Thank you to Adrian (YO8RZZ) for writing in and sharing with us his article explaining how to use an SDR to set up a digital voice hotspot for digital voice modes supported by MMDVM such as D-Star, DMR, System Fusion, P25 and NXDN. Adrian notes that this is possible with any full duplex SDR such as the LimeSDR or PlutoSDR, or with a combination of simplex devices, such as a HackRF for transmitting combined with an RTL-SDR for receiving.
MMDVM is firmware that normally runs on an ARM microcontroller board such as the Arduino Due, and is designed to be interfaced with hardware radios via the microcontrollers built in ADC and DAC hardware.
In order to use an SDR instead of physical hardware radios, Adrian's article describes how a fork of MMDVM called MMDVM-SDR is used in his system as this allows the code to run on a normal Linux computer with an SDR. GNU Radio running on Adrian's own QRadioLink software is then used to create software ADC/DAC interfaces for the SDR and MMDVM-SDR to interface with, as well as providing a user interface.
QRadioLink used as the UI for MMDVM-SDR and GNU Radio
In this episode of Frugal Radio's ongoing SDR guide videos Rob demonstrates how you can use an RTL-SDR with DSDPlus to monitor DMR and NXDN digital voice radio communications. Rob writes:
With a simple Software Defined Radio (SDR) and some free or frugal software, you can monitor digital radio systems like DMR and NXDN in your area.
his video is a demonstration of how I set up DSDPlus to monitor DMR and NXDN networks, and shows how to modify the various files that help the software trunk track the system with your SDR.
More details with links to the software (DSDPlus) and hardware (1 x RTL-SDR v3) I used in this video can be found at https://frugalradio.com/monitor-dmr
f you are unsure about how trunking systems work, I suggest watching the overview at the beginning of Episode 6 - https://youtu.be/zuUTXHbUvpw
2020 SDR Guide Ep 7 : Trunk DMR & NXDN digital with DSDPlus and 1 RTL-SDR
Over on YouTube TechMinds has posted his latest video which shows an overview of the features available in OpenWebRX, and also how to set it up on a Raspberry Pi. OpenWebRX is software which allows you to access your SDR remotely via the internet or local network through a web browser. All major SDRs are supported including RTL-SDRs. The software includes a waterfall display, all the standard demodulators, as well as several digital decoders for DMR, YSF, NXDN, D-Star, POCSAG, APRS, FT8, FT4, WSPR, JT65 and JT9.
In the video TechMinds first demonstrates OpenWebRX in action, showing reception of HF SSB amateur radio signals, decoding FT8 and plotting received grids on a map, decoding and plotting APRS on a map and decoding YSF/DSTAR/DMR digital voice. After this demonstration he goes on to show how to set up the OpenWebRX server on a Raspberry Pi via the installation image.
Over on YouTube user radiosification has uploaded a video tutorial that shows how to decode, follow and listen to NXDN/IDAS trunking radio signals. NXDN/IDAS is a narrowband digital voice protocol commonly used with handheld radio terminals.
In the tutorial radiosification explains how to set up DSDPlus and its frequencies text file to automatically listen to and track conversations using the control channel. SDR# is initially used to find the NXDN control and voice channels, which are then entered into the text file. Using this method only DSDPlus and its corresponding receiver FMP is used. Trunking software like Unitrunker is not needed.
Radiosification also notes that the method he presents can also be used for other digital trunking systems such as P25 as well.
Over on YouTube user John Miller has uploaded a video showing how he receives NXDN digital audio using a combination of SDR#, the AuxVFO plugin and DSD+. He writes:
I have it set with 5 auxiliary VFO’s one for each channel of the Christian Co NXDN system from the Kelly Towers. I use VAC to route the audio from each VFO to DSD+ each VFO has it own DSD+ running. I then have all the DSD+ go into one output VAC and use that to run a feed on Broadcastify, The secret to running multiple DSD+ is to have separate install of it, so I have 5 DSD+ folders.
Over on YouTube user John Miller has uploaded a video showing an example of DSD+ decoding an NXDN96 voice signal. NXDN is a digital voice protocol by developed by Kenwood that is often used by public safety organizations.
John uses SDR# to receive the NXDN signal and then pipes the audio to DSD+ using Virtual Audio Cable for decoding.
NOTE: Recent changes to WordPress seem to have broken the audio on this page. Please use the newSignal Identification Wikiwhich has many new signals. Anyone can edit and improve the information on the pages on the wiki.
A guide to help you identify some amateur and utility digital radio signals and sounds which you may find on the frequency spectrum. Most of these have been received with an RTL-SDR software defined radio. I will be slowly adding more to this list over time. If you enable stereo mix and pass the sample audio to an appropriate decoding program the sample audio should be decodable for most samples.
If you would like to suggest a modification or contribute a sample, please send a sample, waterfall image and information about the signal to [email protected], or post in the comments. (Note I am currently backlogged with contributed signals, if I haven’t replied or added your signal yet it will be done within a month or two).
