Tagged: Automatic dependent surveillance broadcast

New product from FlightAware: A 1090 MHz Bandpass Filter for the RTL-SDR

FlightAware.com have released a new 1090 MHz bandpass filter that is intended for use with the RTL-SDR. FlightAware.com is a website that aggregates ADS-B aircraft location data from various contributors. The contributors are often users with RTL-SDR dongles running their PiAware software. By contributing to their service you gain access to their premium services for free.

The bandpass filter is available on Amazon for US customers for $19.95 USD and on eBay worldwide for $24.95 USD. This is the cheapest ADS-B filter we've seen yet. It comes in a metal case with SMA connectors, passes 980 MHz - 1150 MHz, has an insertion loss of about 1.65 dB at 1090 MHz and has about a 40dB drop outside the pass band. Over on their forums many users are reporting good results.

A bandpass filter blocks all frequencies apart from the range you are interested in, significantly reducing the effects of out of band interference. It is especially useful if you live near cell phone towers as these can easily interfere with the 1090 MHz frequency. 

FlightAware also sell an ADS-B antenna on Amazon for $44.95 USD and worldwide on eBay for $54.99 which may be of interest to some people.

An alternative ADS-B filter for the RTL-SDR is the one made by Adam 9A4QV. Adams filter uses LTCC filter technology which gives lower insertion loss, but a less sharp cutoff.

The FlightAware 1090 MHz ADS-B Filter
The FlightAware 1090 MHz ADS-B Filter
Filter Reponse Test Data
Filter Reponse Test Data

Creating a FIS-B ADS-B Weather Information Receiver for Pilots with an RTL-SDR

Recently a pilot wrote in to let us know about how he’s been using his RTL-SDR to receive real time FIS-B ADS-B weather updates in ForeFlight while flying in his plane. ForeFlight is an iOS app for pilots that helps with flight planning and provides access to important information like charts, real time weather reports and airport information. However, to access real time weather information usually you need to buy a $549 – 899 Stratus receiver. 

Now it is possible to use an RTL-SDR to receive the FIS-B weather information that is transmitted on the 978 MHz UAT frequency which is available only in the USA. UAT stands for Universal Access Transmitter and is similar to ADS-B transmitted at 1090 MHz, however UAT has some extra features for pilots compared to ADS-B. In addition to location information UAT provides a Traffic Information Service (TIS-B) which allows pilots to see what ground control sees on their traditional RADAR system. It also provides a Flight Information Service-Broadcast (FIS-B) which includes weather and other information. UAT is commonly used on small aircraft due to it’s lower cost and additional features. 

To receive UAT FIS-B weather information the pilot used dump978 on a Raspberry Pi 2. Dump978 is a UAT decoder, similar in operation to dump1090. He has also created a program called “Stratux“, which together with a WiFi adapter allows the decoded FIS-B data to be transmitted from the Raspberry Pi by WiFi to an iPad running ForeFlight. Running the software is as simple as piping the 978 MHz signal from rtl_fm into dump978, and then piping the decoded output of dump978 into stratux. Foreflight can then connect to the WiFi signal and work like it is connected to an expensive Stratus receiver.

In the video example below you can see some weather radar animations from FIS-B data received from the RTL-SDR shown on the ForeFlight screen at around 4:29 and onwards.

RTL-SDR, Rasperry Pi, WiFi dongle and portable battery pack for receiving UAT.
RTL-SDR, Rasperry Pi, WiFi dongle and portable battery pack for receiving UAT.
FIS-B UAT Weather Report received on Foreflight from a Raspberry Pi and RTL-SDR running dump978.
FIS-B UAT Weather Report received on Foreflight from a Raspberry Pi and RTL-SDR running dump978.

ADS-B Air Demo (ForeFlight)

 

Using a HackRF to convert ADS-B packets into Bluetooth packets for reception on your Smartphone/Tablet

HackRF experimenter Jiao Xianjun has recently posted about his new firmware which allows a single HackRF to receive an ADS-B data packet at 1090 MHz, and then retransmit it as a Bluetooth low energy (BTLE) packet at 2.4 GHz. A smartphone or tablet can then be used to view the ADS-B data. It appears that the system works by broadcasting several fake Bluetooth peripheral names as the received flight data, so there is no way to currently view the data on a map.

The firmware needs to be flashed into the HackRF RAM or ROM, and he provides instructions for this over on his post. The video below shows the HackRF and software in action on an iPad.

ADS-B to BTLE HackRF Relay
ADS-B to BTLE HackRF Relay
Air relay ADS-B to BTLE via single HACKRF in realtime

Tutorial on using an RTL-SDR for ADS-B on a BeagleBone Black from Make Magazine

Make magazine has recently released a tutorial and uploaded a video showing a nice overview on how to get an RTL-SDR set up for ADS-B decoding on a BeagleBone Black embedded Linux computer. In the tutorial and video they show you the parts you will need and show you how to compile and install the RTL-SDR drivers and dump1090 ADS-B decoder on the BeagleBone.

ADS-B decoding allows you to receive GPS and other information from aircraft in your vicinity. We also have a tutorial about ADS-B decoding available here.

The BeagleBone Black is a small embedded Linux computer, similar to the Raspberry Pi. It has enough computational power to run the RTL-SDR and ADS-B decoder. 

Monitoring FBI Surveillance Aircraft with ADS-B and an RTL-SDR

After reading an article by the Washington Post about FBI surveillance aircraft spotted in the air after the West Balimore riots, John Wiseman decided to look for more information about these aircraft. Fortunately, John had on his hands a database of about 2 months of ADS-B data that was collected by his continuously running RTL-SDR + BeagleBone Black ADS-B decoder set up.

From reports on the internet John found out that FBI aircraft squawked with 4414 or 4415 codes, and used call signs like JENNA or JENA. With this information John decided to take a look through his ADS-B logs to see if if he could find anything similar. Out of 15,000 aircraft he had tracked, he found 9 aircraft in his logs that matched the criteria, and saw that they did exhibit suspicious behaviour such as circling over LA for hours at a time. Then by looking up their FAA records of the tail numbers of the suspicious aircraft, he was able to discover that these aircraft where licensed to companies with names like NG Research, OBR Leasing, Aerographics Inc. and PXW Services which are suspected Department of Justice front companies. John also writes:

If you Google the tail numbers of aircraft registered to those companies, you start to find forum and mailing list posts (often at sites that tilt toward paranoid/conspiracy/right wing, but not always) with people discussing these specific tail numbers and linking them to the FBI. Some of the supposed evidence includes details of radio communications that people have heard, e.g. talking about “being on station” or using callsigns that start with JENNA, JENA or ROSS, which are supposedly used by the FBI. Other posts claim that DOJ/FBI surveillance aircraft often squawk 4414 or 4415 on their transponders.

An article from the startribune talks about the surveillance planes and says:

The planes use “persistent wide-area surveillance” to photograph large areas for hours at a time, Stanley said. The captured images allow authorities to go back in time, if necessary, to trace pedestrians and vehicles who come to their attention.

Other devices known as “dirtboxes,” “Stingrays” or “IMSI catchers” can capture cellphone data. Stanley said it’s still unclear what technologies have been used in the surveillance flights.

 

Possible FBI Surviellance Aircraft Path from flightradar24.com
Possible FBI Surviellance Aircraft Path from flightradar24.com

How coax cable loss affects ADS-B reception

Over on YouTube user Adam Alicajic has uploaded a video showing how coax cable loss affects the frame rate when receiving ADS-B. To do this test Adam uses a precision attenuator in between his ADS-B antenna and RTL-SDR dongle to simulate attenuation from coax cable loss. His results show that for every 1 dB of attenuation the frame rate drops by about 10%.

