Thank you to Tomasz Lemiech for writing in and sharing with us the release of his new software "dumphfdl". Tomasz is the author of dumpvdl2 and also maintains RTLSDR-Airband. Regarding dumphfdl Tomasz writes:
dumphfdl is a multichannel HFDL decoder for Linux. HFDL (High Frequency Data Link) is a protocol used for radio communications between aircraft and a network of ground stations using high frequency (HF) radio waves. Thanks to the ability of short waves to propagate over long distances, HFDL is particularly useful in remote areas (eg. over oceans or polar regions) where other ground-based communications services are out of range. While many aircraft carriers prefer satellite communications these days, HFDL is still operational and in use.
Available HFDL decoding applications typically run on Windows and take an audio signal on input. The signal has to be delivered to the decoder via a physical cable from an external shortwave receiver or via a virtual cable from an SDR. This makes these apps inherently single-channel. This shortcoming does not apply to dumphfdl which interfaces directly with the SDR, so no pipes or virtual audio cables are needed. The program can decode multiple HFDL channels simultaneously, up to available CPU power and SDR bandwidth (there is no fixed channel count limit).
dumphfdl uses SoapySDR library (https://github.com/pothosware/SoapySDR) to communicate with the radio. Any HF-capable receiver for which a SoapySDR driver exists, should work. I have tested it briefly with an RTL-SDR v3 dongle in direct sampling mode. While I had a bit of a success with it, HFDL signals are often quite weak, so a real HF radio (like SDRPlay RSP1A or Airspy HF+) gives much better results (more decoded messages).
The program may log decoded messages to a file or send them over the network for external processing and storage.
HFDL messages often contain diagnostic data accompanied with aircraft position information. The program may extract this data from decoded messages and provide a positional data feed for external plane tracking apps (eg. Virtual Radar Server). An example screenshot from VRS is attached - taken after about 2 hours of decoding eight HFDL channels spread across three HFDL subbands: 6.6, 8.9, and 10.0 MHz with two dumphfdl instances on two radios - RSP1A and Airspy HF+. Definitely a nice way to expand the coverage of a home ADS-B radar :-)
Refer to the README.md file in the project repository for more details. The program is still under development, so new features and further improvements might be expected in subsequent releases.
dumphfdl - decoded aircraft positions plotted on a map
In the previous episode Rob from the Frugal Radio YouTube channel showed us how to decode HF ACARS using PC-HFDL and an HF capable SDR such as the Airspy HF+. In that episode he mentioned that it is possible to decode HF ACARS using a WebSDR as well.
In this weeks episode, Rob shows us how to do just that, making use of WebSDR receivers and the PC-HFDL software. Like the previous episode we see how to plot the aircraft HF ACARS position data on Google Earth and how to read and interpret some example messages received.
In Rob's latest episode of his excellent aviation communications series on his Frugal Radio YouTube channel he shows how to decode aircraft HF ACARS (HFDL) using a software defined radio. HFDL is short for "high frequency data link", and is a method aircraft use for sending text and data communications to ground stations. It is an alternative to VHF or satellite ACARS communications methods.
In the video he shows how he's been able to receive HFDL from all over the world using a simple HF dipole antenna and an Airspy HF+ Discovery. He goes on to show how to find HFDL signals, and how to decode signals using SDR# and the PC-HFDL software. Finally he shows examples of aircraft received, and how to interpret some of the information being received, including location information.
How to decode HF ACARS (HFDL) free with your SDR - Monitoring Aviation Communications Episode 8
In his latest YouTube video Tech Minds shows how to decode HF ACARS (HFDL) with an SDRplay RSPdx. Tech Minds initially explains what HFDL is, and how it is typically received via special aviation radios. He goes on to show how we can decode it from home with any HF capable SDR, and a program called PC-HFDL. Finally he explains how to set up a Google Earth file that can display the aircraft location data that is provided in some HFDL messages.
Over on YouTube user Shortwave Bavaria has uploaded a video that demonstrates HFDL reception. HFDL is short for High Frequency Data Link and is a signal used by aircraft to communicate short messages with ground stations over long distances. It is often used in place of VHF ACARS when flying over oceans.
In his video Shortwave Bavaria uses a 26.5m end fed wire, and a Cloud-IQ SDR. But we note that any HF capable SDR can be used to receive HFDL. SDR-Console V3 is used as the receiver, and MultiPSK Professional edition as the decoder. Many HFDL messages contain location data, so aircraft can be plotted on a map and he demonstrates this using Google Earth. In the video he notes how amazing it is that flights from across the globe can be received with his set up.
Amazing Decoding HFDL reception with SDR over central Europe
Over on YouTube icholakov has uploaded an informative video that gives an overview of the main communication modes that aircraft use from HF to UHF. In the video he also gives examples of those modes being received and decoded with an SDR.
The modes that he explains and demonstrates are VHF voice, VHF ATIS automated weather, ACARS short data messages, HF voice, HF automatic weather, HF data selective calling (SELCAL), HF data link (HFDL) and UHF ADS-B aircraft positioning.
Monitoring airplane communications (aviation radio signal monitoring via sdr)
Over on YouTube user k2nccvids has posted two videos showing how he was able to decode High Frequency Data Link (HFDL) packets using the RTL-SDR, Ham-it-up upconverter, MultiPSK and HFDL Display. HFDL is a service similar to ACARS but sent over HF frequencies. It is used to sent short messages to and from aircraft and ground stations.
In the first video k2nccvids uses MultiPSK with the RTL-SDR directly and also uses the add on software HFDL Display to more clearly view received HFDL packets. In the second video he uses SDR-CONSOLEv2 to monitor three HFDL frequencies simultaneously, with MultiPSK and HFDL Display still being used for decoding and display.
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.
