Over on his YouTube channel Tall Paul Tech has uploaded a video that demonstrates the FM (frequency modulation) capture effect. Apart from the costs and difficult logistics to change from AM to FM worldwide, the FM capture effect may be one additional reason as to why aircraft still choose to use AM modulation for communications instead of FM.
The FM capture effect is a phenomenon that occurs when two FM transmitters transmit on the same frequency at the same time. What will happen with FM is that the stronger of the two transmissions will be the only one heard, with the weaker one totally muted. This is in contrast to AM where both signals can be heard, albeit garbled like two people talking at the same time.
With aircraft this is important as for example if some aircraft accidentally leaves a blank transmission open, another aircraft can still transmit on top of the blank transmission and still be heard. Or allowing air traffic control to hear if multiple aircraft are trying to transmit at once, and handle communications appropriately based on urgency. The disadvantage is that without the capture effect, AM is more prone to interference from interference and atmospheric noise like lightning.
In his demonstration Paul uses two HackRF's with their clocks linked and an RTL-SDR to simulate two transmitters and a receiver.
Aircraft transmit multiple types of radio signals, including ADS-B and VDL2. ADS-B (Automatic Dependent Surveillance-Broadcast) is an air traffic surveillance technology that enables aircraft to broadcast their GPS position and other data. VDL2 (VHF Data Link Mode 2) is a digital VHF signal, allowing pilots to exchange text information with ground controllers and/or airline ground support. VDL2 is not designed to provide real-time positional data like ADS-B; however, positional information is often broadcast, and the VHF signals can propagate over longer distances.
He also added the "Flight controls on RTL 1090XHSI" software, which allows users to view a simulation of an aircraft cockpit, using real-time ADS-B data from the RTL-SDR.
Pilots of RC planes and drones need to be aware of the area they are flying in, to make sure that they stay well out of the path of manned aircraft. However, this can sometimes be difficult with aircraft like police helicopters that could rapidly show up anywhere. Drones typically do not have ADS-B transmitters due to size/weight and price, but it is still possible for drone pilots to use ADS-B receivers to make their flying safer.
Over on YouTube user xjet has come up with a solution involving the use of a portable ADS-B alarm for drone pilots. The ADS-B receiver consists of a 3D printed enclosure containing a Raspberry Pi Zero 2W, LCD screen and an RTL-SDR dongle connected to an ADS-B whip antenna. xjet notes that when his code and 3D enclosure are finalized, he will release the design for free as open source over on http://www.rcmodelreviews.com.
The idea behind the ADS-B alarm appears to be that drone pilots will receive an alarm when they are within the vicinity of an aircraft. Assuming the drone is not too far away from the pilot (as rules specify drones must be flown within visible distance) the alarm being next to the drone pilot should be sufficient. xjet notes that we cannot rely on live ADS-B aggregation websites like FlightRadar24 due to their censorship of certain aircraft like police, military and some private jets, or due to possible lack of coverage, so a local receiver will be a better solution.
After more than two years of development and testing the ADSB alarm for RC plane and drone flyers is almost ready to go. I will be posting the full build details including an SD-Card image, source code, wiring diagrams and STL/DWG files for the case to the RCModelReviews website in the next week or so. This is a totally open-source project which I give freely to the hobby community so as to increase the levels of safety associated with our activities.
It is through the use of this technology that we can show how taking practical steps towards ensuring safety is every bit as important (if not more so) than blindly following regulations written by those who have probably never even flown an RC plane or drone themselves.
Over on YouTube we've found an interesting project by RingingResonance where he's created a simulated traditional radar scope using a real analog radar scope tube, and ADS-B data gathered from an RTL-SDR running dump1090 on a Raspberry Pi 3B.
The project uses a real radar scope tube which is controlled by SPI signals sent from the Raspberry Pi into a DAC, which is in turn connected to the analog radar scope. RingingResonance has uploaded the open source code to GitHub. He notes that the code currently pushes the Raspberry Pi 3 to it's limits, so the sweep speed is limited.
Today news has come out that ADS-B Exchange (ADSBx) founder Dan Streufert has sold ADSBx to a private firm called JETNET for (an estimated) $20 million. Dan was the sole owner of ADSBx, and after the sale he remains employed by JETNET. JETNET is a firm that provides aviation market intelligence to business customers.
