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1090MHz - Aircraft transponder decoding using Prop? — Parallax Forums

1090MHz - Aircraft transponder decoding using Prop?

DarrenYDarrenY Posts: 61
edited 2013-05-31 05:20 in Propeller 1
Hi All,

I have been thinking about a nice new project for the prop.

I found this little device, that receives and decodes the transponder signals from aircraft:
www.zaon.aero/content/view/2/41/

As far as I can make out, it decodes the signals broadcast by the aircraft on 1090 MHz and decodes using the following signal format:
mit.edu/6.933/www/Fall2000/mode-s/signal.html

So, my question is - would it be possible to easily utilize the Prop to receive on 1090MHz and then perform the decoding, to give the location of the aircraft and other data?

I seem to remember a while back some people using the prop to transmit and recieve radio, so i'm hoping someone out there can help me here.

Comments

  • MicrocontrolledMicrocontrolled Posts: 2,461
    edited 2009-04-11 11:37
    Well.. the prop is, as you know, a digital device. This makes it difficult to receive analog signals. However, it could be done. I think you should try some objects in the object extange. You might find something there that will fit your needs. If there isn't one there, you will have to write your own object. You could try to use a decoding chip to decode the signals as well.

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    Robots are microcontroled.
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  • LeonLeon Posts: 7,620
    edited 2009-04-11 12:14
    You need a suitable radio receiver (it'll be difficult to design at 1090 MHz). The Propeller could do the decoding etc. but it isn't a receiver.

    Leon

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    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle

    Post Edited (Leon) : 4/11/2009 12:20:39 PM GMT
  • FearTurtlesFearTurtles Posts: 89
    edited 2009-04-11 12:31
    Actually it looks like transponders are digital. It sound like an interesting project. Not sure where you would find a suitable receiver though. In the end it might be cheaper to just order the receiver in your link.
  • virtuPICvirtuPIC Posts: 193
    edited 2009-04-12 08:19
    I agree to the other messages. To receive the signal you need some other hardware. Since the signals will be comparably strong I would try an antenna, maybe an amplifier, and a mixer that mixes the signal to a few MHz. Then you can use the prop to demodulate and do the timing at an accuracy of maybe 100 ns giving a spatial error of some 100 ft. The reception and demodulation probably are the most difficult task.

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    www.airspace-v.com/ggadgets for tools & toys
  • DarrenYDarrenY Posts: 61
    edited 2009-04-12 10:28
    OK, so from the sounds of your posts this sounds do-able. So i think I have found my next project! smile.gif

    As long as I can get the transponder signals decoded into 0 and 1's (ok, 0v and 3.3v...) then the actual decoding via the Prop would be implementable.

    The difficult part is going to be getting the signals decoded.

    virtuPIC you described something along these line....

    1 GHz Antenna ----> Amplifier ----> Mixer ----> Prop

    Can anyone give any pointers or know of any suitable hardware that I could use to do this?

    (I realise we are getting off topic here but please stay with me....I haven't done any RF type electronic design before!)
  • kwinnkwinn Posts: 8,697
    edited 2009-04-12 13:27
    I wonder if it would be possible to modify one of the cordless phone receivers that operate at 960MHz to receive 1090MHz?
  • LeonLeon Posts: 7,620
    edited 2009-04-12 13:35
    Get the ARRL Handbook for Radio Amateurs, and the ARRL Microwave Manual.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-04-12 18:03
    These transponders apparently reply using pulse position modulation (PPM). The pulses are only 0.8us wide, which rules out downconversion to 1MHz. I've looked at single-chip receiver ICs from Atmel, Freescale, Linear, and Micrel, but none has the bandwidth required to detect such narrow pulses. Some sort of direct-conversion receiver design may be the best solution.

    -Phil
  • Ole Man EarlOle Man Earl Posts: 262
    edited 2009-04-13 02:20
    I was one of the original 12 engineers of the TCAS (Traffic Collision Avoidance System) for commercial aircraft in the early 90's. Traffic avoidance required 2 WAY communications between transponders. The Honeywell unit cost over $250,000 per UNIT. I looked at the url and I seem skeptical. You don't just look at the transponder signals and determine altitude and distance. Altitude yes, distance no. But I am drawing from OLD school technology, maybe it's different now !
  • virtuPICvirtuPIC Posts: 193
    edited 2009-04-13 08:08
    These days you can buy a small GA TCAS receiver at a very much lower price. I don't remember if for a few hundred dollars or a few thousand dollars - affordable for SEPL plane owners anyway. And I don't think they have a transmitter. I don't know anything about their technology. I would expect they measure and somehow extract data from time differences between signal from radar station and transponder signal. We could even push this up with data on our own position and position change.

    P.S.: For non-aviators: SEPL = Single Engine Piston Land.

