Automatic Dependent Surveillance – Broadcast, or ADS-B, is a “Co-operative surveillance technique for Air Traffic Control”. Put simply, aircraft are equipped to automatically state who they are, where they are and what they are doing!
ADS-B can provide exceedingly useful data for an amateur radio enthusiast exploring Aircraft Enhanced Propagation (AEP).
Aircraft are fitted with an electronic device called an ADS-B transponder. The transponder transmits Data Packets “every second or so” (Airservices Australia) at a frequency of 1090 MHz. These packets are picked up by a dedicated receiver, which interfaces with a personal computer. The associated software then uses the information contained in the packets to create a virtual RADAR screen display.
All new commercial aircraft are supplied with an ADS-B transponder as standard equipment. Older aircraft will be retrofitted with transponders.
At the time of writing two commercially built receivers were available. One, produced by an American company called Airnav, is the Radar Box. The other, manufactured by the British company Kinetic Avionics, is called the SBS-1.
The Airnav Radar Box is available via online order on the Airnav website (see Useful Links). The associated software, sold separately to the receiver, is also available for purchase on the Airnav site.
The Kinetic Avionics SBS-1 is available through the Australian distributor, Aircraft Tracking Avionics, Vermont, Victoria (see Useful Links). The receiver comes with the associated software (a programme called “Base Station”), a small 3-dBd magnetic-mount whip antenna, and a USB cable.
Kinetic Avionics SBS-1
The receiver I chose is the Kinetic Avionics SBS-1, and the following description of the Data and the Display is based on this receiver and the associated Base Station software.
Data files that can be preinstalled with the software will provide:
· Map Outlines – outlines of the landmass, and State boundaries;
· Aircraft Tracks – the established routes that the aircraft (nominally) follow;
· Waypoints – navigational marker points along a route;
· Airport Markers – locations of airports;
· Latitude/Longitude Grid – lines of Latitude and Longitude, at 1° intervals.
Base Station display, with Map Outline, Aircraft Track, Waypoints, Aircraft Markers and Lat/Long Grid.
Data contained in the packet will provide:
· Hex Address – a n-character address unique to each aircraft;
· Callsign (Flight ID) – associated with whichever flight the aircraft is undertaking;
· Altitude – the height above sea level of the aircraft, configurable to either feet or metres;
· Bearing – the direction in degrees (True, not Magnetic) the plane is flying;
· Airspeed – speed, in Knots, of the aircraft;
Base Station display, with selected aircraft showing Hex Address, Callsign, Altitude, Bearing, Airspeed and location with respect to SBS-1 Receiver location.
Base Station can overlay Radial Distance Rings, which are adjustable in diameter. It can also overlay a line between a selected aircraft and your location, showing the distance & bearing (Degrees True, not Magnetic) of the aircraft from the receiver location.
The SBS-1 can be networked to Virtual Air Traffic Control websites such as “OpenATC”, which in turn can overlay the data in Google Earth.
As mentioned earlier, the SBS-1 comes with a 3-dBd magnetic-mount whip, about which there are some impressive, if vague claims on the Kinetic SBS-1 Users Forum site regarding the reception footprint – supposedly up to 250 miles (whether this is Imperial Miles or the aviation standard Nautical Miles is not made clear). The UK is surrounded by a large amount of fairly flat water – perhaps that explains things! There is a better evaluation of what can be expected shown in a table on the Aircraft Tracking Avionics website, in the Antenna Accessories page.
In the spirit of Amateur Radio (well, one of the spirits) I decided I needed a bigger antenna, with more gain. I constructed a 16-element coaxial Co-linear (~12-dBd?), and mounted it 3 metres above the top of my 144 MHz array – about 14.5 metres above ground level. After a short (3.5 metre) run of SCF12-50 heliax, a VK5EME kit dual-stage Pre-amplifier (MGF1302 followed by an ERA-1) provides a boost before the signal hits the run of LDF4-50 to the receiver.
Maximum range observed reliably so far is 225 nm (416.7km), with aircraft flying at high altitude (38,000-40,000 feet), though instances of greater distance have been observed as we enter late spring and come under the influence of Tropospheric “ducting”.
I decided that wasn’t enough, so I built a 28-element T-boom Yagi. This has a calculated gain of 16.7-dBd. Admittedly I lose the omni-directionality of the co-linear, but I was more interested in maximising my forward view. This is, after all, where I’d be transmitting to and receiving from, when using Aircraft Enhancement.
Aircraft have now been seen out to 260 nm, at least in my most favourable direction (i.e. flattest horizon).
Base Station display; Malaysian Airlines flight 123 en route to Sydney – 259.4 nm from the receiver.
Aircraft Enhanced Propagation relies on an aircraft being mutually visible to the two amateur stations wishing to establish a contact. Obviously knowing where the aircraft is will greatly simplify the process of establishing a contact! There is little point in calling in anticipation of an AEP contact, if there are no aircraft in the vicinity of the enhancement area; on the other hand, monitoring the position of an aircraft as it approaches an enhancement point can trigger calling and/or listening. The propagation mode of an unexpected contact can be narrowed down or identified if the virtual RADAR display shows an aircraft in a favourable position.
The duration of an AEP “opening” is defined by several factors, including:
· Aircraft airspeed,
· The angle of incidence between the aircraft track and the signal path between the two stations,
· Size of the aircraft,
· Gain and beamwidth of the station antenna,
· Distance between the two stations,
· Frequency of operation, and
· Height of the aircraft.
