Tagged: P25

New Version of Digital Speech Decoder DSD+ 1.071 Released

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.

The FMP NFM demodulator tuned to a MotoTRBO signal.
The FMP NFM demodulator tuned to a MotoTRBO signal.

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:

  • Better tablet support
  • IDAS/NEXEDGE/Cap+/Con+/TIII trunk voice following
  • Per-call audio recordings
  • Other needed DSD+ upgrades
  • FMP upgrades
    • Squelch
    • Drift tracking
    • Selectable sampling rates
    • Adjustable windows sizes
    • TCP client/server mode (eliminates VAC / VB-C)
    • Multiple VFOs
    • Airspy support

Monitoring a Trunked P25 LSM Simulcast System with OP25 and an RTL SDR

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.

DSD+ Version 1.5 Released

Version 1.5 of Digital Speech Decoder Plus (DSD+) has been released. DSD+ is a popular Windows software tool used for decoding digital speech such as P25 with the RTL-SDR. The latest version comes with a simple GUI interface that has an event log that shows call target and source ID history and an audio waveform plot which can help determine if DSD+ is receiving audio correctly. This version of DSD+ has the ability to decode the following protocols.

  • D-STAR
  • NXDN4800
  • NXDN9600
  • DMR/MotoTRBO
  • P25 Phase 1
  • X2-TDMA
  • ProVoice

In addition to the above, the new version comes with an LRRP decoder and display program which should allow you to see on a map the GPS location of broadcasting radios.

DSD+ V1.51 can be downloaded from this link. The forum thread on RadioReference where the developer releases and discusses the DSD+ software can be found here.

This version of DSD+ comes with all the files needed to make it run already. To use DSD+ V1.5 simply extract the zip file into a folder and double click on DSDPlus.EXE. DSD+ will listen to your default audio device that is set in the Windows sound recording properties. Simply tune to a digital voice signal in SDR# or any other SDR receiver and set the output audio settings accordingly. To start the LRRP display program simply open LRRP.exe.

DSD+ V1.5 LRRP GPS Display
DSD+ V1.5 LRRP GPS Display

RTL-SDR Tutorial: Following Trunked Radio with Unitrunker

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.

You can download the latest version of Unitrunker here.

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.

Continue reading

RTL-SDR DSD Call Log Recorder

Programmer Tyler Watt has been working on software that automatically logs each call from an RTL-SDR running DSD (Digital Speech Decoder) and then stores it in a time stamped database as an mp3 file. There is also a web front end for the database which allows public users to search and play recorded calls.

Recently Tyler updated his code by rewriting it in PHP and making it multiplatform.

The old version of his web front end in action for his local P25 calls can be viewed here, and the newer one can be found here.

Improved Digital Voice P25 Decoding with DSD+

Over on Reddit we’ve seen mention of an upgraded Digital Speech Decoder (DSD) program, named DSD+. The original DSD is a program that can be used in conjuction with a SDR receiving program such as SDR#, and an audio piping program like VBCable to decode digital speech, such as P25 and DMR/MOTOTRBO.

DSD+ claims to have improved decoding and audio quality capabilities. An audio sample from a weak P25 sample can be found here for DSD+, and for comparison here for the old DSD.

DSD+ can be downloaded from this megaupload link.

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+)

DSD+ Output
DSD+ Output

EDIT: There is now a new version of DSD+ see http://www.rtl-sdr.com/dsd-version-1-5-released/.

New DSD Block Available for GNU Radio

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.”

Download the files from GitHub.

DSD is a Linux and Windows software program capable of decoding popular digital speech codecs such as APCO P25 and MOTOTRBO/DMR.

Via DangerousPrototypes

Radio Signal Identification Guide

NOTE: Recent changes to WordPress seem to have broken the audio on this page. Please use the new Signal Identification Wiki. 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 rtlsdrblog@gmail.com, 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). More sites with sample audio can be found at this list on dxzone.com. A very nice overview video of the HF spectrum by balint can be found here. There are also two paperback books: Technical Handbook for Radio Monitoring VHF/UHF (PDF Excerpt) & Technical Handbook for Radio Monitoring HF (PDF Excerpt) which have a very comprehensive list, description and images of many signals.


