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Improved ADS-B reception on a computer Three new products give you much-improved reception of ADS-B signals from aircraft on your computer, allowing you to track most nearby flights. After reviewing them, we’ll also give you some tips regarding the best ADS-B reception software. by JIM ROWE B ack in the August 2013 issue of SILICON CHIP, we published a couple of articles on receiving ADS-B signals broadcast from aircraft. The first article (“ADS-B & flightradar24.com”) provided an introduction to ADS-B – where it came from, what it is and how it works; see siliconchip.com.au/Article/4204 The second article (“Track Aircraft On Your Own ADS-B Receiving Station”; siliconchip.com.au/ Article/4209) explained how you could make your own low-cost setup for receiving ADS-B signals using a computer and a low-cost USB DVBT dongle. Since then, improved USB dongles have appeared, offering significantly better performance for SDR (software defined radio) reception (like ADS-B) compared with first-generation DVBT dongles. 32 Silicon Chip Also, some of the ADS-B receiving software available in 2013 is no longer available – specifically, freeware programs like ADSB# and ADSBScope. But new software has appeared to take their place. Some of the earlier non-freeware software has also been improved and is still not overly expensive. Since so much has changed recently, we tried out three new products aimed at providing improved ADSB reception for your computer, and (Above): the FlightAware 1090MHz bandbass filter, which significantly improves ADS-B reception by attenuating unwanted signals outside the ADS-B band. (Opposite): the ProStick Plus, a USB dongle specifically intended for optimum ADS-B reception. Australia’s electronics magazine siliconchip.com.au we’ll describe what we found. But before that, let’s quickly go back over the concept of ADS-B, in case you haven’t read the August 2013 articles. ADS-B stands for “Automatic Dependent Surveillance – Broadcast”, an aircraft information and identification system. Most modern aircraft are fitted with a high-integrity GPS receiver, which continuously monitors their exact position (latitude and longitude). They also have a suite of equipment which monitors their barometric and geometric altitudes, the rate of climb or descent, the tracking angle (heading) and their ground speed. They are also fitted with a Mode-S transponder which takes all of this information (together with the aircraft’s unique ICAO 24-bit Aircraft Address and Flight Identification) and broadcasts it automatically as a 120-bit ADS-B digital ‘squitter’ at 1090MHz, twice per second. These ADS-B squitters can be received by ground stations and other aircraft; many large aircraft are able to receive the ADS-B signals as well, so their pilots can be fully aware of other aircraft in their vicinity. As we explained in the 2013 articles, it’s quite easy to receive these ADS-B signals via a low-cost SDR using your computer and a USB dongle capable of reception at 1090MHz, a suitable omnidirectional UHF antenna and appropriate software. I measured the insertion loss of the FlightAware 1090MHz bandpass filter at a commendable 1.92dB (its specs say 2.5dB!). Other measurements revealed a bandwidth of 1015-1140MHz and an attenuation of around -35dB at 960MHz and 1210MHz. New gear The FlightAware ADS-B 1090MHz bandpass filter is designed to improve ADS-B reception quality by attenuat- After we published the article in the May 2020 issue reviewing the siliconchip.com.au new RTL-SDR Blog V3 USB-linked dongle (which we found an excellent performer; see siliconchip.com. au/Article/14429), we were contacted by the local agents South Eastern Communications. They told us about three products are specifically designed for high-performance ADS-B reception, all from a company in Houston, Texas called FlightAware: • a low insertion loss 1090MHz bandpass line filter; • an omnidirectional antenna specifically designed for 1090MHz ADSB reception; • and a new dedicated ADS-B dongle called the ProStick Plus. All three are made in Taiwan. We evalulated the 1090MHz bandpass line filter first. The ADS-B line filter Australia’s electronics magazine ing signals outside a 15MHz frequency band centred on 1090MHz. This makes it very suitable for use with an RTL-SDR dongle, as most of these are wideband devices and lack any front-end tuning. So they can have difficulty rejecting strong interfering signals close to 1090MHz. The FlightAware filter is a passive unit and very compact, measuring only 56mm in length (or 78mm overall, including the input and output connectors), with a diameter of 19.5mm. It is fitted with an SMA plug at one end (to connect to the antenna) and an SMA socket at the other end, to connect to the input of your dongle. The rated bandwidth is 9801150MHz, with an impedance of 50Ω