• Category Archives Computers
  • Thermal drift issues

    The feedhorn / down converter on the dish has a pretty bad thermal drift issue. The output frequency is just not stable. It wanders around all over the place.
    We have tried to settle it down by insulating it like thus;

    It helps, but eh, its not the best way to do it as it does run hot, but it chops off about 10 Deg C of drift.
    I think long term I might need some active temperature control, but that is only going to help so much. I think I need to see about a different feed horn.
    Very disappointed.

  • C-Band ADSB

    When you write it down, in one sentence, its really very simple;
    6′ dish -> PLL LNA -> 18v DC pass-through PSU -> RTL-SDR -> SDR# -> Jaero -> VRS.
    And with that signal path, you will have planes on a map. 100+ planes from half the planet. Easy right. Ah. It could be, but if you are reading this, you probably have hit some snags.
    Also, if you are reading this, you probably have an idea of what you are trying to do, so I will skip the intro and go straight to how I did it.
    And just to be clear, we are talking about ADS-C, not ADSB, but it looks so similar that many (me included) often get it mixed up.

    You can (apparently) get by with a 4 foot dish, but I did not want to be scrapping around in the noise, so opted for a 6 foot dish, the wife was not so excited, so we both compromised and went for a 5 foot dish. If I was going to do it again, I would go a 6 to 9 foot dish, anything bigger and the pointing accuracy is going to be a ‘problem’ and not worth the extra signal strength.

    The LNB (feed-horn) matters. You want something with low frequency drift, something that is temperature stabilized would help as well. If you find something that fits the bill, let me know.
    I was recommended this one; https://www.amazon.com/gp/product/B00HVM08JI
    Having nothing to compare it with makes it a bit hard, but the short of it is that its not really stable enough. The drift will put the signal out of range of the bandwidth every hour or so. You will be chasing the signal over a few hours. Okay for testing, but no fun for something that you just want to leave running unattended (which is my plan).
    The LNB has two voltages, 13 for one polarization, 18 for the other (horizontal and vertical for example). I did not have 13 on hand, so went with 21. A little on the high side, but it runs fine through 50 feet of coax. This is the one I used; https://www.amazon.com/gp/product/B005AME7Y8
    You need to make sure that your power injector can pass through a 1.5gHz signal, that is the down converted signal from the LNB.

    From the LNB power supply, you then have your RTL-SDR. Anything that will work at 1.5gigs should be fine for a test, but you really need something that is stable and sensitive. If you find something that works, stick with it.
    This is the one I am using; https://www.amazon.com/gp/product/B0129EBDS2
    Again, I have nothing to compare it with. (I just wonder if this is not the source of the drift I am fighting with).

    I chose to use SDR#, its free, simple to install and basic enough to do the job. Sure, you can get fancy and run some other software, but its mostly a headless setup, so simple is better.

    Once you have the signal, you need to decode it. I only know of one application that can do it, Jaero. Jonti’s work is amazing, be sure and give him a few bucks if you go this way.
    What you do with the information I will leave it to you. There seems to be two main paths, Plane Plotter or VRS (Virtual Radar Server). I went with the second option since that’s what I already run (I also run PP, but not to the same extent as VRS).

    Ok, so that’s the easy part, now getting it to all play nice together and get planes on a map……

    We bought the dish new off eBay. it arrived, free shipping, in two weeks from Canada.
    Took me about 2 hours to put it together, seems pretty straight forward. If I had to do it again, I would get at least 6 foot and something that mounts on a pole, not a base.

    The LNB was brand new from Amazon. Long story short, it was faulty. I spent a week working with it for hours and saw nothing but static.
    One evening I just gave up and voided the warranty and opened it up. Sure enough, it had a dry joint and was open circuit on the input. A quick touch with a hot soldering iron and put it back together (interesting note aside, the heat sink is there for looks only, it has zero contact with any parts – made me smile a little).

    After spending a week looking at nothing but noise, once I powered it back up I was met with wall to wall signals, it was very exciting and a big ups that I was not losing my mind.

    SDR#. Install it and run it.

    Now the really hard part. What frequency should you tune for? In the end, I could not really find a solid answer since it depends on the down converted frequency of the LNB and the specific satellite you are tuned to. I am looking at Inmarsat 4-F3.

    There are a few lists floating around, but they did not agree and in the end it was a single screen shot on Jonti’s website that got me close.
    it helps to look and see what sort of waterfall pattern the adsb messages makes as well. I mostly went by visual on the waterfall more so than the frequency.
    I wish I had something more solid to give you than ‘look for this pattern’, but that’s really what it came down to. I just could not find anyone that had documented the frequencies for the different sats with the LNB I was using.
    Here are some examples from my setup.