UTICA, NY - JETNET, a leading provider of aviation data and market intelligence, announced today that it acquired ADS-B Exchange, one of the world’s largest networks of ADS-B/Mode S/MLAT feeders and providers of real-time and historical flight data. The acquisition is the second of what the company anticipates will be several future acquisitions as JETNET expands its data-driven product offerings for the aviation industry.
Founded in 2016 by Dan Streufert, ADS-B Exchange aggregates approximately 750,000 messages per second worldwide via receivers hosted by aviation enthusiasts around the world. The acquisition of ADS-B Exchange will enable JETNET to expand its flight data solutions with real-time information.
“ADS-B Exchange was founded as the go-to resource for aviation and flight-data enthusiasts,” said Dan Streufert, President and Founder of ADS-B Exchange. “Joining forces with JETNET is the perfect match as we look to meet the business needs of our users while maintaining our enthusiast roots and unfiltered data. With a long history of providing highly valuable data to the aviation industry, JETNET offers the resources we need to accelerate our growth.”
Like JETNET, ADS-B Exchange serves numerous constituents across the aviation industry, including Maintenance, Repair, Overhaul (MRO), airport operations, and aircraft leasing. In addition, its real-time data is used by dozens of commercial customers across numerous end markets, including aerospace & defense, government, research/academic, and financial services.
“We are committed to providing our customers with innovative product offerings which provide the information and intelligence they rely on to make critical business decisions,” said JETNET CEO Derek Swaim. “We’ve long admired ADS-B Exchange and know how strategic the company’s real-time data offerings are to the aviation industry. Dan has done an incredible job building a fast-growing business that customers love. We believe he, and the ADS-B Exchange platform, will bring significant value to our customers.”
About JETNET
As a leading provider of aviation market information, JETNET delivers comprehensive and reliable business aircraft research to its exclusive clientele of aviation professionals worldwide. JETNET is the ultimate source of information and intelligence on the worldwide business, commercial, and helicopter aircraft fleet and marketplace, comprising more than 110,000 airframes. Headquartered in its state-of-the-art facility in Utica, NY, JETNET offers comprehensive, user-friendly aircraft data via real-time internet access or regular updates. JETNET is a portfolio company of Silversmith Capital Partners.
ADSBExchange.com is an open source aggregator of ADS-B aircraft tracking data, contributed by volunteers who are all mostly running RTL-SDR radio dongles and Raspberry Pi based feeders. ADS-B data is transmitted at 1090 MHz and can be used to track aircraft movements.
Outrage over the sale has been expressed on Discord by various ADSBx open source co-developers who objected to the sale and appear to have received no compensation from the deal. The outrage has resulted in some co-developers actively encouraging that volunteer feeders remove their station from the ADSBx network. Several hundred of the over 9000 feeders have already disconnected their feeding stations, and the count is dropping (at the time of this post there were 9234 feeders).
Unlike similar ADS-B aggregators like FlightAware, FlightRadar24 and RadarBox, ADSBx is open source and promises to never censor the ADS-B data of billionaires, political leaders, military, police or other sensitive private aircraft. This has caused discussion over whether this free speech absolutist stance is either less or more moral. At the moment it is unclear if the acquisition will result in any ADSBx censorship policies changing.
Famously the @elonjet account (now @ElonJetNextDay) on Twitter used data from ADSBx. This account was used to automatically tweet out the location of Twitter owner Elon Musk's private jet in real time. The @elonjet account along with the @adsbexchange account was banned from Twitter shortly after Elon Musk's child had an altercation with a stalker. Legal action was threatened against @elonjet and "organizations who supported harm to [Elon Musk's] family" which could imply that ADSBx is in the legal action firing line.
While the sale may be discouraging to some, the project is still entirely open source, so it seems that only the branding and rights to the data collected have been sold. The following is entirely speculation on our behalf, but given that ADSBx was likely not very profitable and struggling to cover operating costs from donations only, and the threat of substantial legal action being taken against it's sole owner, the sale seems like the smart decision for the founder. We hope that the co-developers will receive some fair compensation as well.
ADS-B Exchange has been key to projects like "Dictator Alert" which tracks the real time location of the private jets of known dictators.
The Organized Crime and Corruption Reporting Project (OCCRP) has also made use of ADS-B Exchange data in the past to uncover the role that US civilian aircraft contractors are playing in the East African "kill chain".