and an insertion loss of less than 2.5dB. Its cost is quite modest, at $40.00 plus postage. I measured the filter response using my Signal Hound USB-SA44B spectrum analyser and USB-TG44A tracking generator, together with the Spike software. The result is shown above, which indicates that the filter’s performance is impressive. It has a measured insertion loss of only 1.92dB at 1090MHz, a bandwidth of 1015-1140MHz and an attenuation of around -35dB at 960MHz and 1210MHz. So it should significantly improve the ability of a ‘standard’ SDR to receive ADS-B signals, by reducing interference from signals outside this band. October 2020  33 Even at the height of the COVID-19 lockdown, there was significant aircraft movement around Sydney, as shown here on my computer screen grab. The near-solid red “blob” marks the many aircraft on the ground at Sydney airport. Zooming in will separate these into individual aircraft IDs. To confirm that this would improve the ability of any ‘standard’ SDR to receive ADS-B signals, I connected the filter between my RTL-SDR Blog V3 dongle and an external discone antenna, and fired up the RTL1090 ADS-B decoding software and the Planeplotter graphical plotting software on Windows 10. And despite the modest aircraft activity during the COVID-19 pandemic, the setup was able to detect, decode and plot ADS-B squitters from every aircraft in the air within a radius of at least 150km – plus quite a few parked on the ground at Sydney Airport, just a few kilometres away. I also tried the same setup without the FlightAware filter, and the results were not nearly as good. So this filter can definitely make a worthwhile improvement in your ADS-B reception, if you are using a standard wideband RTL-SDR like the Blog V3. The FlightAware 1090MHz antenna Next, I tested the FlightAware 1090MHz antenna. This is a compact little unit, housed in a cylindrical plastic tube 550mm long and 20mm in diameter, with a weatherproof cap at the top. It has a cylindrical metal base 100mm long and 25mm in diameter at the bottom, ending in a female N-type connector for attaching the feeder cable. It’s solidly made and comes complete with a cylindrical mounting bracket, two U-bolts and a full set of washers and nuts to mount the antenna atop a 25mm vertical mast. The antenna is claimed to be fully omnidirectional and to have a gain of +5dBi average. When mounted at a suitably high point without obstructions, it is claimed to be able to receive ADS-B data from aircraft up to 400km away. The antenna’s internal construction seems to be a sleeved dipole with a loaded whip above it. This combination gives higher gain relative to other omnidirectional antennas, plus a flattened response which makes it especially suited for receiving ADSB signals from aircraft at a distance. It is currently available from South Eastern Communications for $99.00 plus postage. I mounted it on the top of the mast for a UHF TV antenna, as shown in the photo, at almost the same height above ground as my discone antenna, and with a very similar ‘view’ in most directions. I hooked it up to the combination of the FlightAware 1090MHz inline filter plus RTL-SDR Blog V3 dongle, as before plugged into a laptop running the RTL1090 ADS-B decoding software feeding Planeplotter. The results were quite impressive, as you can see from the screen grab above. The FlightAware antenna delivered at least as many clean ADS-B signals as the discone, if not more. Note that although the screen grab only covers the greater Sydney area, I also expanded the coverage to include an area extending up to Newcastle and down to Wollongong. I could then see aircraft somewhat further away. So although I didn’t carry out any fancy technical tests on the antenna, my impression is that it performs at Current ADS-B software Things have changed in the last seven years when it comes to freeware and low cost software for receiving ADS-B signals using a USB dongle and your PC. For example, ADSB# (ADSBSharp) is no longer available, while ADSBScope still is, but without the ability to cope with locations “down under”. Luckily RTL1090 is still available, although from a different website from the one we gave in the August 2013 articles (see the list of useful links). And it’s still freeware. PlaneSpotter is also still available, although its name has been changed to PlanePlotter. The latest version (V6.4.6.2) is not freeware, though. You can download it for a 21-day free trial, but after that you need to pay for a licence, which costs AU$49.23 including GST. Since it also makes use of Google maps, you have to make a separate payment of AU$20 for every 1000 maps downloaded. After trying out a few of the software packages currently avail34 Silicon Chip able, I settled on using the combination of RTL1090 for the decoding and PlanePlotter for the display. They work well together, and it’s fairly