sdrRewind and Black Cat ALE

Many DXers record large swaths of the radio spectrum, and then go back to analyze the recordings, looking for signals of interest. Much of the time, they play the recordings back through their SDR software. This works, but is a slow process, no better than monitoring in real time.

Modern software can dramatically speed up the process. In this article, I’ll show how sdrRewind and Black Cat ALE can team up and speed up the process of finding and decoding ALE (Automatic Link Establishment) transmissions.

Black Cat ALE is a full featured multi-channel ALE decoder for Windows and macOS. It decodes ALE transmissions from either audio fed into a sound card input (live decoding) or from WAVE audio files. Download a copy here:

sdrRewind may take a little more explanation. Rather than just play back an SDR recording file, it allows you to select any of your SDR I/Q recording files, and display a waterfall of the entire file at once, as one large waterfall, with a temporal resolution of one second per line. This is more than adequate to see the various transmissions contained in the recording. Select a signal of interest by dragging a rectangle around it with your mouse, and sdrRewind will demodulate and play back the audio, either to your speakers or a virtual audio device feeding a decoder. It can also demodulate to WAVE files, which can then be fed into your decoding software.

It’s also possible to define a set of frequencies and process several SDR I/Q files at once, generating a collection of WAVE files which can then be fed into the decoding software. In the case of Black Cat ALE, it can be configured to monitor a directory looking for new WAVE files, and automatically process them. So even if the demodulation and decoding process will take some time, you can set it up, then walk away and do something more productive while your computer is busy processing the data. Then come back when it is done and view the results.

Download a copy of sdrRewind here:

Black Cat ALE Configuration:

Select Set Directory To Monitor For New Files from the File menu, and choose the directory in which sdrRewind will store demodulated WAVE files. (Create one if you need to)

Select Monitor File Directory from the File menu. Black Cat ALE will start looking in this directory for new WAVE files. The name of these files must end in “.wav” or “.WAV”. It will ignore any files that already exist in this directory.

sdrRewind Configuration:

Set the directory for your SDR recording files, using Set Recording Directory in the File menu

Open Settings in the Edit menu, go to the Demod Directories tab, and create one or more entries for where demodulated WAVE files should be stored, including at least the directory Black Cat ALE will be monitoring. Create each entry by right clicking on the list and select Add Entry. Then right click on that entry and select Set Path and select the directory to use. Repeat as necessary. Close Settings. Go to Select Demod File Directory in the File menu and select the directory where Black Cat ALE will be monitoring for new WAVE files.

Select one of your SDR I/Q recording files from the list of files in the list on the left side of the main window. After a moment, a waterfall for the entire file will appear. Adjust the min and max dB sliders as necessary for good contrast.

Set the mode to USB.

Find an ALE signal in the waterfall and drag around it with the mouse cursor (can’t find any? Go to another I/Q file). You’ll want to make sure the lower frequency is an integer kHz value (or 0.5 kHz for those ALE channels), so edit the frequency as needed. Zero Frequency kHz in the Edit menu can quickly do this for you. Don’t forget to make sure the upper frequency is high enough to cover the entire ALE spectrum, about 3 kHz. Click the Timestamped button. sdrRewind will demodulate the signal and write it to the specified directory. When Black Cat ALE sees the file, it will open and decode it, printing out the results.

Sometimes you want to decode ALE signals from one or more specific frequencies, over an entire set of SDR I/Q recording files. sdrRewind can help with this as well.

Select Demodulate Multiple Files from the Edit menu and a new window appears.

On the left hand side is a list of your recording files, as in the main window. Select a file and basic information about that file will be displayed: the center frequency, sample rate, bandwidth, starting date and time, and length in seconds.

Demodulation settings are displayed immediately to the right of this, again as in the main window. Configure this for the frequency of interest, then select one or more I/Q files and click the Start button. Each I/Q file will be demodulated and written to a separate timestamped WAVE audio file. The entire I/Q file will be demodulated, from start to finish.

Do not make any changes to any controls in this window will files are being processed.

If you wish to demodulate several frequencies from each file, instead use the list to the right:

Right click in it and select Add Entry. A new row will be added. Set the low and high frequency limits of the IF passband, as well as (optionally) the pass band tuning (PBT). Change the mode by right clicking on it, and select a different mode from the popup menu. The same AGC settings will be used for all entries.

