Thanks to Steve K2GOG of The Hudson Valley Digital Network (HVDN) for submitting his post on how to create a wireless display for Pi-Star. Pi-Star is a pre-built Raspberry Pi image for amateur radio users experimenting with digital voice communications like D-STAR and DMR. They write that it can be used for applications such as a "single mode hotspot running simplex providing you with access to the increasing number of Digital Voice networks, [or a] public duplex multimode repeater".
Pi-Star is compatible with serial based LED displays with built in GUIs like the Nextion. The displays are usually connected directly to the Raspberry Pi, but Steve wanted to use the display remotely. To do this he used a simple and inexpensive 70cm band HC-12 wireless serial port adapter. With the wireless adapters connected to the Pi he was able to see the pulses in SDR# via his RTL-SDR to confirm that the wireless serial signal was being sent. He then connected the second wireless adapter to the Nextion display via a few diodes to drop the voltage, and was able to get the display updating as if it was connected directly.
In the post Steve mentions that HVDN are also giving away an HC-12 and RTL-SDR to the first person to submit some progress with this idea.
Thanks to Tony C who wrote in and wanted to share a method that he's found to listen to multiple DMR digital voice channels in Linux. DSD+ is a Windows program that can be used to decode DMR. Although for Windows it is possible to use in Linux via the emulator known as Wine, and pipe the digital audio to it from GQRX. In the quote below, DSD+ "FL" is short for "Fast Lane" which is DSD+'s paid beta service that you can join to get newer code with more features. Tony writes:
I believe that can bridge the gap between using Linux with the ease of use programs of windows. As I am sure we both can attest that setting up trunk tracking / anything SDR is not as easy on Linux as it is on windows. For example, DSDplus FL makes it extremely easy to identify/decode DMR networks. There are similar things that can be done on Linux, but as I stated, it isn’t as easy to setup.
So the method that I setup and have been using successfully, using Ubuntu and a HackRF, setting up DSDplus 2.98 on wine, that gets audio piped from GQRX using a virtual sink as outlined in https://www.hagensieker.com/wordpress/2018/04/29/dsd-in-ubuntu-18-04/. It was a great blog, but I felt that it was incomplete when trying to get all the voice traffic passed on a network, as it only works on 1 channel at a time.
So I found the control channel for the network and created 5 bookmarks in GQRX and gave them the tag “DMR”. From there I downloaded gqrx scanner https://github.com/neural75/gqrx-scanner followed the install and setup instructions. From there I activated the scanner and GQRX will cycle through the frequencies and when voice traffic is passed, it will stop, and DSDPLUS via wine will decode and record the audio.
[The screenshot] example was for P25, but it has worked in connect+ as well, the only thing is that you cannot bookmark the control channel. I know other options exist out there such as SDRtrunk / op25 which I have used, but I believe this provides a good alternative to those who have used windows and are comfortable with the ease of use of dsdplus FL but want to be on the Linux OS.
Over on YouTube user Tech Minds has uploaded a useful video which shows how to set up DMR decoding with SDR#, VB-Cable, DSD+ and an RTL-SDR dongle. He also uses the DSD plugin for SDR# which makes controlling the command line DSD+ software a little easier. If you are interested we also have a short tutorial on DMR/P25 decoding available here. The video starts from downloading and installing the software, and explains every step very carefully, so it is a very good starting video for beginners.
DMR (aka MotoTRBO or TRBO) is a digital voice protocol used by Motorola radios. Software like DSD+ is required to listen to it, but it can only listen in if the signal is unencrypted.
Tech Minds has also uploaded several other tutorial videos to his channel over the last few months including guides on how to set up the ham-it-up upconverter, ADS-B tracking, using a Raspberry Pi to create a FM transmitter and more.
