ADS-B.
What is ADS-B?
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).
How does it work?
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.
Receivers
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 Data and the Display
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.
Improving Reception
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.
An example of how an ADS-B
receiver can assist with predicting AEP
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!
Conclusion
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!
Useful Links
·
http://www.kinetic-avionics.co.uk/
·
http://www.aircrafttrackingavionics.com.au/
·
http://www.airnavsystems.com/RadarBox/index.html
·
http://www.airservicesaustralia.com/projectsservices/projects/adsb/default.asp
·
http://www.flightradar24.com/
·
http://www.coaa.co.uk/planeplotter.htm
·
http://www.vk3hz.net/radiosites/PP_and_RSD.html
Updated
25/1/2011