Description:Terrestrial Trunked Radio (TETRA), also know as Trans-European Trunked Radio is a professional mobile radio and two-way transceiver (walkie-talkie) specification. Modulated with π/4 DQPSK. Audio sample recorded in NFM mode.
Common – 87.5 to 108.0 MHz OIRT – 65 to 74 MHz Japan – 76 to 90 MHz Consumer Wireless Devices – ~860 MHz
Mode: WFM
Bandwidth: 30000 Hz
Description: Stereo Wideband FM signal. Used for typical broadcast radio, and in some wireless headsets and speakers. This particular signal is from an AKG headset.
Top signal is WFM transmitted with low amplification. Bottom signal is WFM transmitted with high amplification.
Description: Single side band, specifically upper side band. Used in the HF band by amateur radio hams and aircraft weather reports. Single side band saves bandwidth.
Description: (Previously Unidentified Signal 5). Numbersstations are thought to transmit encoded information for various spy agencies around the world. They are recognized by a voice reading a sequence of numbers or words. This is a Cuban Numbers Station which has a data portion and a voice portion. Sound sample recorded in AM mode.
Thanks to Andrew from the comments section for the ID.
Description: (Previously Unidentified Signal 2). An Aircraft Communications Addressing and Reporting System (ACARS) data link that aircraft use to communicate short messages over long distances using HF signals.
Thanks to Andrew from the comments section for the ID.
Description: (Previously unidentified signal 10). Identified in the comments section by Ronen as an Asynchronous Frequency Shift Keying (AFSK) pager link. It is easier to transmit the FSK pager signal to the transmitter site as AFSK.
Description: Previously unidentified signal (11). Identified in the comments by various contributors as multiple overlapping RTTY signals sent by ham radios.
Voice Frequency Telegraph
Sample Audio:
Typical Frequency: 7453.50 KHz USB
Description: Previously unidentified signal (13). VFT or Voice Frequency Telegraph is one of several systems for sending multiple RTTY signals over one voice-bandwidth radio channel.
Portable Traffic Lights
Sample Audio:
Found Frequency: 154.463 MHz
Description: Previously unidentified signal (17). Identified by Peter via email as being signals sent from portable traffic lights that are often used at roadworks.
X2 on iDEN
Sample Audio: –
Found Frequency: 154.463 MHz
Description: iDEN is an acronym for Integrated Digital Enhanced Network and is a technology developed by Motorola. It is a type of trunked radio with cellular phone benefits.
If you know what any of these signals are please write in the comments. You can also submit any unidentified signals you would like to be added to [email protected]
(1)
Sample Audio:
Found Frequency: 171.3 MHz
Description: Recognized by DSD as a NXDN96 signal, but is disputed in the comments section. (Possibly a bug in DSD).
(3) – ALE?
Sample Audio:
Found Frequency: HF Band
Description: Sound sample recorded in USB mode. Potentially some sort of 2G ALE signal. Similar signal shown in balints HF tour video. Possible a weather map transmitted from Tokyo as noted in the comments section by Syd, or 4xFSK from China as identified by K2RCN in the comments.
(4)
Sample Audio:
Found Frequency: HF Band
Description: Periodic pulses. Sound sample recorded in USB mode. Possibly a GlobeWireless signal as identified in the comments section by K2RCN.
(6)
Sample Audio:
Found Frequency: 152.652 MHz
Description: Continuous signal. Audio sample recorded in NFM.
(7)
Sample Audio:
Found Frequency: 162.863 MHz
Description: Continuous bursts. Audio sample recorded in NFM.
(8)
Sample Audio:
Found Frequency: 457.168 MHz
Description: Audio sample recorded in NFM.
(10)
Sample Audio:
Found Frequency: 452.325 Mhz
Description: Sent in over email. Sounds like Motorola Type II smartnet, but Unitrunker does not recognize.
(12)
Sample Audio:
Found Frequency: 154.646 MHz
Description: Sent in over email. Repeats every minute.
(14)
Sample Audio:
Found Frequency: 433 MHz
Description: Sent in over email.
Hello! I was listening in the 433MHz band and saw this blip (about 1-2sec) on the waterfall on 433.873 (Millville, MA). It repeats about every 30-50 seconds, though doesn’t seem to be the same every time. Maybe a wireless instrument of some type (weather or something?). The only clear sound of it I could get was with AM, about a 4.2kHz wide filter (rtl-sdr, gqrx linux). Any ideas? Thanks!
(15)
Sample Audio:
Found Frequency: 455 MHz
Description: Sent in over email.
(16)
Sample Audio:
Found Frequency: 173.262 MHz
Description: Sent in over email.
(18)
Sample Audio: None
Found Frequency: ~856 MHz
Description: Sent in over email.
The antenna has a Yagi pointed to West from 23.5° South latitude, 47.46° West longitude. The signal can be local or from the sky. The signal is horizontal polarized.
(19)
Sample Audio:
Found Frequency: ~409.6 MHz
Description: Sent in over email. Recorded in NFM mode.
