Return to Video

Hillbilly Tracking of Low Earth Orbit

  • 0:00 - 0:09
    silent 30C3 preroll titles
  • 0:09 - 0:12
    applause
  • 0:12 - 0:15
    Travis Goodspeed: First I need
    to apologize for typesetting this
  • 0:15 - 0:20
    in OpenOffice. I know that the
    text looks like a ransom note.
  • 0:20 - 0:25
    But that’s what happens
    when you don’t use LaTex.
  • 0:25 - 0:28
    I’d also like to give a shoutout to
    Collin Mulliner if he is here,
  • 0:28 - 0:30
    and our Dinosaur rock band.
  • 0:30 - 0:33
    laughs, applause
  • 0:33 - 0:37
    We’re a Christian rock band, we’re
    called ‘Jesus lives in the ISS’ and
  • 0:37 - 0:46
    we know that he is always watching us,
    but we think that it’s easier for him
  • 0:46 - 0:50
    to hear our prayers when
    he’s, you know, in an orbit
  • 0:50 - 0:56
    that passes over us. So we need to use
    orbital tracking to know when to pray!
  • 0:56 - 0:58
    laughter
  • 0:58 - 1:01
    As I’m sure you can guess I’m not
    recognized as a legal minority religion
  • 1:01 - 1:06
    in Germany. I’d also like to thank skytee
  • 1:06 - 1:11
    and Fabienne Serrière and Adam Laurie
  • 1:11 - 1:17
    and Jim Geovedi for some
    prior satellite tracking work,
  • 1:17 - 1:20
    and the Scooby Crew at Dartmouth
    College for all sorts of fun
  • 1:20 - 1:25
    whenever I bounce out there.
    This is the mission patch
  • 1:25 - 1:28
    of the Southern Appalachian
    Space Agency (SASA).
  • 1:28 - 1:34
    applause and cheers
  • 1:34 - 1:37
    This was drawn by Scott Beibin and there
    are a few pieces of my people’s native
  • 1:37 - 1:43
    culture that I need to point out here. On
    the right the little Dinosaur type thing
  • 1:43 - 1:48
    with his finger going out, you might
    call him E.T. but we call these things
  • 1:48 - 1:52
    ‘buggers’. They are like this tall, and
    they are green and that’s why the man
  • 1:52 - 1:56
    on the left has a shotgun.
    laughter
  • 1:56 - 2:01
    Because he doesn’t want to be abducted.
    You got a satellite dish in the middle
  • 2:01 - 2:04
    and it’s sitting on sinter blocks because
    that’s also a piece of my people’s
  • 2:04 - 2:10
    native culture. There’s a moonshine
    still in the background.
  • 2:10 - 2:15
    That’s kind of like Vodka but you
    make it at home and from corn.
  • 2:15 - 2:20
    And then there’s the mountain… a piece…
    it looks like there are snow peaks
  • 2:20 - 2:25
    on those mountain tops. But our mountains
    aren’t tall enough to have snow.
  • 2:25 - 2:29
    These are actually that we’ve blown off
    the lids of the mountains for coal mining.
  • 2:29 - 2:32
    Which is another piece of
    my people’s native culture.
  • 2:32 - 2:37
    And at the top, in space you can see
    the ISS, and you can see a banana,
  • 2:37 - 2:42
    and you can see what I think is a bulb.
    This is to signify space trash.
  • 2:42 - 2:46
    I mean there’s a lot of stuff up there.
    And, you know it’s symbolism that matters
  • 2:46 - 2:51
    in these things, you know?
  • 2:51 - 2:55
    At BerlinSides, in May of 2012
  • 2:55 - 3:01
    I did a lecture on reverse-
    engineering the SPOT Connect.
  • 3:01 - 3:05
    The SPOT Connect is a little
    hockey puck type thing
  • 3:05 - 3:09
    – this is what it looks like.
    And these things are great.
  • 3:09 - 3:14
    It weighs a bit more than your cell phone
    but it runs off of a couple of batteries,
  • 3:14 - 3:18
    it connects to your phone by Bluetooth.
  • 3:18 - 3:22
    Originally these were emergency locator
    beacons. So if you’re going hiking…
  • 3:22 - 3:25
    have any of you seen the movie where
    the guy has to cut off his arm
  • 3:25 - 3:31
    with a dull knife? If you’re hiking and
    you don’t want that same experience
  • 3:31 - 3:34
    you buy one of these things. And
    then there’s an emergency button
  • 3:34 - 3:39
    you can push that transmits your
    GPS coordinates by satellite
  • 3:39 - 3:44
    to rescue workers. But that was boring,
    so they had to add social media.
  • 3:44 - 3:47
    laughs, laughter
  • 3:47 - 3:50
    So in addition to keeping you
    from chewing off your own arm
  • 3:50 - 3:55
    this device will also allow you to
    tweet and make Facebook posts.
  • 3:55 - 4:00
    laughs, laughter
  • 4:00 - 4:05
    The idea is that as you’re running…
    here I’m crossing the Schuylkill River
  • 4:05 - 4:10
    in Philadelphia and the Android
    phone on the left is making a post.
  • 4:10 - 4:16
    And I did an article on reverse-
    engineering the Bluetooth side
  • 4:16 - 4:22
    of these things. Because… I use a weird
    brand of phone that Microsoft killed off,
  • 4:22 - 4:28
    and I’m terribly bitter about it. But
    I also figured out the physical layer.
  • 4:28 - 4:35
    And that’s what this diagram shows.
    This transmits at 1.6125 GHz.
  • 4:35 - 4:41
    And it sends a pseudo-random stream, so
    each one of these zeros is a long chunk
  • 4:41 - 4:44
    where it’s bouncing back and forth
    between two different frequencies.
  • 4:44 - 4:49
    And the same for the ones.
    But the way that the pattern works
  • 4:49 - 4:55
    is that it switches the signal whenever
    it is going from the 0 signal
  • 4:55 - 4:59
    to the 1 signal. And internally, there are
    these little pops that you can actually
  • 4:59 - 5:04
    identify on a software defined radio
    recording. And this is how you can
  • 5:04 - 5:08
    reverse-engineer the signal that
    the SPOT Connect is sending up
  • 5:08 - 5:15
    to its satellite network.
  • 5:15 - 5:18
    Everything is clear text on this.
    And it’s completely unencrypted.
  • 5:18 - 5:25
    It just has your serial number, your GPS
    coordinates, and a bit of ASCII text.
  • 5:25 - 5:30
    So if you listen on this frequency and
    you have the correct recording software
  • 5:30 - 5:34
    you can actually watch all of the SPOT
    Connect messages that are transmitting
  • 5:34 - 5:40
    up from your location. And this would be
    great except that this is designed for
  • 5:40 - 5:44
    hiking in areas where there’s no cell
    phone service. So having an antenna
  • 5:44 - 5:48
    on the uplink frequency is kind of
    useless. You know you would actually
  • 5:48 - 5:52
    have to go out to a national park, find
    some guy who is about to chew his arm off,
  • 5:52 - 5:56
    and then you could listen to his uplink
    where he is like tweeting: “Hey, I’m gonna
  • 5:56 - 6:01
    chew my arm off”, you know?
    laughter
  • 6:01 - 6:10
    So that’s great as a proof of concept
    but it’s not really anything practical.
  • 6:10 - 6:13
    The current state of that was that I knew
    the protocol and I could sniff the uplinks.
  • 6:13 - 6:17
    But I wanted to sniff the downlinks. So
    it’s easy for me to get the thing that
  • 6:17 - 6:22
    goes up to the satellite. But what I wanted
    was what comes down from the satellite.
  • 6:22 - 6:27
    And that requires a satellite dish. But
    a geo-stationary dish isn’t good enough
  • 6:27 - 6:32
    because the satellites that run this
    network – there are a lot of them,
  • 6:32 - 6:38
    it’s called the Globalstar network,
    they fly really low across the earth,
  • 6:38 - 6:43
    and they fly across the earth in very
    tight, very fast orbits. So they’ll move
  • 6:43 - 6:49
    from horizon to horizon in 15 to 20
    minutes. Which means that you either need
  • 6:49 - 6:54
    like a sweat shop army of kids
    trying to aim the satellite dish
  • 6:54 - 7:01
    as it’s going across or you need
    to make it computer-controlled.
  • 7:01 - 7:04
    Stepping back from the SPOT
    Connect for a little bit, and
  • 7:04 - 7:08
    discussing some prior research.
    Adam Laurie did some work
  • 7:08 - 7:12
    with geostationary satellites.
    These are the satellites that stay
  • 7:12 - 7:16
    in one position in the sky.
    He gave two sets of talks
  • 7:16 - 7:24
    – one in 2008 and the second in
    2010. And he used a DVB-S card
  • 7:24 - 7:28
    connected to a satellite dish with
    a DiSEqC motor, so that it could move
  • 7:28 - 7:34
    the satellite dish left and right in order
    to scan a region of the horizon.
  • 7:34 - 7:37
    His tool is publicly available,
    it’s called satmap.
  • 7:37 - 7:41
    You can grab it at this URL.
  • 7:41 - 7:46
    And then after he finds a signal he has
    a feed scanner. Normally when you use
  • 7:46 - 7:51
    Satellite TV your provider gives you
    a listing of the frequencies, and
  • 7:51 - 7:58
    your provider gives you an exact orbital
    position to aim your satellite dish at.
  • 7:58 - 8:02
    But Adam’s tool allows you to scan to
    see which frequencies are in use and
  • 8:02 - 8:07
    which protocols are in use, once
    you’ve correctly aimed your dish.
  • 8:07 - 8:10
    And he also describes a technique
    for moving your dish left and right
  • 8:10 - 8:16
    while doing this in order to
    identify where the satellites are.
  • 8:16 - 8:20
    This recording here is from
    a re-implementation that I made
  • 8:20 - 8:24
    of Adam’s work, in order to
    catch up with it. In this diagram
  • 8:24 - 8:30
    the x-axis – because you move left
    and right – that shows the azimuth,
  • 8:30 - 8:35
    that shows how far left or right my
    satellite dish has moved. And then
  • 8:35 - 8:41
    the y-axis shows the frequency. And
    all of these dots are strong signals.
  • 8:41 - 8:48
    So every vertical bar in which you see
    chunks of frequencies, that’s a satellite.
  • 8:48 - 8:52
    But these stay in the same position. So
    it’s easy for me to repeat this experiment.
  • 8:52 - 8:57
    It’s easy for me to re-run it, and to find
    the same satellites in the same position.
  • 8:57 - 9:05
    It’s easy to debug this.
    But it can’t move in elevation.
  • 9:05 - 9:08
    This diagram is actually
    a very small slice of the sky.
  • 9:08 - 9:14
    We’re looking at a single line,
    maybe 10 degrees across.
  • 9:14 - 9:18
    Maybe only 5 degrees across.
  • 9:18 - 9:23
    So hacking Ku-band – the television
    satellites – has the advantage
  • 9:23 - 9:27
    that you can use cheap standardized
    hardware. I bought one of these DVB-S cards
  • 9:27 - 9:34
    in Mauerpark, in Berlin for 3 Euro. You
    can use standardized DiSEqC motors,
  • 9:34 - 9:37
    you can buy them at a satellite TV shop.
  • 9:37 - 9:42
    TV signals come with video feeds
    so you can actually see pictures.
  • 9:42 - 9:46
    There was a scandal about 4..5 years
    ago where they were finding
  • 9:46 - 9:50
    drone [control] feeds that were being
    bounced across these satellites.
  • 9:50 - 9:57
    In the nineties it was very popular to
    listen to the sort of unedited sections
  • 9:57 - 10:00
    of interviews, when people would
    be interviewed over a satellite,
  • 10:00 - 10:05
    before Skype and such
    things became options. And
  • 10:05 - 10:09
    there are also networking signals here
    using TCP/IP packets. So you can actually
  • 10:09 - 10:14
    turn your DVB-S card into
    a promiscuous ethernet adapter,
  • 10:14 - 10:18
    and start sniffing all of the traffic that
    comes across. This is also a great way
  • 10:18 - 10:24
    to get free downlink bandwidth. Because
    you can just flood packets at an address
  • 10:24 - 10:28
    that, you know, will be routed to
    you, or several addresses, and
  • 10:28 - 10:33
    then you sniff it out as the
    legitimate receiver ignores them.
  • 10:33 - 10:37
    But it also has some disadvantages. It
    only works for geostationary satellites.
  • 10:37 - 10:41
    If the satellite is not staying in the
    same position relative to the ground
  • 10:41 - 10:47
    then you can’t track it. Your
    dish also moves very slowly.
  • 10:47 - 10:50
    And it only moves left and right.
    It won’t move up and down.
  • 10:50 - 10:53
    And you’re limited to standardized
    signals. So while it’s great that you get
  • 10:53 - 10:59
    video and TCP/IP you’re never
    going to get anything weird.
  • 10:59 - 11:05
    You’re not gonna get any mobile
    data, you’re not going to get any
  • 11:05 - 11:11
    Brazilian truck-drivers – we’ll
    get to those in a bit. laughs
  • 11:11 - 11:16
    I misspoke, you actually will get
    Brazilian truck-drivers in this.
  • 11:16 - 11:19
    So I bought a satellite dish. One of the
    best things about living in America is
  • 11:19 - 11:26
    that you can buy industrial
    hardware cheap as dirt on ebay.
  • 11:26 - 11:29
    I know things aren’t likely used to being
    a cat bite to (?)(?) human children anymore.
  • 11:29 - 11:33
    But this satellite dish here on
    the left – the one in the radome –
  • 11:33 - 11:41
    that’s my dish. And to the right,
    that’s the boat that it came from.
  • 11:41 - 11:50
    applause
    laughs
  • 11:50 - 11:54
    This came from a military ship.
    But the dish itself is also available
  • 11:54 - 11:58
    for civilian use on very large yachts.
  • 11:58 - 12:02
    The dish itself is a Felcom 81 and it
    was intended for use with a network
  • 12:02 - 12:08
    called Inmarsat. Inmarsat allows
    for telephone connections,
  • 12:08 - 12:13
    and also data connections when you’re on
    a boat. So if the crew wants to call home
  • 12:13 - 12:18
    or wants to go to AOL Keywords
  • 12:18 - 12:24
    or whatever was popular back when
    this was common they could do that.
  • 12:24 - 12:28
    And the dish was designed to sit
    at the very top of a ship’s mast.
  • 12:28 - 12:32
    The reason why is that at the top of
    the mast there aren’t any obstructions
  • 12:32 - 12:35
    – it has a clear view of the sky in all
    directions. But there’s a complication
  • 12:35 - 12:39
    with being on the top of the mast. Which
    is that the ship is rocking beneath you
  • 12:39 - 12:44
    and you’re moving more
    than the rest of the ship.
  • 12:44 - 12:48
    So they have stepper motors
    for azimuth, elevation and tilt.
  • 12:48 - 12:53
    And then they have spinning gyroscopes.
    Back before the iPhone there was
  • 12:53 - 12:58
    this dark, dark time when
    gyroscopes actually spun.
  • 12:58 - 13:02
    And this is the sort of gyroscope that
    it has. It actually has 4 of them so
  • 13:02 - 13:06
    that it can measure its movement.
  • 13:06 - 13:11
    And then it has a control computer. So the
    idea is that the dish itself can be moved
  • 13:11 - 13:16
    while remaining absolutely stable
    with regard to the gyroscopes.
  • 13:16 - 13:20
    So it compensates for the rocking of
    the ship beneath it as it’s targeting
  • 13:20 - 13:28
    a stationary satellite.
    In America this costs 250 dollars
  • 13:28 - 13:32
    but it’s electronics equipment, so while
    you think that would only be a 180 Euro
  • 13:32 - 13:40
    it’s more like 2500. And that’s before
    import duties and it being impounded.
  • 13:40 - 13:45
    We also have this lovely culture in which
    people love excuses to use their trucks.
  • 13:45 - 13:51
    So the guy that I bought this from offered
    to deliver it to my home for only $200.
  • 13:51 - 13:57
    It was an 11-hour drive.
  • 13:57 - 14:00
    But if you wanted this you’d have to
    bring it back in your carry-on luggage
  • 14:00 - 14:06
    and that could be awkward.
  • 14:06 - 14:09
    I got this dish and I decided I had
    to do something with it. So I created
  • 14:09 - 14:15
    the Southern Appalachian Space Agency.
    I’m from the state of Tennessee,
  • 14:15 - 14:20
    formerly known as the State of Franklin
    until North Carolina invaded us.
  • 14:20 - 14:22
    It’s ok, I know Europeans suck at history.
  • 14:22 - 14:30
    laughs
    laughter and applause
  • 14:30 - 14:33
    Now I’m trying to think of how to show
    you on a map where Tennessee is
  • 14:33 - 14:37
    without having a map. But, you know,
    it’s okay, I know you suck at geography
  • 14:37 - 14:40
    and will forget it soon. (?)
  • 14:40 - 14:42
    From audience: It’s very
    near Texas, to the north.
  • 14:42 - 14:48
    Travis: Texas is our first colony. But
    it’s actually a decent drive to the east.
  • 14:48 - 14:53
    Due east (?). You don’t
    actually have to go it anyways.
  • 14:53 - 14:58
    So what I did was I took these motors
    which were designed to be able to move
  • 14:58 - 15:03
    the satellite dish to compensate
    for the rocking the ship and
  • 15:03 - 15:10
    I re-purposed them to track through
    the sky while the ground is stable.
  • 15:10 - 15:13
    We don’t have very many earthquakes in
    Tennessee. The last one that we had
  • 15:13 - 15:18
    made rivers run the wrong direction.
    But it’s okay – it’s a geography thing.
  • 15:18 - 15:22
    laughs
    So this allows me to track things
  • 15:22 - 15:26
    that are moving through the sky.
    But it doesn’t actually matter
  • 15:26 - 15:30
    where they’re moving in the sky because
    that’s just a software problem.
  • 15:30 - 15:36
    So in addition to tracking objects that
    are in low-earth orbit by a software patch
  • 15:36 - 15:42
    I can also track things that are in deep
    space. It’s not much harder to track
  • 15:42 - 15:48
    deep space probes or stars than it
    is to track items in low-earth orbit.
  • 15:48 - 15:53
    And then I added a software defined radio
    which allows me to record a signal now
  • 15:53 - 15:58
    and then demodulate it later.
    Which is necessary if you intend
  • 15:58 - 16:03
    to reverse-engineer a signal. Because
    a lot of the downlinks from these satellites
  • 16:03 - 16:08
    are completely non… completely
    undocumented. And being able
  • 16:08 - 16:11
    to tune in to the right frequency is only
    half of it. You also need a recording
  • 16:11 - 16:16
    of sufficient quality that you can
    reverse-engineer it after the fact.
  • 16:16 - 16:20
    We’re sort of spoiled by software
    defined radios in that when doing
  • 16:20 - 16:27
    software defined radio work we usually
    have a very good signal to work from.
  • 16:27 - 16:34
    So having high quality signals for later
    reverse-engineering is necessary.
  • 16:34 - 16:39
    I really wanted to be able to identify
    undocumented downlinks for low-earth orbit
  • 16:39 - 16:44
    in the same way that we already
    do this for geo-stationary orbit
  • 16:44 - 16:50
    using tools like the ones that Adam
    Laurie and Jim Geovedi made.
  • 16:50 - 16:54
    So I built a software framework as
    a collection of Python daemons.
  • 16:54 - 16:59
    And these run across a home
    area network in my house.
  • 16:59 - 17:04
    There’s a Beaglebone inside of the Radome.
  • 17:04 - 17:10
    And an x86 server in the house. Or AMD64,
    whatever the kids call it these days.
  • 17:10 - 17:13
    And then I used Postgres for coordination.
    So that all of these daemons can talk
  • 17:13 - 17:19
    to each other without… without me really
    caring which machine they’re on.
  • 17:19 - 17:26
    So for maintenance I can have my
    laptop pretending to be the dish,
  • 17:26 - 17:31
    and I can have stepper motors on my desk,
    and I can watch them spin, and I can even
  • 17:31 - 17:35
    make a model of the dish and swap these
    components in and out without the rest of
  • 17:35 - 17:43
    the network being confused. This also
    allows for SQL injection attacks to
  • 17:43 - 17:48
    physically move my dish. Which is why the
    sensor network is not on one of those
  • 17:48 - 17:53
    fancy WEB 2.0 things. Because of you could
    inject, say, “UPDATE target SET name=
  • 17:53 - 17:56
    ‘VOYAGER 1’”. Then my dish would physically
    move and start tracking Voyager 1
  • 17:56 - 18:01
    through the sky. Voyager 2
  • 18:01 - 18:07
    doesn’t actually come into the sky because
    of my position in the Northern hemisphere.
  • 18:07 - 18:11
    So, it’s okay, I know you suck at
    geography. But Voyager 1 is going up,
  • 18:11 - 18:15
    and Voyager 2 is going down.
  • 18:15 - 18:19
    There’s a Realtek software defined radio
    for the radio reception. Although
  • 18:19 - 18:24
    these things are garbage. So I’m in the
    process of replacing this for the HackRF.
  • 18:24 - 18:30
    There’s also an EiBot board for motor
    control. We’ll get back to that in a minute.
  • 18:30 - 18:35
    And there’s an Inertial Measurement Unit
    from VectorNav which actually measures
  • 18:35 - 18:40
    using the fancy MEMS gyroscopes and
    a MEMS compass how I’m moving.
  • 18:40 - 18:45
    This isn’t accurate enough to target
    the dish, so I’m still counting steps
  • 18:45 - 18:50
    to move the dish. But it is accurate
    enough to tell me when my belts
  • 18:50 - 18:57
    have broken. Or when I’m up
    against a physical obstruction.
  • 18:57 - 19:02
    This is skytee helping
    me out with the dish.
  • 19:02 - 19:05
    He’s zip-tying it. Because, you know
    we know everything about duct tape
  • 19:05 - 19:07
    where I come from, but we don’t know
    anything about zip-ties. So I had
  • 19:07 - 19:11
    to bring in a German engineer.
    laughter
  • 19:11 - 19:14
    We call him a gerry wigger(?)
    but, you know…
  • 19:14 - 19:20
    This is the satellite dish itself. And you
    can sort of see in this photograph
  • 19:20 - 19:25
    where we’ve strapped on the equipment.
    There’s like an umbilical cord.
  • 19:25 - 19:30
    Or more like a spinal column that actually
    runs up the back of the dish. So we just
  • 19:30 - 19:37
    added new cables onto that line.
    And then zip-tied them in place.
  • 19:37 - 19:42
    And skytee came up with all these
    crazy ideas like that we should use
  • 19:42 - 19:47
    chains and zip-ties to make sure that the
    cables don’t tear themselves out. And
  • 19:47 - 19:52
    that worked tremendously well in practice.
    So, as this thing spins around,
  • 19:52 - 19:58
    by the original design there’s a ring
    connector that all of the signals
  • 19:58 - 20:01
    go through. That all of the networking
    goes through. That all of the rest
  • 20:01 - 20:06
    goes through. And that worked in the
    nineties because it had no reason
  • 20:06 - 20:11
    to send anything faster than 9600 baud.
  • 20:11 - 20:18
    But with the modern signals going across
    it I need 100 MBit/s or even GB ethernet,
  • 20:18 - 20:22
    that’s not enough, I need more than
    two wires. So there’s a cable that comes
  • 20:22 - 20:25
    across it, and then I rely on the
    software to keep it from wrapping
  • 20:25 - 20:31
    that cable around itself. So it can only
    move, say, 400 degrees around.
  • 20:31 - 20:35
    But that’s still more than a full circle.
    So by stopping halfway and moving back
  • 20:35 - 20:40
    I can prevent it from getting snagged.