Sample Audio: Typical Frequency: 131.550 MHz Mode: AM Bandwidth: 5000-8000 Hz Description: Aircraft Communications Addressing and Reporting System (ACARS). Short messages sent to and from aircraft. Decoding Software: PlanePlotter, ACARSD Video Examples: [1], [2]
ACARS Packets

P25 Phase 1 (C4FM Modulation) (Encrypted)

Sample Audio: Typical Frequency: ~860 MHz, ~500 MHz + others Mode: NFM Bandwidth: 10000 Hz Description: P25 encrypted digital voice signal with C4FM modulation. Decoding Software: Digital Speech Decoder (DSD). Note, only unencrypted can be decoded. Video Examples:  [1], [2][3]
P25 Waterfall Example


Sample Audio: Typical Frequency: ~860 MHz Mode: NFM Bandwidth: 10000 Hz Description: Motorola digital voice signal known as MotoTRBO (pronouced Moto-Turbo). Decoding Software: Digital Speech Decoder (DSD). Note, only unencrypted can be decoded. Video Examples: [1], [2]
DMR/MOTOTRBO Signal Waterfall


Sample Audio: Typical Frequency: ~151 MHz, ~900-950 MHz Mode: NFM Bandwidth: 10000 Hz Description: Pager digital signal known as POCSAG. An acronym of Post Office Code Standardization Advisory Group. Decoding Software: PDW Video Examples: [1], [2]
 POCSAG/FLEX Pager Waterfall Image

Weather Balloon (Radiosonde) Vaisala RS92SGP

Sample Audio: Typical Frequency: ~400 MHz Mode: NFM Bandwidth: ~5500 Hz Description: Weather balloon (Radiosonde) telemetry data. Only transmits during a weather balloon launch. Decoding Software: SondeMonitor Video Examples: [1], [2]
  RS92SGP Radiosonde Waterfall Image

TETRA Downlink

Sample Audio: Typical Frequency: 380 – 430 MHz Mode: – Bandwidth: 25000 Hz 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. Thanks to Jenda for the submission. Decoding Software: osmocomTETRA Video Examples: [1], [2]

TETRA Downlink

Trunking Control MPT1327

Sample Audio: Typical Frequency: ~420 MHz Mode: NFM Bandwidth: 10000 Hz Description: Radio trunking control channel. Decoding Software: Trunkview, UniTrunker Video Examples: [1]

MPT1327 Waterfall Image

Trunking Control Motorola Type II Smartnet

Sample Audio: Typical Frequency: ~860 MHz Mode: NFM Bandwidth: 8000 Hz Description: Radio trunking control channel. Decoding Software: UniTrunker Video Examples:

Motoroal 2F1D Trunking Channel

Trunking Control EDACS96

Sample Audio: Typical Frequency: ~860 MHz Mode: NFM Bandwidth: 10000 Hz Description: Radio trunking control channel. Decoding Software: UniTrunker Video Examples:

EDACS96 Trunking Channel

Trunking Control APCO P25

Sample Audio: Typical Frequency: ~860MHz Mode: NFM Bandwidth: 12500 Hz Description: Radio trunking control channel. Decoding Software: UniTrunker Video Examples:

APCO P25 Trunking Channel


Sample Audio: Typical Frequency: ~144 MHz Mode: NFM Bandwidth: 10000 Hz Description: Audio frequency-shift keying (AFSK). Used by amateur radio hams for packet radio, Automatic Packet Reporting System (APRS) and telemetry. Decoding Software: QTMM Video Examples: [1]



Sample Audio: Typical Frequency: Marine Channel 87 – 161.975 MHz Marine Channel 88 – 162.025 MHz Mode: NFM Bandwidth: 12500 Hz OR 25000 Hz Description: Automatic Identification System (AIS). Used by ships to broadcast position and vessel information. Uses 9.6 kbit GMSK modulation. Decoding Software: ShipPlotter, AISMon (In the Files Section of the Yahoo Group) Video Examples: [1], [2]

AIS Waterfall

NOAA Weather Satellite (APT)

Sample Audio: Typical Frequency: NOAA 15 137.620 NOAA 18 137.9125 NOAA 19 137.100 Mode: WFM Bandwidth: 30000 Hz Description: NOAA Automatic Picture Transmission (APT) signal. Used to by the NOAA weather satellites to transmit satellite weather photos. Only transmits at certain times throughout the day when the satellite passes overhead at your location. Decoding Software: WXtoImg Video Examples: [1], [2], [3]
 NOAA APT Waterfall Screenshot