The affect of aircraft height on signal strength at 432 MHz and 1296 MHz, over the path between VK1 and my QTH, is something I can now start to collect data on using my ADS-B receiver.
I recently made observations involving flights from Sydney to Perth, which caused enhancement to the VK3RRU Mildura and VK5VF Adelaide 144 MHz beacons. The results ably demonstrate both how useful the ADS-B data can be to those chasing AEP, and how small the window of opportunity can be with an AEP “opening”.
Base Station display – QFA 565.
The aircraft involved in the detailed observation was QANTAS flight QFA 565, and it became visible to my receiver as it flew over Culcairn, NSW. It had a bearing of 263 degrees (True) as it flew towards the Bordertown waypoint, where it would change course before heading out over the Coorong and the ocean. The track is designated J142 on ERC H3 (air traffic chart, High #3).
VK3RRU is at 388 km and 328 degrees from my QTH; VK5VF is at 571 km and 294 degrees. I listened, firstly for VK3RRU then VK5VF, over the next 25 minutes, and my observations were as follows:
2246:50z: QF565 due north of VK3BJM
2248:48z: QF565 @ 350° - VK3RRU 319 (troposcatter level)
2250:50z: QF565 @ 340° - VK3RRU 319
2251:45z: QF565 @ 335° - VK3RRU rest period (no key-down tail).
2252:20z: QF565 @ 333° - VK3RRU 319 with fast flutter.
2253:00z: QF565 @ 330° - VK3RRU rest period.
2253:30z: QF565 @ 328° - VK3RRU 539
2254:10z: QF565 @ 325° - VK3RRU 419
2254:50z: QF565 @ 324° - VK3RRU 319 with fast flutter.
2255:20z: QF565 @ 321° - VK3RRU 319 with fast flutter.
2256:10z: QF565 @ 320° - Temporarily lost radar visibility of aircraft. At this time I shifted the 2m array, and receiver, from VK3RRU to VK5VF.
2256:35z: QF565 @ 316° - Aircraft reappeared.
2257:40z: QF565 @ 314° - Temporarily lost radar visibility of aircraft.
2258:35z: QF565 @ 310° - Aircraft reappeared. Still nil signals audible from VK5VF.
2300:35z: QF565 @ 304° - Still nil signal audible from VK5VF.
2302:00z: QF565 @ 304° - Temporarily lost radar visibility of aircraft (location 36.208 S, 142.547 E - again, close to Warracknabeal). Still nil signal audible from VK5VF.
2304:40z: QF565 @ 296° - Aircraft reappeared briefly - marginal signal with position update before data froze.
2305:00z: QF565 @ 296° - VK5VF 419 with fast flutter.
2305:25z: QF565 @ 296° - Lost radar visibility of aircraft. VK5VF 419 without flutter.
2307:00z VK5VF faded into the noise floor.
The aircraft are about 150 km from my QTH when they cross the VK3RRU beam heading - very close to halfway to VK3RRU. The aircraft are 250 km from my QTH when they cross the VK5VF beam heading – they are 320 km from the Mt Lofty site. This scenario has been observed on three further occasions. Typically the aircraft have been logged as flying at altitudes between 38,000 & 40,025 feet.
Even when an aircraft is “lost” to the receiver, the airspeed data can be used to quite accurately predict when enhancement should be expected if the aircraft track intersects with a beam heading.
Networking the ADS-B data.
It is possible to upload the positional data from your ADS-B receiver to a server, which can then make it available to anyone with Internet access.
FlightRadar24 is one such web server/viewer. An email to their website, with a few details about your location, will result in a personalised file being sent to you. When this is run at the same time as your ADS-B receiver being on, data is uploaded to the FlightRadar24 site, and is viewable by anyone. It is overlaid on Google Maps. FlightRadar24 also have an iPhone “app”, so you can view the data on your phone, too!
My data feed is known on FlightRadar24 as “YKTN”.
A screen dump, from FlightRadar.com, shows Tiger Airways flight 5204 en route to Brisbane.
Similarly, PlanePlotter is a programme that runs on your computer, and shares data with other PlanePlotter users. The basic map supplied with PlanePlotter is, well, very basic; but the data can be overlaid elsewhere…
A screen dump, from PlanePlotter, shows numerous aircraft over SE Australia.
David, VK3HZ, has set-up his “Radio Site Display” so that the necessary Google Earth data files can be downloaded to your computer to show both locations and directions to other amateurs, beacons and portable operating site (the data is extracted from VK Logger), and the positional data from PlanePlotter.
A screen dump, from Google Earth with RSD running, shows numerous aircraft over SE Australia, along with the designated aircraft routes.
Another screen dump, with the addition of a 144 and 432 MHz propagation beacon overlay.
A closer view, this time with beam headings to VKs 2DO, 1DO, 1BG and 1ZQR overlaid. TGW6208 is visible crossed the beam heading to VK1DO at Carwoola – and large amounts of AEP result from this!
AEP openings, especially those over paths nearing the physical distance limit as defined by the height of the aircraft, can be brief in duration. The likelihood of success over such paths is increased with the amount of accurate and up-to-date information available to the protagonists, and an ADS-B receiver provides this by the bucket!