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    Airspace V - international hangar flying!
    www.airspace-v.com/ggadgets for tools & toys
  • DarrenYDarrenY Posts: 61
    edited 2009-04-13 09:57
    Hi All,

    These are the commercial devices I found that sparked my interest into doing my own:

    www.kinetic-avionics.co.uk/sbs-1.php
    www.airnavsystems.com/RadarBox/index.html

    They are commercial 'real-time' virtual radars that receives Mode-S/ADS-B transmissions from the aircraft, so it is possible.

    virtuPIC, yes you can buy very low cost transponders for GA (Kinetic in my link above even sell a handheld Mode-S transponder for GA and glider pilots, I think for less than $1500) and they DO contain a transmitter. The ground station transmits on 1030MHz and the airborne part replies on 1090MHz.

    Having looked around the internet and found various info sources on software defined radio I came accross GNURadio and some associated hardware.
    It seems they use a MAXIM 2118 Complete DBS Direct-Conversion Tuner IC, so i'm wondering if this could be used.
    www.maxim-ic.com/quick_view2.cfm/qv_pk/3426

    Post Edited (DarrenY) : 4/13/2009 10:19:07 AM GMT
  • LeonLeon Posts: 7,620
    edited 2009-04-13 13:32
    That chip would be useful. The Propeller isn't a very good basis for an SDR, though. It hasn't got enough memory, doesn't have DSP functions, and probably isn't fast enough. A dsPIC might be a good choice, and would be cheaper.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle

    Post Edited (Leon) : 4/13/2009 1:37:56 PM GMT
  • Carl HayesCarl Hayes Posts: 841
    edited 2009-04-13 16:37
    The transponder response (that is, the signal transmitted from the aircraft) does not include any position information. It includes only an identifying number set on thumbwheel switches by the pilot, and (optionally) an encoded altitude. The radar facility knows in which direction its antenna is pointing, and derives bearing from that; and it measures the time elapsed from the time it transmits a radar pulse to the time it receives a response, and derives distance from that. Knowing bearing, distance, and altitude, the radar facility calculates the aircraft's position. You won't have that information (except altitude), so you can't calculate a position.

    The encoded altitude, which you can read, is a pressure altitude; so you would also have to know the current altimeter setting for the surrounding area if you want to calculate the actual altitude of the aircraft.

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    · -- Carl, nn5i@arrl.net

    Post Edited (Carl Hayes) : 4/13/2009 4:42:20 PM GMT
  • DarrenYDarrenY Posts: 61
    edited 2009-04-13 16:55
    Hey Carl,

    Yep, totally agree with you - you can't get any positional info from a standard ModeA/C transponder reply. But the Mode-S and ADS-B replies are different. They DO contain lots of data, including aircraft ID, position, altitude and a host of other info.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-04-13 18:08
    Darren,

    Pursuant to the Maxim chip, what kind of experience do you have laying out printed circuit boards? Have you ever done one that has to accommodate UHF frequencies? I've never done the latter, and I suspect it's not a cakewalk, since trace lengths, impedances, and groundplanes require such careful design at these frequencies.

    -Phil
  • LeonLeon Posts: 7,620
    edited 2009-04-13 19:29
    Microwave Office is a very nice package for designing that sort of thing, but it's rather expensive.

    Leon

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    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • TJHJTJHJ Posts: 243
    edited 2009-04-14 01:09
    The link you provided is for a mode S transponder which is a new system being implemented. Currently the actually Mode S information about the plane eg position, alt, speed, ect. All comes from a ground station that is broadcasting it back to the aircraft. So You have to be in a mode S enabled area in order to receive this information. The TCAS (Traffic Collision avoidance system) you show is actually a mode C receiver. Mode C only transmits a ping back when it receives the ask code. Knowing the time from when it was sent gets you distance and heading, see Carl's post above. In the return code the altitude can or can not be encoded and is required depending on operating area.

    If you are in a mode S area(Near me, San Fran, Los Angles, Seattle, Vegas look up class B airspace, last I heard all class B are S mode equipped outside of that its hit or miss. ) it would be interesting to decode all the flight data coming back, but it would get pretty complex because the return is directed to A aircraft and only tells of so many planes near by. To see the whole picture you would have to figure out which plane it was sent to, and which plane that is in reference to all the other aircraft so you dont mark it 2x-xxx times.

    Now how the Zaon MRX works. It is looking for the same request signal that all the other transponders are looking for. It then waits and looks for a signal received back from another transponder in the area. Time from the first request to send, and the received signal gives distance from the aircraft. It can not generate its own request to send signal. You could but I dont think the FAA or FCC would be to happy about it.

    That particular unit the MRX does not have a data output. The next model up the PCAS that can determine range and direction and heading using a combination of doppler effect and some neat tricks. Has an Rs 232 com in it. Now figuring out the standard and what is actually in the data is on my to do list, if someone wants to take it up please do. Its pretty far down the list.

    Either way their claimed range is about 5 mi, in my practical experience with the PCAS its about 2-3 mi. Outside of that it says the plane is all over the place.