  • 20:40 - 20:43
    We’ve got the Beaglebone on the left,
    in the middle there’s a USB hub
  • 20:43 - 20:48
    and on the right is the motor controller.
  • 20:48 - 20:53
    The Beaglebone runs Debian Linux and
    takes care of sending the software defined
  • 20:53 - 21:00
    radio recordings over the network. It also
    takes care of updating the motor positions
  • 21:00 - 21:06
    to be the ones that the database
    declares should be current.
  • 21:06 - 21:13
    The stepper motors themselves are the
    originals that the dish was designed with.
  • 21:13 - 21:18
    And they’re running to an EiBot Board.
    The EiBot board was intended
  • 21:18 - 21:25
    for plotting on Easter eggs
    laughs, laughter
  • 21:25 - 21:28
    I feel, you know… is that neat?
  • 21:28 - 21:33
    laughs
    applause
  • 21:33 - 21:38
    So you can actually aim a satellite dish
    that’s as tall as you are, with of these
  • 21:38 - 21:42
    fancy motors using less sophisticated
    equipment than what’s used
  • 21:42 - 21:47
    in a 3D printer. Don’t panic, though.
  • 21:47 - 21:51
    It’s a hell of a lot more
    reliable than a 3D printer.
  • 21:51 - 21:55
    But we needed some sort of backup in
    addition to the inertial measurement unit
  • 21:55 - 21:59
    telling us when the device
    had snagged itself.
  • 21:59 - 22:05
    It would also help to have
    a visual queue. Because
  • 22:05 - 22:10
    the satellite dish sits in Tennessee, and
    while I love my home town, and, you know
  • 22:10 - 22:15
    I’m very proud of being Tennessean, it’s
    also a long way to travel when you need
  • 22:15 - 22:21
    to re-orient the dish. Using an
    accelerometer it’s easy enough
  • 22:21 - 22:26
    to correct the elevation. Because you can
    use the accelerometer as a level, and
  • 22:26 - 22:31
    you can use that to tell how high up the
    dish is pointing, at an absolute scale.
  • 22:31 - 22:38
    But the compass isn’t very accurate. So
    instead, as a backup we have a webcam
  • 22:38 - 22:44
    that’s taped to the top. Taping
    is my people’s native culture.
  • 22:44 - 22:48
    We have it taped to the top, and then
    it’s pointing backwards. So this gives us
  • 22:48 - 22:52
    like a rear view camera,
    from the dish’s position.
  • 22:52 - 22:57
    So as the dish sits
    inside of its radome…
  • 22:57 - 23:01
    – junk cars in the yard are also
    my people’s native tradition!
  • 23:01 - 23:04
    laughs, laughter
  • 23:04 - 23:10
    So the dish sits there next to
    my brother’s Toyota Supra.
  • 23:10 - 23:14
    And that thing, you know,
    that thing flies as soon as it gets
  • 23:14 - 23:18
    an engine put back in it.
    laughter
  • 23:18 - 23:22
    So it sits there and it’s moving but
    externally you can’t see where it is.
  • 23:22 - 23:26
    Which means that I can’t call my family
    in Tennessee and blackmail them into
  • 23:26 - 23:30
    – yet again – looking at my dish to tell
    where it’s pointed. There are bolts
  • 23:30 - 23:33
    that hold this down, it takes half an hour
    to remove the lid, another half an hour
  • 23:33 - 23:37
    to put it back on.
  • 23:37 - 23:43
    So instead we took the radome…
    that’s Frank, he’s my cat.
  • 23:43 - 23:46
    Give a “Cheers!” for Frank!
  • 23:46 - 23:52
    applause and cheers
  • 23:52 - 23:56
    Yeah, we had such a great time with Frank.
    And we never knew that she was pregnant.
  • 23:56 - 24:03
    If you happen to need kittens and wanna
    pay the customs fees I’ll hook you up!
  • 24:03 - 24:11
    So then we took tape and ran tape
    down the edges of the radome,
  • 24:11 - 24:15
    and then marked it. So from the markings
    you can tell which clock position
  • 24:15 - 24:20
    the back of the satellite dish is pointing
    at. So if you point the dish towards 12:00
  • 24:20 - 24:26
    you know that you’re roughly at 6:00,
    so you know that it’s pointing South.
  • 24:26 - 24:29
    And then you can sort of scan the sky
    for a stationary target, and navigate
  • 24:29 - 24:33
    off of that, to recover your position.
  • 24:33 - 24:40
    Software-wise… remember, the
    whole thing runs through Postgres,
  • 24:40 - 24:46
    so I just tunnel the Postgres over SSH,
    and then I wrote a Python client
  • 24:46 - 24:52
    that displays the satellite positions
    and the satellite state in PyGame.
  • 24:52 - 24:55
    This is intended for making those games
    where you see the rabbit and the rabbit
  • 24:55 - 25:01
    jumps on the other rabbit. But it… works!
    And it works perfectly well enough
  • 25:01 - 25:05
    to target the dish. Because all that this
    software has to do is plot the positions
  • 25:05 - 25:11
    of the satellites, and give orders back to
    the database when I click on a satellite
  • 25:11 - 25:15
    or click on a position.
    It can also display stars.
  • 25:15 - 25:21
    So the red items are satellites which are
    not selected. The green item is GOES-3
  • 25:21 - 25:25
    which is the satellite that I’m targeting.
    And then the white items are
  • 25:25 - 25:32
    stars in the sky. Now this is
    a plot in which the azimuth
  • 25:32 - 25:37
    is on the X axis, and the elevation is on
    the Y axis. But I can also arrange it
  • 25:37 - 25:42
    into a polar plot. Which sort of gives me
    an upside-down view of the satellite dish
  • 25:42 - 25:48
    looking at the sky.
    I doubt you can read it but
  • 25:48 - 25:55
    just above the green circle in the center,
    that’s Polaris which is the North star.
  • 25:55 - 25:59
    It’s also weird because, you know,
    working on this, you know, I thought
  • 25:59 - 26:02
    that I got really good at astronomy
    until I realized that I only knew
  • 26:02 - 26:08
    what the stars looked like during the day.
    laughter, laughs
  • 26:08 - 26:12
    And it being PyGame you can
    actually run it on a mobile device.
