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A full featured program that decodes and displays Global Maritime Distress and Safety System (GMDSS) / Digital selective calling (DSC) transmissions, available for macOS and Windows.

Tune your HF / shortwave radio or SDR to a GMDSS/DSC frequency and feed the audio into your computer's sound card input, and start receiving and displaying GMDSS/DSC transmissions in minutes.

Works great with SDR software and virtual audio cables! Run up to 8 GMDSS decoders in parallel at the same time, each tuned to a different frequency.

You can change the color scheme and font type/size to your preferences.

Black Cat GMDSS is available for download and trial prior to purchase, so you can make sure it works correctly with your setup. It's available for Windows 8, 10, and 11 (Windows 7 is not supported) as well as macOS.

Nils Schiffhauer (DK8OK) has a review with usage tips that may be helpful.

Nils has also written a guide for setting up SDR Console for multi channel reception.

Paolo Romani IZ1MLL has also written a guide to using Black Cat GMDSS with detailed information about setup and use.

The main window displays recently received messages along with a convenient and thoughtfully arranged user interface (click on any image below for a full sized version) with decodes from each frequency both separately shown as well as combined into one view:

Messages from coastal stations are also separately broken out into their own display, with a concise and easy to read single line format"

Another window displays a table summary of all received transmissions from coastal stations, on a per frequency and total basis. This information is stored on disk and retained from run to run:

Coastal stations with messages are also displayed on a map, which can be panned and zoomed as desired, along with the total number of messages from each station:

There's also a database of all received messages, which can be searched and sorted based on all the possible parameters:

Buy Your Copy of Black Cat GMDSS Today

Start decoding GMDSS transmissions in just minutes!

$29.99 Registration code sent by email, software download

Black Cat GMDSS is only $29.99 (Introductory pricing). Purchase also entitles you to all updates and new versions released over the next full year, free of charge, which of course you can continue to use forever.

Free To Try!

Not sure you're ready to buy Black Cat GMDSS? You can download a fully featured copy to try out, before you buy it.


Black Cat GMDSS 1.0.0 for Windows - Windows 8, 10, 11 - 27 November 2022

Black Cat GMDSS 1.0.0 for Mac OS X - Mac OS X 10.10 and later, 64 bit - 27 November 2022

A virtual audio cable/driver is required for use with SDR programs. We have a list of third party programs here.

GMDSS Frequencies: 2187.5 kHz, 4207.5 kHz, 6312 kHz, 8414.5 kHz, 12577 kHz, 16804.5 kHz.

These are the transmit center frequencies, if you set the center frequency in Black Cat GMDSS to 2000 Hz, then tune 2 kHz lower.

Some notes about comparing different GMDSS decoding programs:

One thing to consider when comparing programs is how they handle invalid decodes. Some GMDSS programs display decodes with bad ECC values, or other errors. By default, Black Cat GMDSS does not display messages with a bad ECC, although there is an option in the settings to display them, if you wish. Messages with invalid (failed parity check) characters in both positions are never displayed, but again some other programs may display them, even though there is no chance the message contents are actually valid. The raw number of displayed messages is not necessarily the only consideration when comparing programs.

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Last modified May 18, 2023