easy to get RTL1090 communicating with either an RTLSDR Blog V3 dongle or the FlightAware Prostick Plus. Both of the applications will run happily with Windows 7, 8 or 10. The easiest way to install RTL1090 is by downloading the rtl1090imu.zip file, unzipping it and then running it as Administrator. Note that you can’t install it in the usual “C:\Program Files\” subdirectory though, as it writes to files in its installation directory. So you have to install it somewhere that you have write access. RTL1090-IMU is an installer and maintenance utility, which automatically downloads all of the components needed to get RTL1090 working. That includes Zadig, the driver installing program needed for Windows applications like RTL1090 to communicate with USB devices like RTL-SDR dongles. It even includes a step-by-step tutorial to help you use Zadig to install the correct driver. Australia’s electronics magazine siliconchip.com.au Useful ADS-B links • https://en.wikipedia.org/wiki/ADS-B • https://flightaware.com/ • www.flightradar24.com • www.rtl-sdr.com/ • www.rtl-sdr.com/adsb-aircraft-radar-with-rtl-sdr/ • www.rtl-sdr.com/review-flightaware-ads-b-antenna-and-filter • https://rtl1090.com/ • https://rtl1090.com/installation-manual-2/ • www.coaa.co.uk/planeplotter.htm • http://planeplotter.pbworks.com/w/page/17117302/FrontPage (Inset above): the ADS-B (1090MHz) receiving antenna and its mounting hardware . . . shown here mounted above a UHF TV antenna. Keep them more than a wavelength apart (~250mm <at> 1090MHz) and they shouldn’t affect each other. least as well as the more expensive discone, and probably better. The FlightAware ProStick Plus dongle The ProStick Plus USB dongle is an RTL-SDR dongle specifically designed for optimum ADS-B reception. At 70 x 32 x 13mm, it is almost exactly the same size as a modern RTL-SDR dongle like the Blog V3 we reviewed in May 2020. It has a female SMA input connector at one end and the usual type-A USB plug at the other. The Prostick Plus comes in a moulded plastic case rather than the extruded metal case of the Blog V3. siliconchip.com.au So superficially, it has less shielding, although there may be shielding foil inside the case (it wasn’t clear how to open the case without damaging it). Inside that case there’s more than the usual combination of a Rafael Micro R820T2 programmable tuner chip driving a Realtek RTL2832U COFDM digital demodulator chip. You also get a built-in 1090MHz bandpass filter at the input, plus an RF amplifier delivering a rated gain of +19dB with a noise figure of 0.4dB. The inbuilt 1090MHz bandpass filter has a passband covering 10751105MHz (ie, 1090±15MHz), with a rated insertion loss of 2.3dB and Australia’s electronics magazine around 30dB of attenuation outside this range. So together, the filter and amplifier combination provides an effective gain of around 16.5dB inside the passband centred on 1090MHz, plus a high degree of rejection outside that band. That should make the Prostick Plus very well suited for ADS-B reception, especially in noisy urban areas. And it’s just $45.00 plus postage, from South Eastern Communications – not much more than the RTL-SDR Blog V3 (for which they charge $35.00 plus postage). I tried out the Prostick Plus with both my existing discone antenna and the new FlightAware 1090MHz omni antenna, using as before the RTL1090 decoding program linked to the Planeplotter program. With the Prostick Plus, there’s no need to use the external bandpass filter, since it has its own built-in filter. The results were very impressive with both antennas. An example is shown in the screen on page 32. As well as showing the ‘pile’ of aircraft parked on the ground at Sydney airport, you can clearly see two aircraft flying away from Sydney out over the water, plus about eight others flying in various directions over the greater Sydney area – and one on the ground at Bankstown airfield, around 20km away! So to summarise, the FlightAware Prostick Plus dongle seems to be topof-the-line for ADS-B reception using your PC. Whether you use it with FlightAware’s own 1090MHz omnidirectional antenna or a discone antenna, itis hard to see how you could get better performance. But if you already have an RTL-SDR dongle like the Blog V3, you should be able to get almost the same results simply by getting one of the FlightAware 1090MHz bandpass filters to remove most of the EMI picked up by your antenna. These products can probably all be found on the internet, at marketplaces like eBay and Amazon. But if you’d prefer to get them from a reliable Aussie source, we can recommend South Eastern Communications. You’ll find them on the web at www.secomms.com.au, but you can also contact them by email at sales<at> secomms.com.au, or by phone to 1300 382 385 or 0434 720 006. Or if you wish, by “snail mail” to PO Box 251, McCrae, Victoria 3938. SC October 2020  35