  • 26:12 - 26:18
    So the same client that runs on my
    laptop can also run on my Nokia N900.
  • 26:18 - 26:26
    laughs
    applause
  • 26:26 - 26:33
    A significant portion of the GUI client for
    this was written while stuck on the U-Bahn,
  • 26:33 - 26:38
    connected over 3G, SSH through
    and just using emacs on the phone.
  • 26:38 - 26:45
    laughter, laughs
    applause
  • 26:45 - 26:49
    If you’re one of those people who needs to
    complain about the N900 being too old,
  • 26:49 - 26:54
    it also runs on the N9.
  • 26:54 - 26:59
    And then you can take the data out of this
    and run it through scientific software.
  • 26:59 - 27:03
    In addition of the software defined radio
    recordings themselves being dumped out
  • 27:03 - 27:10
    to a text file or a binary file on disk
    you can also dump out things like
  • 27:10 - 27:15
    the received signal strength indicators
    (RSSI). So this is a screenshot in which
  • 27:15 - 27:18
    I’m identifying different satellites that
    I’ve seen in the sky based upon
  • 27:18 - 27:23
    their downlink signal peaks. You can see
    the noise floor there, at the bottom,
  • 27:23 - 27:28
    and then there’s a rather strong signal on
    the left. And a weaker, narrower signal
  • 27:28 - 27:35
    on the right. Now, the
    daemons that build this up…
  • 27:35 - 27:38
    you need an orbit prediction daemon.
    Because you need to know
  • 27:38 - 27:41
    where the satellites are and where
    they’re going, and where they will be
  • 27:41 - 27:46
    by the time you get to them.
  • 27:46 - 27:51
    You need to update the orbits themselves.
  • 27:51 - 27:55
    LEO satellites are described in TLE files,
  • 27:55 - 27:58
    these are called ‘Two Line Entry’ and
    they’re called ‘Two Line Entry’ because
  • 27:58 - 28:02
    they’re three lines long.
    laughter
  • 28:02 - 28:08
    These were originally used by NORAD for
    inter-continental ballistic missile tracking.
  • 28:08 - 28:11
    And because a ballistic missile
    is basically in orbit, it’s just that
  • 28:11 - 28:15
    that orbit happens
    to collide with the earth.
  • 28:15 - 28:20
    But this format isn’t terribly accurate
    for satellites that adjust their own orbit.
  • 28:20 - 28:27
    So anything that has fuel, or has engines,
    or changes mass will vary its position.
  • 28:27 - 28:34
    And this also doesn’t account for drag.
    Because, you know, the missile itself,
  • 28:34 - 28:38
    you know it goes up it goes down, it’s
    not orbiting enough for the light drag
  • 28:38 - 28:43
    in the upper atmosphere to matter. But for
    a satellite it does. So these Two Line Entries
  • 28:43 - 28:48
    will work for a matter of days or maybe
    a couple of weeks. But they don’t last
  • 28:48 - 28:55
    longer than that. So you need a daemon
    that grabs the new files from Space Track.
  • 28:55 - 28:58
    And this is just a matter of like
    a recursive WGET, and then
  • 28:58 - 29:03
    parsing the files. And that still needs
    to be done. You also need motor control,
  • 29:03 - 29:07
    because you need to move the dish
    physically to track your target.
  • 29:07 - 29:11
    You need input for the Inertial
    Measurement Unit. This comes over
  • 29:11 - 29:15
    a low voltage serial port. And then
    you need radio daemons to handle
  • 29:15 - 29:21
    spectrum analysis or downlink recording.
    And these you’ll have several of them,
  • 29:21 - 29:29
    you have to swap them out. So you’ll begin
    by using the spectrum analyzer to identify
  • 29:29 - 29:34
    that your aim is accurate, that you’re
    accurately tracking the targets
  • 29:34 - 29:38
    well enough to get a recording from
    them. And then after that you begin
  • 29:38 - 29:42
    to take software defined recordings off
    them. And, eventually, you might have
  • 29:42 - 29:48
    a standalone application that parses
    what you’re receiving. Such as
  • 29:48 - 29:56
    the Osmocom guys did with OpenGMR.
  • 29:56 - 30:00
    So for orbit prediction I began
    with a DOS program that had been
  • 30:00 - 30:05
    ported to Unix, called PREDICT.
  • 30:05 - 30:10
    And this worked, but it’s garbage.
  • 30:10 - 30:16
    It only supports 20 satellites plus the
    sun, the moon, Venus and Mars.
  • 30:16 - 30:24
    But no other planets because it’s
    designed for astronomy photographers
  • 30:24 - 30:29
    who want to get a picture of something
    as it comes over the horizon. You know,
  • 30:29 - 30:34
    I need to track hundreds of targets and
    then write a script to opportunistically
  • 30:34 - 30:38
    pick the ones that I want to record.
    Because otherwise you have to like
  • 30:38 - 30:45
    set an alarm clock for the half-hour pass
    in which you can play with something.
  • 30:45 - 30:49
    That software does allow you to query the
    results by UDP, though. So you can just
  • 30:49 - 30:55
    send it a flood of request packets,
    then it will flood back with the data
  • 30:55 - 31:01
    you’re looking for. So I switched to
    a library called PyEphem which allows you
  • 31:01 - 31:06
    to track hundreds of birds. It has no
    UDP nonsense. It will also calculate
  • 31:06 - 31:13
    satellites, planets and stars.
    And the really nifty thing about this
  • 31:13 - 31:18
    is that you tell it… you know, it being
    a library you tell it when to update
  • 31:18 - 31:23
    the individual object that you’re
    interested in. So you can update
  • 31:23 - 31:27
    objects that are out of view or
    uninteresting more slowly
  • 31:27 - 31:33
    than the ones that you care about.
    So I managed to track every single item
  • 31:33 - 31:39
    in geo-stationary orbit. This thick
    ring here is the Clarke Belt
  • 31:39 - 31:47
    of all satellites in geo-stationary orbit,
    as viewed from my Southern horizon.