Media have also used ADS-B Exchange to track the movements of the military aircraft like Black Hawk Helicopters and CBP Predator drones that were used to monitor crowds during the George Floyd protests.
SDRangel is a free open source software defined radio program that is compatible with many SDRs, including RTL-SDRs. SDRAngel is set apart from other programs because of it's huge swath of built in demodulators and decoders.
Thank you to reader Jon for writing in and noting that SDRangel has recently been released for Android as a free Google Play download. This is an amazing development that could open up many doors into portable decoding setups as the Android version supports almost every decoder implemented on the desktop version. Jon writes:
It includes most of the functionality of the desktop version of SDRangel, including:
AM, FM, SSB, Broadcast FM and DAB, AIS, ADS-B, Digital Voice (DMR, dPMR, D-Star, FreeDV), Video (DVB-S, DVB-S2, NTSC, PAL), VOR, LoRa, M17, Packet (AX.25), Pager (POCSAG), Radiosonde (RS41), Time signal (MSF, DCF77, TDF and WWVB) modems.
RTL SDR, Airspy, Airspy HF, LimeSDR, HackRF and SDRplay support via USB OTG as well as networked SDRs
2D and 3D signal analysis in both time and frequency domain with statistical measurements of SNR, THD, THD+N, SINAD, SFDR and channel power
Satellite tracker, star tracker, maps and rotator controller
It should work on Android 6 and up. It’s a straight port of the desktop application, so although it will run on a phone, probably best used on a large tablet with a stylus or mouse.
It also appears that the Twitter account for ADS-B Exchange @ADSBexhchange itself has been suspended too, as well as various other flight tracking Twitter bots that were using data from ADS-B Exchange. Elon Musk's tweet indicates that legal action is being taken against "Sweeney & organizations who supported harm to my family". It is unclear if this implies that legal action will be taken against ADS-B Exchange.
Elon Musk's Real-Time Doxxing Tweet
ADS-B (Automatic Dependent Surveillance–Broadcast) is a radio signal that is required to be broadcast by all aircraft for the purposes of air traffic control and collision avoidance. The ADS-B signal provides real time unencrypted location information that anyone with a low cost radio receiver like an RTL-SDR and cheap computer like a Raspberry Pi can receive, decode and turn into a live map of aircraft in the surrounding area.
ADS-B Exchange is an ADS-B aggregator that collects ADS-B data received from volunteers all over the world that are running RTL-SDR and other SDR dongles or radios operating as ADS-B receivers. Compared to more commercial flight tracking services like FlightAware and FlightRadar24 (who also make use of volunteer stations), ADS-B Exchange guarantees that they will not censor the tracking of military, police or private jets. This has generated debate in the past over whether this philosophy is either more moral or less moral.
ADS-B Exchange has been key to projects like "Dictator Alert" which tracks the real time location of the private jets of known dictators.
The Organized Crime and Corruption Reporting Project (OCCRP) has also made use of ADS-B Exchange data in the past to uncover the role that US civilian aircraft contractors are playing in the East African "kill chain".
Media have also used ADS-B Exchange to track the movements of the military aircraft like Black Hawk Helicopters and CBP Predator drones that were used to monitor crowds during the George Floyd protests.
Previously Elon Musk indicated that he would not ban the account following his private jet, however after the stalker altercation he appears to have rapidly changed his tune. Even without the Twitter bot, private jets can easily be tracked via ADS-B Exchange so any dedicated person could still gather this information without too much hassle. So it seems likely that legal action will be taken against ADS-B Exchange as per Elon's tweet. Other ADS-B data aggregators like FlightRadar24 and FlightAware should be safe from legal action as they do censor private aircraft upon request. Hopefully ADS-B exchange has prepared for this legal battle, which was probably an inevitable unfortunate outcome from their policy. If not from private jet owners, then the military or police would likely eventually take action if the data ever became a problem.
Thank you to James Mainwaring for letting us know about the latest update to his "ADS-B Radar (RTL-SDR)" Android App. The update brings an Open Street Map (OSM) display, allowing for aircraft to be directly plotted on the map.
As before the app works with an RTL-SDR directly connected to the Android device, and also has a radar like display.
James also has other apps on the Google Play store for FM Radio, Airband and Ham Radio listening.