    This next one is a bit more zoomed in on the frequency scale and shows you both the frequency I was tuned to and what the waterfall looks like.

    Now for the next hard part. Aiming the dish.
    A few things to try.
    You can get a compass and inclination meter and point it using those. Not a bad way to do it, and I got in the ball park with this method, but it was not really accurate enough. BTW, the metal in the base will throw things off, so use a plank of wood to extend the dish and put the compass at the end of the wood to get more accurate.
    You can also use one of the satellite aligning apps on your phone. I also did this and found it really good.
    Here is a screen shot looking next to the satellite. (I found the arc of geostationary satellites really fascinating).

    The third way takes a little more gear, but is rather interesting (thanks again go to Jonti for his description of this method), disconnect the LNB and put a modified GPS patch antenna at the center of the feed horn and tune your SDR to the L-Band signals coming from the sat. Now you can pretty easily move your dish around for peak signal from the sat.
    Here is some of the gear I used to test this.
    GPS patch antenna, LNA and bias T injector.

    Here it is on the feed-horn.

    I also did this to see what it was like and it works pretty well.
    So in the end, I used all three options to get the dish pointing in the right rough direction.

    By now, you should have a pretty solid waterfall of signals, find the short staccato signals and start to tweak things for maximum signal.
    One important thing to note, Jonti mentions that I would need the bit of dielectric stuffed in the feed-horn to turn from direct (horz or vert) polarization to circular. He is right. Listen to him. The key is to get it inserted the correct way, there are two ways to put it in, they are 90 deg to each other (up and down or left right if you have the ‘heat sink’ uppermost).
    Make sure you test both ways. One way will make the signal weaker, the other way will make the signal stronger. No dielectric will be somewhere in the middle. You clearly want the strongest of the options.

    Hone in on a likely looking signal and fire up Jaero and see what gets decoded.
    As far as setting it up for the basics, you need to select 10500 bps burst and I found the best decoding to happen when the locking is set to 1800 or 900 hz and AFC is on. (Note, this may or may not make much of a difference. But please experiment with it. I am finding some differences but need more time with it testing).
    Set SDR# to 10500 bandwidth (or wider, but not narrower) and USB.
    You should start to see ACARS data. If in the SU’s tab you see a LOT of ‘Bad R/T Packet’ messages, you are close, but don’t have things setup quite right. Go back over my notes and take a look at my settings and yours.

    IMPORTANT NOTE. In this screen shot I have ‘Locking’ set wrong. It should be 1800 or even 900.

    Once you are getting good clean ACARS data you should straight away notice that you are getting a lot of reports with Lat/Long in them.
    We can push these messages to another bit of software and get the final goal of all this, planes on a map.

    If you are using Plane Plotter, Google will guide you. I cant help.
    If you are using VRS, here is how you set things up…..

    Jaero is a little ‘odd’ in that you set the Basestation address to be You can change the port number, but you MUST leave the IP address to be all zeros.
    This is the odd bit and cost me a ton of time, but in the end, Jonti himself set me straight in a very kind email.

    (Note. In this screen shot I have the ACARS option ticked and its going to the same PC as VRS on a different port number. You wont need to do this for just ADSB.
    I am also interested in looking at the ACARS data in Node-RED. Read about it on my aircraft page.)

    In your VRS then, you need to put the IP address of the PC running Jaero (assuming its on a different PC, if its the same, then its just and the port number) and the port number you picked.
    Of course the type has to be Basestation. Tick the box, ‘Is Sat-com’ to give yourself the longer time out.

    Ok, Phew. By now you can take a breath and check out some amazing data flowing in. You should, within just a few minutes (yes, it really does happen that fast) see planes from all over the world (just about). The foot print of the satellite is amazing.

    Want to double the amount of data/planes you are getting?
    Notice that there is another ADSB signal next to the one you are on….. If you tune over it you will see much the same ACARS/ADSB data but from different aircraft.
    Install the VFO plugin for SDR# and also install VAC (Virtual Audio Cable).
    Now you can set 1 cable for the main frequency and 1 for the VFO.
    Now copy paste a second instance of Jaero on the desktop, right click and set its properties to be -s line2 and now you can start another instance of it and have double the messages.

    Here is the key, you cant run them both on the same port number. The second instance still must be but the port number MUST be different for each instance.
    So set up a second receiver in VRS and make sure you are getting another set of data / aircraft.
    Then set up a merged feed with the two feeds into one to see the total of the two frequencies.

    1. The output of the LNB drifts. I don’t know if its due to temperature, PLL instability or Doppler from the sat moving or drift in the RTLSDR. At the moment I have to tweak the VFO in SDR# a few times a day. This will not do. I need to solve this asap.
    2. The satellite drifts in a slow figure 8 pattern. The dish needs re pointing a few times over 24 hours. At the moment, it looks like just in elevation. I have a linear actuator on order and will see about automating it as a matter of some urgency.