Stereo Wideband FM (WFM)

Sample Audio: – Typical Frequency: 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. Thanks to Tobby for the submission. Decoding Software: Unencoded Video Examples: [1], [2]

Amplitude Modulation (AM)

Sample Audio: – Typical Frequency: Long wave – 153 to 279 kHz Medium wave – 531 to 1,611 kHz in ITU regions 1 and 3 and 540 to 1610 kHz in ITU region 2. Short wave – 2.3 to 26.1 MHz Aircraft – 108 to 137 MHz Mode: AM Bandwidth: 10000 Hz Description: Amplitude Modulation broadcast audio radio station. Thanks to rtlsdr_is_fun for the submission. Decoding Software: Unencoded Video Examples: [1], [2]
 AM Waterfall

Weatherfax (HFFAX)

Sample Audio: Typical Frequency: HF ~3 to 16 KHz. Location dependant. Mode: Upper side band (USB) Bandwidth: ~1900 KHz Description: HF Weatherfax. Used by boats for weather reports. Also Kyodo News, a Japanese newspaper transmits entire pages via HFFAX. Decoding Software: FLDIGI Video Examples: [1], [2]

Upper Side Band Voice (USB)

Sample Audio: Typical Frequency: All HF band. Mode: USB Bandwidth: ~1900 Hz 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. Decoding Software: Unecoded Video Examples: [1], [2]

Over the Horizon (OTH) Radar

Sample Audio: Typical Frequency: All over HF Band Mode: – Bandwidth: - Description: Over the horizon radar. Used by governments for very long range radar systems. Decoding Software: Unencoded

Analogue PAL TV

Sample Audio: - Typical Frequency: Multiple Mode: PAL TV Bandwidth: 5 MHz Description: Analogue PAL TV. Color TV signal. Decoding Software: TVSharp Video Examples: [1]
 Analogue PAL TV

Digital Audio Broadcast (DAB+)

Sample Audio: No Audible Sound Produced Typical Frequency:  Multiple channels. Block 13F – 239.200 MHz Mode: DAB Bandwidth: 1,537 KHz Description: Digital Audio Broadcast (DAB+). A type of digital broadcast radio signal, containing multiple digital radio stations in the signal. Decoding Software: SDR-J Video Examples: [1]
 DAB+ Digital Audio Broadcast

Baby Monitor (NFM)

Sample Audio: - Typical Frequency: ~40 MHz, 49.5 – 50 MHz Mode: NFM Bandwidth: < 15 KHz Description: NFM signal from a baby monitor. Periodically bursts signal when no audio is detected. Thanks to Dean for some extra info. Decoding Software: Unencoded Video Examples: [1]

Digital Radio Mondiale (DRM)

Sample Audio: Typical Frequency: Below 30 MHz on HF, near other shortwave radio stations. Mode: USB Bandwidth: 10000 Hz Description: Digital Radio Mondiale (DRM). A form of international digital shortwave radio. Replaces AM shortwave radio. Thanks to Will P. for the contribution. Decoding Software: DREAM, SODIRA Video Examples: [1], [2]
 Digital Radio Monodiale Waterfall Digital Radio Monodiale Waterfall


Sample Audio: Typical Frequency: All over HF. Mode: USB Bandwidth: 2500 Hz Description: Standardization Agreement (STANAG) 4285. NATO standard for HF communication. Decoding Software: Sorcerer (Waring: Potential Virus Alert), Sigmira Video Examples: [1]
 STANAG 4285 Waterfall Example

GSM Downlink (Non-Hopping)

Sample Audio: Typical Frequency: 900 MHz and 1800 MHz Band OR 850 MHz and 1900 MHz Band Mode: – Bandwidth: 200 KHz Description: GSM Cell Phone Downlink (Non Hopping Signal). Audio sample used NFM mode. Decoding Software: Airprobe
 GSM Non Hopping Waterfall Image

GSM Uplink

Sample Audio: No Audible Sound Produced. Typical Frequency: ~890 MHz Mode: – Bandwidth: 200 KHz Description: Initial connection GSM signal sent from a cellphone. Decoding Software: -

GSM Downlink (Hopping)

Sample Audio: No Audible Sound Produced Typical Frequency: 900 MHz and 1800 MHz Band OR 850 MHz and 1900 MHz Band Mode: – Bandwidth: Each channel 200 KHz Description: GSM cell phone hopping. Decoding Software: -
 GSM Hopping Waterfall

