May 2006

Welcome back to the satellite pages after a break of a few months. I have been away backpacking through the Middle East and saw some amazing sights, some even satellite related which will be presented in coming issues of the magazine.

There is a lot more to satellite monitoring than just watching television from around the world, and this month we take a break from the usual television news to have a look at monitoring air traffic (in Australia) via both satellite and microwave.


ATC circuits on Optus B1

Optus B1 is a KU band satellite positioned above the equator at 160 degrees east. Optus B1 is best known for it's use as the primary satellite for Australian outside broadcast and raw studio feeds. Optus B1 is also the satellite that is used by SBS and the ABC to feed their terrestrial transmitters with programming around Australia. However there are many other services available from Optus B1, one being Air Traffic Control (ATC) channels covering flights all across Australia.

You will find the ATC on the horizontally polarised beam and it is dead easy to tune into the signals using a regular UHF radio scanner connected to a suitable dish. ATC channels are found as Narrow Band FM signals between 980.000 MHz and 1015.000 MHz (when using an LNB with a 11.300 LO output frequency). Channels include en-route, approach, ATIS (Automatic Terminal Information Service), VOLMET (Weather broadcasts), chat between controllers regarding traffic handoff as well as relays of the HF frequencies used when aircraft are flying across the Pacific & Indian oceans etc. ATC for all of Australia is heard, there are literary hundreds of channels.

I have set up a dedicated dish for ATC monitoring at my shack with a PLL LNB/Feed connected to an 18 Volt power supply, the coax cable then directly feeds my scanner. If you already have a satellite TV receiver on Optus B1 it's very easy to connect a scanner to your dish! On the back of most receivers there is an LNB out port (sometimes called loop through) you connect a coax cable from here to your scanner. Using your receiver tune up any Optus B1 Hz television channel and then move across to the scanner. Now tune between 980.000 MHZ and 1015.000 MHz and you will find the signals. You may wish to use a non-power pass splitter, to protect your scanner input from the 18V on the coax that is used to power the LNB. Most receivers don't pass the LNB power voltage through the LNB out loop through port, however if your not too sure about your receiver, a non-power pass splitter will ensure you don't damage your scanner front end.

On Satdirectory's support page you can request a copy of a Microsoft Excel spreadsheet file which lists ATC frequencies on both Optus B1 & B3 with notes on what I have monitored on each channel. When looking at my log you will find both "Night" and "Day" frequencies listed. This has nothing to do with the satellite transmitting frequency (as far as I know) but more to do with my LNB drifting as the air temperature changes. Almost certainly you will find that the frequencies on your system are different to my log. The LNBs we use to watch sat TV were not designed for this narrow band FM work, and so they will drift and also give a slightly different frequency output dependent on model & brand.
 
When first using the spreadsheet I would recommend you tune up an ATIS frequency - for example Hamilton Island on Optus B1 990.770MHz. This frequency gives a continuous report of conditions at the Hamilton Island Airfield (ATIS = Automatic Terminal Information Service). Can you hear it on 990.770? Chances are you can't due to differences between my LNB and yours, so tune slightly up and down the band till you find it. Once you have found the ATIS you can add a column to the spreadsheet with "your" frequency. Calculate the difference between the frequency where I hear the ATIS and where you have heard it and then you can apply the correction factor to each frequency in the spreadsheet.


 
Virtual "radar" of civil airspace

Monitoring air traffic control is a particular passion of mine! What has really added a new dimension to my interest is the reception and decoding of aircraft Secondary Surveillance Radar ADS-B mode signals on 1090 MHz. ADS-B is a signal that gets modulated on top of an aircraft's transponder Mode S signal. Providing more information than the bare transponder, the ADS-B signal includes data that allows the decoding of the aircraft's position in latitude and longitude, altitude, heading and vertical speed. Also reported is the aircraft's flight number  and the airplane's unique identifier, which in turn enables suitable software to figure out the airplane type, owner and registration from a database.

Most international airlines that have aircraft in their fleet that regularly fly into the US or Europe have their planes equipped with ADS-B. These aircraft are easily received with a suitable receiver and software program when they are in range of your antenna (up to 250 nautical miles). The majority of Jetstar and Virgin Blue aircraft transmit ADS-B signals, however at this stage only the newer aircraft in the Qantas fleet (737-800's and Airbus A330's) can be tracked. ADS-B will become mandatory addition to both general aviation and airline operated aircraft probably around 2009, so as time goes on the volume of traffic displayed will increase.

To give you an idea of a typical ADS-B virtual radar display that you can display with real-time data examine the captured a screenshot on this page. Jetstar A320 VH-VQK is on final to runway 16 Right at Sydney. The "data tag" on the aircraft advises that the aircraft is Jetstar Flight 623 coming in from Maroochydore. At the time I took the screenshot the aircraft's speed was 119 knots (ground speed) and at 650 feet (based on standard QNH). Virgin Blue Flight 559 is north-east of Mudgee while a China Southern Airbus A330-200 is climbing through 19,000 feet and just about to pass over the Richmond Airforce Base.

To sample an example of a typical ADS-B display have a look at Balthasar Indermuehle's excellent real-time stream of air traffic over Sydney.


MediaExplorer

To close off the month just a reminder that the "MediaExplorer" DVDs remain available at a special member price available through the club's publications store. By purchasing MediaExplorer through the club you will receive almost 50% off the regular bookshop retail price. MediaExplorer is a full multimedia catalogue of free-to-air signals available from major regional satellites to backyards in Australia and New Zealand. With six DVD video disks and the companion DVD-ROM content, MediaExplorer features over eleven hours of world television and fourteen hours of radio from hundreds of broadcasters around the planet. It's the equivalent of both the "World Radio TV Handbook" and the "Passport" book for satellite dish users. Even if you don't intend to put up a dish it's a great way to glimpse into what the whole digital satellite revolution is about. Further details on MediaExplorer can be found at www.mediaexplorer.org
Phased-Locked-Loop (PLL) LNB for monitoring ATC on Optus B1
90cm offset dish for monitoring ATC on Optus B1
Virtual Sydney "radar" display produced by using ADS-B data on 1090 MHz
1090 MHz antenna for receiving ADS-B data direct from aircraft
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