In this weeks video Sarah from the SignalsEverywhere YouTube channel show us how to install and configure the OP25 software on a Linux machine. OP25 is a Linux based P25 digital voice decoder which works with RTL-SDR dongles. It is capable of decoding both Phase 1 and Phase 2 systems. Installation is fairly simple via an installation script, but it does take some time to install. After installation Sarah shows how to configure the software in order to properly follow a trunked P25 system. In order to help with importing talkgroup information from a premium RadioReference account Sarah has also created an automatic importer Python script which is very useful.
DragonOS is a ready to use Ubuntu Linux image that comes preinstalled with multiple SDR program. The creator of DragonOS, Aaron, uploads various YouTube tutorials. In his latest tutorial he shows how to install the latest version of the "Boatbod" OP25 development code for receiving P25 Phase 1 on Linux with the latest GNU Radio 3.8. In the video Aaron uses an RTL-SDR, but notes it could also work with other SDRs like the HackRF.
Thank you to M Khanfar for submitting another video where he demonstrates and explains how to easily send audio from your Linux PC over to an Android phone. This can be used to monitor the audio output of SDR programs like OP25 and GQRX remotely. The main piece of software used in his setup is the SoundWire Server and SoundWire Android App. SoundWire is described below:
Turn your Android device into wireless headphones / wireless speaker. Stream any music or audio from your PC to your Android phone, tablet, or other PCs. SoundWire does audio mirroring (audio cast). You can use any music player on your PC or laptop like Spotify, YouTube, or iTunes and stream low-latency live sound over WiFi directly to your Android device. Also works over 3G/4G cell networks or WAN.
M Khanfar's full tutorial on how to setup SoundWire can be found in the description of the video.
Last month we posted about Aaron's "DragonOS" project, which is a ready to install Linux ISO aimed to make getting started with SDR software easy by providing several programs preinstalled, as well as providing multiple video tutorials. Recently he's updated the build, this time basing it on Lubuntu 18.04 allowing for Legacy and UEFI support, along with disk encryption. The OS supports RTL-SDRs as well as the HackRF and bladeRF and probably supports most other SDRs via the SoapySDR interface.
In terms of software he's also added OP25 and bladeRF support. Other programs pre-installed include rtl_433, Universal Radio Hacker, GNU Radio, Aircrack-ng, GQRX, Kalibrate, hackrf, wireshare, gr-gsm, rtl-sdr, HackRF, IMSI-catcher, Zenmap, inspectrum, qspectrumanalyzer, LTE-Cell-Scanner, CubicSDR, Limesuite, ShinySDR, SDRAngel, SDRTrunk, Kismet, BladeRF.
His DragonOS YouTube tutorial channel is also growing fast, with several tutorials showing you how to use DragonOS to perform tasks like listen to trunked mobile radios, use QSpectrumAnalyzer with a HackRF, receive NOAA APT weather satellite images, retrieve cellular network information via a rooted Samsung Galaxy S5, create a ShinySDR server with rtl_433 and how to capture and replay with a HackRF.
Most police departments is the USA have now upgraded or are in the process of upgrading their radio systems to P25 Phase 2 digital radio. The frequencies can easily be received with an RTL-SDR, but a decoder is required to be able to actually listen to the voice. Software like SDRTrunk and DSDPlus can decode P25 Phase 1, but at the moment the only software that is capable of decoding P25 Phase 1 AND 2 is a program called OP25. However, OP25 has a reputation of being fairly difficult to set up as it does not have a simple to use GUI, and requires Linux.
Over on John's Tech Blog, John has uploaded a very helpful step by step tutorial that should help with those trying to get OP25 to work. The tutorial assumes that you have Ubuntu 18.04 already installed, and then starts from downloading and installing OP25. The next steps involve setting up OP25 for the particular system in your area, which mostly involves just editing a spreadsheet to input frequency data from radioreference.com. John also mentions that he's been able to get OP25 running perfectly on a Raspberry Pi 3 B+ as well, with less than 40% CPU usage.
In the video below John reviews some of the steps, and shows OP25 running and decoding voice.
APCO P25 is a digital voice signal and is commonly used like public safety departments such as police and fire. With an RTL-SDR and the open source Linux based OP25 decoder these signals can be decoded, assuming they are unencrypted. Software like DSD+ can also be used, but OP25 can supposedly decode more systems. Before the RTL-SDR, hardware scanners like the $~360 USD Uniden BCD996T digital scanner radio were typically used.
Over on YouTube user Rob Fissel has uploaded a video showing a comparison between an RTL-SDR using the OP25 decoder and a Uniden BCD996T. Both radios are used to decode a weak P25 Phase 1 LSM signal. He uses a Scantenna antenna with an antenna splitter to run both radios at the same time. His results show that even though the constellation is poor, OP25 does a good job at decoding the signal and producing voice, whereas the BCD996T doesn’t even manage to hear the control channel.
Over on YouTube user jdlucas78 has uploaded a video showing a P25 LSM modulated digital voice signal being decoded by the Osmocom OP25 software for Linux. Although DSD and DSD+ can decode P25 voice, it seems that the Osmocom OP25 software is better at decoding P25 signals as it implements better error correction algorithms.
Over on the RadioReference forums there is a thread discussing the use of the OP25 decoding software which can be found here. There is a post in the thread that shows an easy Linux install procedure for the OP25 software.