When you are finished, click the Start All button. Each I/Q file will again be processed, this time for each of the frequencies in the list. Click abort to stop processing additional files, however the file currently being processed will need to finish.

The Clear button can be used to quickly remove all entries from the list.

KitchenAid Mixer QRM

I discovered a new QRM / RFI source today, my wife’s new KitchenAid 7-Quart Pro Line Stand Mixer. Here’s a waterfall screenshot after it turned on, you can see the roughly 15 kHz spaced bands of interference. These use a DC motor, presumably that is the cause of the RFI, vs mixers with a regular AC motor.

Fortunately she doesn’t use it that often, and she’s testing out a new low carb dough recipe, so I can live with it. Speaking of low carb, here’s our low carb pizza recipe.

A Christmas card from… the Voice of the Islamic Republic of Iran

The other day a large envelope from the Voice of the Islamic Republic of Iran arrived in the mail, the kind of envelopes they put QSL cards in. I had sent a report a few months ago, but already received that QSL card.

I opened it, and instead of a QSL card… there was a Christmas card:

The Squid – A Universal Matching Transformer for Beverage, Longwire, Dipole, Random wire, K9AY, Flag, EWE… and More Antennas

I built my own “universal” matching transformer for connecting dipoles, beverages, loop antennas, etc. to coax cable, rather than having to wind several transformers and test each to see which impedance ratio provided the best match. After some interest from others who wanted one, they’re now available for purchase.

Each contains a tapped transformer, providing many winding ratios, matching a range of impedances. Each tap on the transformer comes out via a color coded wire, making it easy to determine which pair to use. You can also just go through the various combinations, to find best pair to use. The output is a standard SO-239 socket, which you can directly plug coax with a PL-259 connector into. Or you can use an adapter if you have different coax, I tend to use RG-6. That’s a 75 ohm cable, but it’s fine to use here because I can still select a tap that matches the impedance.

For a dipole antenna, one wire goes to each leg of the dipole. For a loop, connect to the two wire ends. For a beverage, one wire to the antenna, the other to the ground rod. And so on. Note that the transformer is only designed for receiving applications, not transmitting.

The transformer has three isolated eyebolts. Two are used for the antenna connections to take the strain off the tap wires (don’t just directly connect to them) and the third to hang the transformer.

Unused taps should be covered with electrical tape, so the wire does not corrode.

More details as well as ordering information on The Squid page.

DX ToolBox 5.0.0 Beta for Windows and macOS

I’ve released another beta version of DX ToolBox 5.0.0 for Windows and macOS. I’m continuing to work on SWBC related features. This update adds search features to the Logbook which is new to version 5, and some more tweaks to the Reminders window.

Some notes on what I’ve been adding to these beta versions:

The Logbook works just like a traditional logbook, where you can log reception of stations with all the pertinent details (station, time, date, frequency, signal, country, program details, QSL sent/received, etc). The logs can be searched, making it easy to find particular entries. You can even get lists of which stations you’ve send reports to, and are still waiting for QSLs back, so you know when to send followup reports.

The Logbook is tightly integrated with the SWBC schedules window. Say you’re tuned into a frequency, and use the SWBC schedules window to identify the possible broadcasts it could be. Once you’ve decided on the station, you can right click on that entry from the schedules window, and a new log for the transmission is created with many of the fields already filled in for you. Just add/edit whatever additional information you wish, and log the broadcast.

You can right click on entries in your logbook, and automatically search the current schedules for other transmissions by this station, on this frequency, or from this country. You can also do this from entries in the schedule window. Say you find a station or transmission of interest, but can’t hear them right now. By right clicking, you can bring up a list of other transmissions or frequencies used by that station, so you can try them. Or you can get a list of other stations on the same frequency, to see what other stations could be on right now, making it easier to guess what you might be hearing.

One of the most powerful new SWBC related features of the DX ToolBox betas is the Reminders window. When you find transmissions you want to tune in to later, just right click on them to add them to the reminders window. This window is sorted chronologically, and continuously updated every minute. You can glance at it to see what broadcasts of interest to you are on now, or coming up. And the same right click options are available to log transmissions, or look for other transmissions on the same frequency, by the same station, etc. This is a great way to keep track of what you want to listen to, and not forget about them until it’s too late and they’ve signed off. You can also get a OS notification from DX ToolBox that a reminded broadcast is coming up, even if it is in the background.

If you want to give DX ToolBox a try, you can download the beta versions here, scroll down to the bottom of this page: