Category: Airband

New ADS-B Filter with Built in Bias Tee Available

Adam who is the manufacturer of the popular LNA4ALL low noise amplifier (LNA) that is commonly used with the RTL-SDR has come out with a new product for ADS-B enthusiasts. The product is an ADS-B filter with a built in bias tee for providing phantom power. Adam previously sold an older version of the ADS-B filter that came without the bias tee.

The bias tee allows you to inject DC power into the coaxial cable in order to easily power an LNA (like the LNA4ALL) or other device that is placed near the antenna. The antenna could be far away from a power source, such as on your roof or up a mast. It ensures DC power reaches the LNA, but at the same time does not enter the RTL-SDR dongle, as DC current on the antenna input could destroy the RTL-SDR. For best performance it is recommended to use an LNA near the antenna, especially if you have a long run of coaxial cable between the antenna and RTL-SDR.

The filter uses Low Temperature Co-fired Ceramics (LTCC) type components as opposed to the seemingly more commonly used SAW and microstrip filters. Adam writes that each type of filter has its tradeoffs, but he believes the LTCC filter is the best for this application.

Comparison between different filter types.
Comparison between different filter types.

The insertion loss of the filter in the pass band is about 2.4 dB and the filter will significantly attenuate broadcast band FM, TV stations, WiFi and 1.8 GHz+ cell phones. However, it does not do so well with 950 MHz cell towers and possible radar on 1.2-1.3 GHz as the LTCC filter is not as sharp as a SAW filter. In Adams own tests he shows that the addition of the filter improves ADS-B decoding performance by about 20%, but the improvement you see will vary greatly with your RF environment.

The filter is currently selling for 20 Euros + 5 Euros shipping (~$28 USD).

ADS-B LTCC Filter with Bias Tee
ADS-B LTCC Filter with Bias Tee

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

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, 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

Tutorial on Combining and Rebroadcasting ADS-B Feeds with ModeSMixer2

Last week we posted about how the author of the blog had written a tutorial on the use of ModeSDeco2 for decoding ADS-B with an RTL-SDR. Now the same author has continued his tutorial by writing how to use the ModeSMixer2 software to combine multiple ADS-B datastreams into a single stream. This is useful for example if you have several RTL-SDR’s at different locations receiving ADS-B data. ModeSMixer2 can also combine data even if you are using different ADS-B decoding software such as dump1090, RTL1090 or ADSB#.

The author’s tutorial goes over setting up ModeSDeco2 to broadcast data over the network, setting up ModeSMixer2 to receive data, and also setting up the basestation.sqb file to add airline logos and silhouettes to the web based GUI of ModeSMixer2.

Screenshot of the ModeSMixer2 web based GUI.
Screenshot of the ModeSMixer2 web based GUI.

Tutorial on using Modesdeco2 for ADS-B with the RTL-SDR

Over on the blog, the author has recently created a tutorial showing how to use Modesdeco which is a multi platform command line ADS-B decoding software application. ADS-B stands for Automatic Dependent Surveillance Broadcast and is a signal broadcast by aircraft that can be used to track them like a radar. 

Modesdeco is a command line ADS-B decoder quite similar in purpose to other software like dump1090, RTL1090 and ADSB#, however it has more available features built into it. The blog author writes about Modesdeco:

Want to feed BaseStation and PlanePotter at the same time? No problem. Want to add another data stream for Virtual Radar Server? No problem. Want statistics about the types of data being received? No problem. Want to run it on a variety of platforms, including Windows, Mac OS X, Linux, or the RaspberryPi? No problem.

The author’s tutorial goes over setting up the software on Windows and turning on some features like it’s web statistics interface, interactive map and how to feed data to another virtual radar application like Basestation. In the future the author plans to write a second tutorial showing how to use another feature which allows a user to combine the ADS-B feeds from various computers running Modesdeco.

Screenshot of the Modesdeco statistics web interface.
Screenshot of the Modesdeco statistics web interface.

dump978: UAT Decoder for the RTL-SDR + FlightAware App now supports UAT

In most of the world aircraft use the ADS-B standard for location tracking which transmits at a frequency of 1090 MHz. However, in the USA there is the option for aircraft to instead use the Universal Access Transceiver (UAT) protocol which transmits at 978 MHz.

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. It seems that most small aircraft in the USA prefer to use the UAT system due to it’s lower cost and additional features. 

A few months ago an experimental version of dump978 MHz was released which is what we believe to be the first working UAT decoder for the RTL-SDR. It’s still in experimental development, however the FlightAware team have already referenced it for developing their Android ADS-B app which we posted about a few days ago. Because of the work done with dump978, the beta version of the FlightAware Android app has recently been updated and can now support UAT decoding. To download the beta version with UAT you may need to sign up to their public beta. More information about the beta can be found on their Google+ beta testing community page.

FlightAware ADS-B App which now supports UAT decoding.
FlightAware ADS-B App which now supports UAT decoding.

ADSBox: New ADS-B Decoding Software for Linux

Recently Roman, a programmer and reader of wrote in to let us know about his ADSBox software which is a free opensource Linux based ADS-B decoder (page in Russian, use Google Translate) with several interesting features. ADSBox contains a decoder and a nice web interface which allows you to view flight information in a table or in Google maps, or even through a Google Earth interface. The software also automatically loads up a photo of an aircraft if you click on it in the map. Roman has actually been working on ADSBox since 2011 and seems to have recently added RTL-SDR support.

The software can be compiled on a PC with gcc, or on an embedded ARM device with arm-linux-gcc. We gave the software a quick test on an Ubuntu PC and found that it worked as expected. Install instructions are on the page linked above, but just in case here are our notes on compiling the software.

  1. Download and extract the latest version from the bottom of the page into a folder called adsbox on your Linux system. (Latest version at the time of writing: adsbox-20150409.tar.gz. Note that the Google translated download link did not work for us, use the original untranslated link if you need to)
  2. Download and extract the latest sqlite source files from (at the time of writing: into a folder called sqlite3 on the same level as the extracted adsbbox folder (not inside adsbbox folder)
  3. Edit the Makefile and set “WITH_RTLSDR = yes”. If cross-compiling for an ARM device set CC = arm-linux-gcc, otherwise leave this setting alone.
  4. Run “make”.
  5. Now you can run ADSBox with ./adsbox –rtlsdr.
  6. Go to in your browser to see and use the interface.
Screenshot of the ADSBox web interface.
Screenshot of the ADSBox web interface.

A self contained ADS-B Receiver using a Raspberry Pi and RTL-SDR

Over on the Raspberry Pi Reddit discussion board user spfoamer has posted about his Raspberry Pi + RTL-SDR based outdoor ADS-B receiver. ADS-B stands for Automatic Dependent Surveillance Broadcast and is a signal broadcast by aircraft that contains information about their locations. With a receiver like the RTL-SDR and correct software you can make an aircraft radar.

In his design the Raspberry Pi transmits location data back to a PC via an Ethernet cable. In addition the Raspberry Pi is also cleverly powered via power over Ethernet (POE) which uses unused wires in the Ethernet cable itself to carry the power. Since he uses a 12V power source, to obtain the needed 5V to power the Raspberry Pi spfoamer uses a UBEC (Universal Battery Elimination Circuit) which is an efficient device that converts voltages from up to 23V down to 5V. Additionally, he uses a 1/4 wave ground plane antenna and a 1090 MHz bandpass filter to eliminate out of band interference.

On the Pi itself he runs PiAware and contributes his data to the FlightAware network.

ADS-B with a Raspberry Pi, RTL-SDR, Bandpass Filter all powered via Ethernet cable.
ADS-B with a Raspberry Pi, RTL-SDR, Bandpass Filter all powered via Ethernet cable.
ADS-B with a Raspberry Pi, RTL-SDR, Bandpass Filter all powered via Ethernet cable.
Close up of the inside of the box.