Decoding digital voice using DSD

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The digital radio voice communications are turning into some of the more frequently used among the radio spectrum. Such popularity may be largely explained by the different enhancements over the classic analogue alternatives. Nevertheless, regrettably, digital radios is pretty tough to come by since dedicated radio scanners are quite pricey and you cannot decode the digital signal without them. See, the digital radio systems are often encrypted which does make it challenging to decode them by a radio enthusiast. Still, the vast majority of digital radio users will not encrypt their systems since it results in significant lagging and will cost a pretty penny as well. 

You can stumble upon the most commonly used digital speech codec – APCO P25. DSD is capable of decoding it. 

Cheaper software solutions such as the RTL-SDR also may be used to decode the digital voice communication signals, so you will not need those pricey radio scanners to get started. Despite the fact that most tutorials will cover the RTL-SDR, Funcube dongle, HackRF, Airspy & BladeRF will work just fine as well. 

General recommendations

If you are unsure if the signal is supported in the first place, you can just scan through the different signals manually and check if DSD will start scrolling text. In this case, the decoding process will be triggered by the DSD at once. Nevertheless, do keep in mind that DSD will scroll text on trunking channels as well without being able to decode those. 

In order for DSD to decode properly, you will need a strong signal. Hence, you will need to make sure that you are using a good antenna. Don’t forget to set the RTL-SDR gain properly as well. 

DSD will be listening to the default device – the one you have recording sound. Ensure that virtual audio cable or VB-cable are indicated as default devices in the first place. If the wrong audio device is used, you will not see any text scrolling within DSD. 

Since DSD is still being actively developed, in most of the cases, it will not perform as well as a commercial digital radio, so there is that as well. 

In the event that you are looking for additional information on the matter, you are welcome to ham radio forums. Here, you will be able to get more data that will help you make the right call within the very least amount of time feasible.