How To Setup SDR # Sharp To Decode DMR Digitial Using DSD Plus And An RTL SDR Receiver on Windows 10
At the end of last month we uploaded a post highlighting the SDRAngel software, which is a general purpose SDR program with some interesting features such as built in digital speech decoders for DMR, D-Star and Fusion. This avoids the need to pipe audio into a separate digital speech decoder program such as DSD+. SDRAngel also has transmit capabilities which makes it useful for SDRs such as the HackRF, PlutoSDR, LimeSDR etc.
The latest version of Digital Speech Decoder+ (DSD+) has just been released, bringing it up to version 1.071. There appears to be no changelog, so we are unsure as to what is new, but one obvious change is that they now include a new program called FMP which is a simple NFM demodulator, similar to rtl_fm, although it does have a GUI with point and click tuning. FMP can be used as a replacement for SDR# or similar software, and is especially useful to use on low end devices such as netbooks.
An active discussion on the latest release of this software can be found in this thread on the RadioReference.com forums.
DSD+ is a Windows program which can be used to decode and listen to digital voice protocols such as D-STAR, NXDN4800, NXDN9600, DMR/MotoTRBO, P25 Phase 1, X2-TDMA and ProVoice with an RTL-SDR or other radio. On some DMR systems you may also be able to use the included LRRP software, which allows you to view the GPS locations of broadcasting radios. The last major release was version 1.05.
The DSD+ team are now also offering a “fast lane” early access program, which for a small donation will allow you to have early access to new and upcoming DSD+ features. They aim to release a new update to donators every 7 to 30 days, while stable public releases will continue to be released every 4 to 6 months. The donation costs $10 for one year of early access, and $25 for lifetime updates. Some features they are currently working on include:
The popular trunking decoding software Unitrunker now supports the RTL2832U R820T RTL-SDR directly in its new version. This means that extra SDR receiver software like SDR# is no longer required to use Unitrunker.
In a normal radio system, one company (or talkgroup) might use a single frequency for radio communications. However, this is very inefficient as the frequency may not be in use for the majority of the time. In a trunked radio system, a small set number of frequencies are shared between a large number of talkgroups. Each radio receives a special computer controlled control channel. The control channel determines a vacant frequency that a particular talkgroup should use. This helps to make radio frequency allocations more efficient.
Because a talkgroup might switch between various frequencies often, it can make listening to a conversation difficult for radio scanners. Unitrunker can be used to decode the control channel and follow a voice conversation as it hops across various frequencies. With two RTL-SDR dongles you can set up a trunking receiver station with just Unitrunker. What follows below is a tutorial on how to set this up.
To run DSD+. you will need to place an MP3 encoder file lame_enc.dll into the same folder as the dsd.exe executable. This file is not included with DSD+ due to licencing. For Windows, lame_enc.dll can be downloaded from http://lame1.buanzo.com.ar/#lamewindl (Mega Mirror). Download the ZIP option, and then copy the dll file into the same folder as DSD+.
If you don't know how to use DSD, see our tutorial on using DSD here, and if desired simply use DSD+ instead of the original DSD. (Note cygwin is not required for DSD+)
The popular digital speech decoder (DSD) software has now been wrapped into a GNU Radio Companion block. Previously, DSD required use of virtual audio cables to get decoding to work with GNU Radio, but now the signal audio can be passed directly into this block.
Luke Berndt from the HackRF-dev forums has posted his work to make the functionality of DSD available to GNU Radio users in the form of a GRC block. “I have been playing around a bit and found an easy way to receive and playback digital LMR. More and more of the radio systems are going from narrow band FM to Digital. This makes it tough to listen to them on GQRX. DSD is a great program which can decoded the audio you get when you tune in a system in GQRX, but you either have to run it on another machine with a audio cable in between or figure out how to do a virtual audio cable on your machine.
Luckily, someone wrapped the DSD libraries so they can be accessed as GRC blocks. I have put together a GRC file and a Python program that make it a little easier to use the block.
If you have a chance, give them a try and let me know if they work. There is a good chance I have messed up the values in the filters or else where, but I have gotten clean audio out of it.”