    Now interesting idea, if you know the location of the airport transmitter. You could find its distance and bearing to you, Find the sync time from when the signal hits you. Knowing that all returns could be solved for location and bearing from you. Kinda confusing idea, If anyone wants a better explanation on how to do this I will.

    TJ

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    I owe everyone here a bunch, So thanks again for answering my dumb questions.
    Projects. RG500 ECU system. PropCopter. Prop CanSat. Prop Paste Gun.
    Suzuki RG500 in a RGV 250 frame.
    Bimota V-Due (Running on the fuel injection system)
    Aprilia RS250
  • Carl HayesCarl Hayes Posts: 841
    edited 2009-04-14 04:12
    TJHJ said...

    Now interesting idea, if you know the location of the airport transmitter. You could find its distance and bearing to you, Find the sync time from when the signal hits you. Knowing that all returns could be solved for location and bearing from you. Kinda confusing idea, If anyone wants a better explanation on how to do this I will.
    Hmmm --

    In that case, you have the time it takes for signals to traverse two legs (from the inquiring radar to the aircraft, and from the aircraft to you; but you don't know the time for either leg by itself.· This is sufficient to establish an ellipse -- the aircraft is somewhere on that ellipse -- but not enough to establish a single point.· The two foci of the ellipse, by the way, will be the radar, and you.

    Stick two pins in a board (they will be the foci).· Make a loop of string.· Tie a pencil somewhere on the string.· Pass the string around the two pins (foci).· Keeping the string taut, you will find that you can draw an ellipse.·

    One pin is the radar.· The other pin is you.· The aircraft is the pencil.·

    The string always forms a triangle with its vertices at the two pins and the pencil.· One of these is of constant length (between the two pins).· The other two vary, but their sum is known, just as the total distance from the radar to the aircraft and then to you is known.· But you don't know where on the ellipse the aircraft actually is.

    Bummer.

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    · -- Carl, nn5i@arrl.net
  • TJHJTJHJ Posts: 243
    edited 2009-04-14 15:23
    But you know the angle that the 1st signal was sent from. The transmitter stations are narrow beam( I cant think of the technical word for it). That is why they rotate. Most rotating "Radar arrays" you see at airports are in fact only transmitter/ reciever arrays for the transponders. So thats what I was describing with the sync singal, knowing its intial bearing to you. And its rotation time from time between ping signals. As a general flying rule, only miltary airports have true radar, for full vector to final IFR stuff.

    So look at the attachment, we know our distance and time the signal will take to get to us. When in the arc the signal was sent. So for simplicty not doing the time calculation.

    Law of sins gets us the angle a

    A/sin(a)= B/sin(b)

    a = sin-1(B/(A*sin(b)))

    Law of cos can gives us the solution for the aircrafts current distance.

    A² = B² + C² − 2BC cos·(a)

    The time sent versus time recived calc gets kinda nasty, but I think I have this correct. I have to look up the travel time for a radio signal to solve the rest of it.



    TJ






    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    I owe everyone here a bunch, So thanks again for answering my dumb questions.
    Projects. RG500 ECU system. PropCopter. Prop CanSat. Prop Paste Gun.
    Suzuki RG500 in a RGV 250 frame.
    Bimota V-Due (Running on the fuel injection system)
    Aprilia RS250

    Post Edited (TJHJ) : 4/14/2009 3:28:41 PM GMT
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    aircraft transponder.bmp
    750K
  • Carl HayesCarl Hayes Posts: 841
    edited 2009-04-14 19:00
    TJHJ, as nearly as you seem willing to be understood, I'm sure you believe whatever it is·you're trying to say.

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    · -- Carl, nn5i@arrl.net
  • DarrenYDarrenY Posts: 61
    edited 2009-04-14 19:08
    This is what I love forums for - lively discussion wink.gif

    OK, a little more info on the two commercial devices I mentioned earlier.

    Both products have specialized single-use receivers in them. Unlike most radios there is no Intermediate Frequency (IF). The ADS-B data flows from the supplied antenna through an LNA pre-amp. It is bandwidth filtered, and then the pulses are extracted using a logarithmic amplifier chip. This chip can operate directly at the ADS-B frequency of 1090 MHz. These analog pulses are then applied to a high speed analog to digital (A/D) converter (40 MHz for Kinetic, 8 MHz for AirNav) and then on to whatever micro controller (in these cases both use an FPGA)

    Also, this is a little gem of a site:
    www.tech-software.net/
  • BazmundiBazmundi Posts: 3
    edited 2013-05-31 05:20
    Sorry chaps. My research tells me you need a 64-bit linux box running GNURadio to do the job, along with $20 tv tuner would you believe (http://www.irrational.net/2012/08/06/tracking-planes-for-20-or-less/) alternatively you can build a complete front end (replace the atmega with a prop) (http://www.lll.lu/~edward/edward/adsb/SimpleAdsbReceiver.html).
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