  • 31:47 - 31:54
    applause
  • 31:54 - 31:58
    The Two Line Entry files you can get
    freely from CELESTRAK.COM.
  • 31:58 - 32:02
    So this is just a simple script that
    grabs them and then inserts them.
  • 32:02 - 32:07
    And the prediction daemon will actually
    select them as it is loading up.
  • 32:07 - 32:14
    Because all inter process communication is
    running through this Postgres database.
  • 32:14 - 32:17
    And this daemon can be moved to
    a different machine if I needed
  • 32:17 - 32:22
    more computing power, or anything
    like that. The motor control demon…
  • 32:22 - 32:27
    well, the EiBot board is designed to take
    stepper motor commands. It shows up
  • 32:27 - 32:33
    as USB Serial device on Linux. So as
    I plug it in to the Beaglebone it appears
  • 32:33 - 32:42
    as /dev/ttyACM0. And the baud rate doesn’t
    matter. Because this is a USB device.
  • 32:42 - 32:49
    You could then send it simple commands.
    Like ‘SM,3000,500,-400’ means that I wanna
  • 32:49 - 32:56
    move a stepper motor for 3000 ms. I want
    the first motor to move 500 forwards,
  • 32:56 - 33:03
    that’s UP, and the second one to move
    400 LEFT which is backwards 400 steps.
  • 33:03 - 33:08
    And then it will count that out, and
    then it sends me back an OK.
  • 33:08 - 33:12
    If I want to disable the motors, I send
    ‘EM,0,0’. This allows the motors to be
  • 33:12 - 33:16
    freely spun. Because normally a stepper
    motor will physically hold its position,
  • 33:16 - 33:22
    you need to turn them off in
    order to slide the dish around.
  • 33:22 - 33:28
    ‘EM,1,1’ will enable both motors
    in 1/16-of-a-step mode.
  • 33:28 - 33:31
    Stepper motors can do fractional
    steps because they’re
  • 33:31 - 33:38
    holding themselves in position.
  • 33:38 - 33:41
    You can see the motors themselves
    with the belts and the gear train.
  • 33:41 - 33:47
    This thing on the right would probably
    be illegal for me to turn on.
  • 33:47 - 33:53
    The thing on the right is a 250 W
    amplifier. laughter
  • 33:53 - 33:59
    The stepper motors themselves just have
    six wires. In a lot of 3D printer type stuff
  • 33:59 - 34:03
    they ignore the middle two. So you just
    drop off the middle two wires, you run
  • 34:03 - 34:07
    the other four to your stepper
    controller, and you’re good to go.
  • 34:07 - 34:10
    The belts and stuff need to be measured
    in order to figure out exactly
  • 34:10 - 34:17
    what the gear reduction is. Because you
    need to know how many steps form a degree.
  • 34:17 - 34:23
    The IMU unit, this Vectornav VN100,
    it’s a MEMS gyroscope and accelerometer
  • 34:23 - 34:28
    and a compass in a single box.
    It costs $500 which was
  • 34:28 - 34:34
    more than all of the other
    equipment put together.
  • 34:34 - 34:37
    The compass is confused by the stepper
    motors because the compass is measuring
  • 34:37 - 34:40
    magnetic fields. So you need to
    mount this physically as far away
  • 34:40 - 34:46
    from the stepper motors as possible. And
    the gyroscope is confused by motor jerk
  • 34:46 - 34:50
    which is a shame because stepper motors
    work as a series of jerks rather than
  • 34:50 - 34:57
    as a single consistent motion. And the
    accelerometer is confused by gimbal lock,
  • 34:57 - 35:01
    so you have to switch it to
    a quaternion mode in order to get
  • 35:01 - 35:06
    consistent values out of it. And if I had
    to do this over again I’d really try
  • 35:06 - 35:11
    to drop this piece of garbage. But it’s
    a lovely technology when it works.
  • 35:11 - 35:12
    some laughter
  • 35:12 - 35:19
    Now for position calculations: the
    elevation itself comes from the IMU,
  • 35:19 - 35:24
    the azimuth comes from the motor daemon.
    This is because the accelerometer
  • 35:24 - 35:30
    can very accurately tell which way
    the earth’s gravity is pulling it
  • 35:30 - 35:34
    whereas the accelerometer has to integrate
    jerks over time in order to figure out
  • 35:34 - 35:39
    its position. So the
    accelerometer will drift
  • 35:39 - 35:46
    and the compass will be confused by the
    magnetic fields while the elevation is
  • 35:46 - 35:53
    just a single accelerometer
    that doesn’t drift.
  • 35:53 - 36:00
    And the IMU will become
    a backup for these things
  • 36:00 - 36:03
    in order to figure out how to make
    it reliable. But at the moment
  • 36:03 - 36:09
    the position measurement is infinitely
    more reliable. The tilt motor
  • 36:09 - 36:14
    I’m not using at present because on
    a ship that’s rocking it’s necessary
  • 36:14 - 36:20
    to tilt the dish. On a satellite dish
    that’s staying still the only useful
  • 36:20 - 36:26
    tilting the dish is so that you can follow
    the arc of a satellite through the sky
  • 36:26 - 36:30
    by only moving a single motor.
    Photopgraphers do this when they’re
  • 36:30 - 36:35
    trying to get long exposures of moving
    satellites. At the moment my software
  • 36:35 - 36:39
    doesn’t support this feature. But
    if it turns out to be necessary
  • 36:39 - 36:44
    to get higher quality
    recordings I might add it.
  • 36:44 - 36:47
    There are radio daemons. The
    first is a spectrum analyzer.
  • 36:47 - 36:51
    This just measures the signal strength
    on each frequency. And it does it by the
  • 36:51 - 36:58
    power spectral density function.
  • 36:58 - 37:03
    And the strength itself will
    vary with the position error.