“Japanese Slot Machine” (XSL)

Sample Audio: Typical Frequency: Between 4 MHz and 9 MHz Mode: USB? Bandwidth: - Description: Known as the Japanese Slot Machine. Thought to be data originating from the Japanese Navy. Decoding Software: Sigmira (But Cannot Decrypt) Video Examples: [1], [2]
 Japanese Slot Machine Waterfall

Automatic Dependent Surveillance-Broadcast (ADS-B)

Sample Audio: No Audible Sound Produced Typical Frequency: 1090 MHz Mode: – Bandwidth: 2 MHz Description: Automatic Dependent Surveillance-Broadcast (ADS-B). Used by aircraft to broadcast their latitude, longitude and altitude. Decoding Software: ADSB#, Dump1090, RTL1090 Video Examples: [1], [2], [3]

Cuban Numbers Station HM01

Sample Audio:  Typical Frequency: 11.530 MHz. Mode: AM Bandwidth:Description: (Previously Unidentified Signal 5). Numbers stations 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. Decoding Software: Information Here Video Examples: [1], [2], [3], [4], [5]

High Frequency Data Link (HFDL)

Sample Audio:  Typical Frequency:  HF Band Mode: USB (1440 Hz below center) Bandwidth: ~2800 Hz 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. Decoding Software: PC-HFDL Video Examples: [1], [2], [3]

Binary Phase Shift Keying (BPSK31)

Sample Audio:  Typical Frequency:  HF Amateur Band Mode: SSB Bandwidth: ~31 Hz Description:  A digital amateur radio mode based on Phase Shift Keying (PSK) modulation Thanks to Patrick for the submission. Decoding Software: Fldigi, MixW, HRD Digital Master 780, MultiPSK Video Examples: [1], [2][3]
BPSK Waterfall Example

AFSK Paging Link

Sample Audio:  Typical Frequency: 72-76 MHz 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.

Pulse Code Modulated (PCM) RC Toy Signal

Sample Audio:  Typical Frequency: 27.145 MHz, 72 MHz Description: (Previously unidentified signal 9). Identified in the comments section by W1BMW as a Pulse-code modulated (PCM) signal used for remote control (RC) Toys. Link to IQ file http://i.nyx.cz/files/00/00/09/99/999880_c640d91142db39ee7d57.zip?name=SDRSharp_20130613_113322Z_27186kHz_IQ.zip. Sample audio recorded in USB mode.

Overlapping RTTY Signals

Sample Audio:  Typical Frequency: HF band Description: Previously unidentified signal (11). Identified in the comments by various contributors as multiple overlapping RTTY signals sent by ham radios.
Unknown CW #3

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. Link to RR identification discussion from submission email. Thanks to Mike (VE3HER) for the submission.
x2 on iden

Funcube-1 Satellite

Sample Audio: Found Frequency: 145.950 – 145.970 MHz Mode: USB Bandwidth: ~2 kHz Description: The Funcube-1 is a Cubesat amateur radio satellite. Decoding Software: Funcube Telemetry Dashboard

Swedish Pocsag Minicall

Sample Audio: Typical Frequency: ~161 MHz Mode: NFM Bandwidth: 20 kHz Description: A short Pocsag 1200 signal used in electric plants and remote transformer and insulation stations. Thanks to Joni for the submission. Decoding Software: PDW Video Examples: [1], [2]

Unidentified Signals

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 rtlsdrblog@gmail.com.


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.


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.


Sample Audio:  Found Frequency: 152.652 MHz Description: Continuous signal. Audio sample recorded in NFM.


Sample Audio:  Found Frequency: 162.863 MHz Description: Continuous bursts. Audio sample recorded in NFM.


Sample Audio:  Found Frequency: 457.168 MHz Description: Audio sample recorded in NFM.


Sample Audio:  Found Frequency: 452.325 Mhz Description: Sent in over email. Sounds like Motorola Type II smartnet, but Unitrunker does not recognize.


Sample Audio:  Found Frequency: 154.646 MHz Description: Sent in over email. Repeats every minute.


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!


Sample Audio:  Found Frequency: 455 MHz Description: Sent in over email.


Sample Audio:  Found Frequency: 173.262 MHz Description: Sent in over email.


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.


Sample Audio:  Found Frequency: ~409.6 MHz Description: Sent in over email. Recorded in NFM mode.