Coax cable loss for common type of cable can be estimated with calculators available at http://www.net-comber.com/cable-loss.html and http://www.arrg.us/pages/Loss-Calc.htm. RG-6 cable has a low loss at 1090 MHz of about 0.23 – 0.32 dB per meter, whereas RG58 has a loss of about 0.5 – 0.6 dB per meter and RG174 (stock antenna cable on most RTL-SDR units) has a greater loss of about 1.2 dB per meter.

Coax length loss contribution to the bad ADS-B reception

RTL-SDR vs. AIRSPY on ADS-B Reception: Round 2

A few days ago we posted about Anthony Stirk’s comparison between the RTL-SDR and the Airspy on receiving ADS-B signals. In his first test Anthony used an E4000 dongle, which is known to have inferior performance at the ADS-B frequency of 1090 MHz.

Now Anthony has done his test again, but this time with an R820T2 RTL-SDR. His results show that the R820T2 RTL-SDR is better than the E4000 RTL-SDR, but that the Airspy is still better than the R820T2 RTL-SDR. The R820T2 received at maximum distances more comparable to the Airspy, though still fell short of the Airspy by some 50 kms in some directions. Anthony’s writes that his distance seems to be mainly limited by geography so it is possible that in some other location the Airspy could out perform the RTL-SDR by a more significant distance.

The most interesting part of his last experiment was that over a 28 hour period the E4000 RTL-SDR received only a total of 2.9 million messages whilst the Airspy received a total of 10.3 million messages. In the new experiment the R820T2 received a total of 22.3 million messages whilst the Airspy received a total of 31 million messages, which is a little closer. However, with the R820T2 RTL-SDR, 3 million messages were unusable, versus only 31 unusable messages with the Airspy.

From these results it’s clear that the better design and more ADC bits in the Airspy can significantly improve ADS-B reception. However, there is a cost difference at $199 for the Airspy vs <$20 for the RTL-SDR. The Airspy cost may be soon less of a problem we are aware that an Airspy Lite version is in the works and that will probably cost around $99 USD.

In the future Anthony will do another test with no error correction enabled because the current version of the Airspy ADS-B decoder has no error correction whereas the RTL-SDR ADS-B decoder does. Those results may show that the Airspy is even better that shown here.

Update: Anthony ran the test again with a modified version of ADSB# with not error correction and obtained the following results which show that the Airspy receives about double the messages compared to the RTL-SDR:

Total Messages Received:
Airspy 65,150,313
RTL 32,973,049

Airborne Position:
Airspy 4,615,972
RTL 2,270,810

Unusable:
Airspy 533
RTL 635,549

Airspy vs R820T2 RTL-SDR on Maximum ADS-B Distance.
Airspy vs R820T2 RTL-SDR on Maximum ADS-B Distance.

RTL-SDR vs. Airspy on ADS-B Reception

With the recent release of ADSBSpy, an ADS-B decoder for the Airspy software defined radio, many people have been wondering how much better the Airspy is compared to the low cost RTL-SDR dongle at ADS-B reception. Over on his blog, Anthony Stirk has performed a test comparing an E4000 RTL-SDR with the Airspy.

In his test Anthony uses an A3 ADS-B antenna from Jetvision.de, and a HABAMP which is an LNA plus 1090 MHZ SAW filter. To create a fair test he used an antenna splitter and measured the reception of both dongles at the same time. He ran one instance of ADSB# for the E4000 RTL-SDR, and one instance of ADSBSpy for the Airspy over 24 hours and recorded the results.

Airspy vs E4000 RTL-SDR
Airspy vs E4000 RTL-SDR

The results showed that the Airspy had approximately 50 km more range compared to the E4000 in some areas. More interestingly the stats showed that the Airspy received approximately 7 million more ADS-B messages compared to the RTL-SDR.

While there is no doubt the Airspy will perform better, one thing to note about this test is that it used an E4000 RTL-SDR which is widely considered to have inferior performance at the 1090 MHz ADS-B frequency when compared to the R820T/2 dongles.

Airspy vs. E4000 RTL-SDR
Airspy vs. E4000 RTL-SDR