected with malware on public sites: https://www.kd0cq.com/2013/07/sorcerer-decoder-download/
• VB Cable Download. Note, it is also possible to use Sorcerer by feeding the audio output from a traditional receiver into the audio input of a laptop. https://vb-audio.com/Cable/
• Wiki Article on ALE: https://en.wikipedia.org/wiki/Automatic_link_establishment