    Hope that helps. I have written what I found scatted all over the place, a lot of what was not written anywhere and the rest is what I wish was written down somewhere.

  • Satellite Dish

    After much back and forth between Freddy and myself, we settled on a dish.
    I needed a 6 foot, she said 4 foot, so we bought a 5 foot, that way neither of us got what we wanted.

    Unfortunately, the guys website with the most information is currently down, so I cant link you to it… But the short of it is aircraft tracking.
    There is a geostationary satellite that re-transmits aircraft positions for aircraft over the oceans. The sat I am going to tune into is over Hawaii and so will get aircraft over the Pacific. It should pick up data from planes that are entering my current system so is perfect.

    We will be moving from the middle of the lawn where I put it together into the garden where it should hopefully be less obvious over the weekend.
    Once there we will need to align it and then tune into the data stream.
    All of which sounds a lot easier than I expect it to be.
    The data comes in bursts, so its going to be hard to find and tune into.
    More details to come…. But enough to say, I have been looking forward to this project for about 3 years.

  • Inmarsat ACARS

    Sorry guys, did not realize that I had not blogged about my Inmarsat fun and games…..

    There are a few different ways that aircraft communicate back and forth with the airline.
    This blog is about satellite.
    There is a geostationary (not moving, very handy, no tracking needed) satellite named Inmarsat (sorry, forget the exact number, there are a few of them) that carries, among other things, aircraft data.
    To pick it up you need a small dish, an antenna, SDR (software defined radio) and a computer to run some software.

    First things first. As it happens, I knew this day was coming so have been collecting satellite dishes behind the shed for a while, turns out I kinda lot track and have about 5 of them back there…. hey, its good to have options.

    Next, you need an antenna or feed horn. So I did what all good hackers do and wound one around a toilet roll.

    Next up, attache it to the dish and see if you can get some signal.
    And we did, but the mounting was a bit unsustainable and looking out the window was also not the best, but here is how it looked for the test.

    Next thing to try was jamming it in attic.
    Let me tell you about the nice words that were expressed in getting the dish through the manhole and aligned to look at the satellite.

    There is alfoil over the roof and it really killed the signal…..
    Freddy came up with the idea of putting a pole on the side fence and hiding it behind some bushes out there, so thats what did.

    Finally we had a good strong signal and a nice solid mount.
    The eagle eye among us might notice that the feed horn is not the toilet roll. And your right.
    I modified a GPS antenna and its much better as its smaller, flat and has better gain.
    So with a 30 foot long USB lead, we now have a signal in the garage where we can use the software JAERO to decode the signal and stream it to my main dashboard.

    You can see it here; http://thebaldgeek.net:2880/ui/#!/4

    Long term my plan is to get another GPS antenna and have a second decoder running to double my data rate.

    So yeah, that’s how I pick up aircraft text messages from space.
    Cool beans.

  • Noisy computers?

    We have been interested in building a one stop shop website for all things aircraft tracking and decoding for some time.
    To this end we have put up a satellite dish to get Inmarsat messages, 136mHz antennas for ACARS and VDL data and for HF we have been running an Alinco receiver.

    Everything has been working great, but I have always struggled with a really high HF noise (static) floor. It massively impacts my ability to pickup and thus decode the weak signals coming from the aircraft all around the world (the radio at this frequency – 6mHz – can hear aircraft from pretty much around the globe). I have been tinkering with the antenna and noise suppressors and all sorts of things, but it has always not been great.

    The last straw was when this guy commented about my HF reception;
    (At the very bottom of that thread/comment.)
    1% of the traffic. Ouch.
    But he was right, I had a feeling I was not doing great. Getting around 70 messages a day from aircraft.
    I honestly suspect any one or all of the 90 or so computer devices that are running 24×7 at the house.

    Anyway, buddies to the rescue.
    I have been chatting with two guys from Phoenix a fair bit and one of them is big into both aircraft and HF and he also noticed that he was getting more traffic than I was, but he lacked the computer skills and gear to decode them.
    So yeah, we made a deal. If he picked up the signals, I would decode them.
    Thus he has dedicated one of his radios to aircraft and I wrote some code to transfer the raw data from his place to mine where I do further decoding and display it on my website.

    BOOM! I cant believe it but we went from 70 a day to 3000+ a day.
    We are now almost drowning in lovely lovely aircraft data from around the world.
    Both he and I are thrilled.

    You can see the data here; http://thebaldgeek.net:2880/ui/#!/5
    Its been running great for the week or so and neither of us see why that won’t be the case for a good while longer.