  • 37:03 - 37:07
    So this allows you to figure out how
    far off you are by sort of testing,
  • 37:07 - 37:10
    by overshooting just a little bit,
    or undershooting just a little bit
  • 37:10 - 37:15
    to center on your target. The downlink
    recorder dumps the IQ values
  • 37:15 - 37:20
    in the software defined radio
    directly to an NFS share,
  • 37:20 - 37:25
    which can later be decoded and
    read and reverse-engineered.
  • 37:25 - 37:30
    We’ve got a whole table of spectrum
    data. And then I plot that in a tool
  • 37:30 - 37:37
    called Viewpoints which NASA releases
    for dealing with giant scatter plots
  • 37:37 - 37:44
    in multiple dimensions. Each view takes
    two dimensions, and it’s tons of fun.
  • 37:44 - 37:48
    The client GUI is this PyGame. I have
    Postgres for communications, and
  • 37:48 - 37:52
    the server does all the heavy lifting,
    so the Beaglebone itself never has
  • 37:52 - 37:58
    to do anything complicated with
    regards to software defined radio.
  • 37:58 - 38:04
    This is also about these faint blue lines
    are positions at which I’ve seen
  • 38:04 - 38:10
    particularly strong signals in order to
    identify which satellites are active
  • 38:10 - 38:14
    and which ones are inactive.
    Because satellites die over time.
  • 38:14 - 38:18
    And particularly useful targets we’re
    reverse-engineering are satellites that are
  • 38:18 - 38:23
    out-of-commission or outdated.
    I’m running out of time by these markers.
  • 38:23 - 38:25
    Does that mean that we’re skipping
    questions, or does that mean that
  • 38:25 - 38:29
    I need to be off the stage?
    mumbling to stage
  • 38:29 - 38:36
    Not having Q&A, okay. So today I get
    accurate tracking of satellites.
  • 38:36 - 38:41
    And this thing can run unattended 24h
    a day for months without maintenance.
  • 38:41 - 38:46
    Like I said: it’s nothing like a 3D printer.
    laughter
  • 38:46 - 38:50
    It takes software defined radio
    recordings, it can provide maps
  • 38:50 - 38:55
    of views of different
    satellites in the sky.
  • 38:55 - 39:00
    The next step is I want to publish
    a ‘port scan’ of the entire sky.
  • 39:00 - 39:04
    So which frequencies are in use on which
    birds, for every bird that ever comes
  • 39:04 - 39:08
    above Tennessee, on every
    downlink that fits my antenna
  • 39:08 - 39:12
    as well as a database of software
    defined radio recordings. If anyone
  • 39:12 - 39:19
    would care to donate a truckload
    of disks – that might be handy.
  • 39:19 - 39:23
    I’d also like to make other ground
    stations. The software that I’ve written
  • 39:23 - 39:26
    ought to be portable to new hardware.
    So there’s nothing that should keep you
  • 39:26 - 39:31
    from being able to port this to run on
    your own dish. And I have a large yard,
  • 39:31 - 39:37
    so I could conceivably have
    a dozen of these things.
  • 39:37 - 39:39
    Another way that you can do it, and
    the way that it’s traditionally done
  • 39:39 - 39:45
    for, say, cube satellites is having
    Yagis or other loosely directional antennas
  • 39:45 - 39:49
    in order to receive the signals.
    I went with a dish because I wanted
  • 39:49 - 39:55
    more selectivity. I wanted to be able to
    get reverse-engineerable recordings
  • 39:55 - 40:03
    rather than intentional ones for which
    I already knew the downlink protocol.
  • 40:03 - 40:08
    So this is my van, my van is amazing.
  • 40:08 - 40:16
    applause
  • 40:16 - 40:19
    Thanks to Nick Farr. I had a bit too
    much to drink in Montreal and
  • 40:19 - 40:24
    I called Nick Farr and I said: “Nick,
    I want a DUKW”, like these amphibious
  • 40:24 - 40:28
    troop transport vehicles. And Nick
    said: “Sorry, I can’t get you one but
  • 40:28 - 40:32
    you want a news van!” And I said:
    “Hell yeah, I want a news van!”
  • 40:32 - 40:35
    So – this pole in the background, that’s
    not a lighting pole. That’s actually
  • 40:35 - 40:43
    part of the van.
    laughter
  • 40:43 - 40:50
    This is the antenna retracted. This mast
    goes up 20 m by pneumatic power.
  • 40:50 - 40:55
    There’s an air compressor in the back.
    Here is the control panel,
  • 40:55 - 40:58
    there’s an air-conditioned
    office in the middle.
  • 40:58 - 41:02
    laughter, laughs
  • 41:02 - 41:09
    This has four 19" server racks as well
    as some A/V equipment that was left over.
  • 41:09 - 41:14
    I was particularly excited about the
    video monitor which supports PAL
  • 41:14 - 41:18
    which you folks are familiar with,
    NTSC or “Never The Same Color”
  • 41:18 - 41:22
    which is my people’s native culture…
    laughter
  • 41:22 - 41:26
    But most importantly, it does SECAM,
    the system essentially contrary
  • 41:26 - 41:30
    to the American method.
    laughs
  • 41:30 - 41:34
    laughter and applause
  • 41:34 - 41:41
    So in addition to my radio equipment
    I’m adding my Soviet PDP-11 which was…
  • 41:41 - 41:45
    laughs
    …and that’s not a joke. I have a Soviet
  • 41:45 - 41:52
    PDP-11 thanks to the kind folks at the
    Positive Hacking Days conference.
  • 41:52 - 41:58
    This is the control panel,
    and that’s my talk!
  • 41:58 - 42:13
    applause
  • 42:13 - 42:18
    Herald: Thank you so much.
    There actually is time for Q&A now.
  • 42:18 - 42:21
    Travis: Well, first I’d like to introduce
    you to my cat. If we could go back
  • 42:21 - 42:26
    to the prior image. This is Frank!
    We didn’t know it at that time, but
  • 42:26 - 42:32
    Frank was not dad (?) when this picture was
    taken. If you’d like kittens get in touch!
  • 42:32 - 42:35
    Okay. Are there any questions?
  • 42:35 - 42:39
    Question: Great talk. What’s the most
    interesting signal you decoded so far?
  • 42:39 - 42:45
    Travis: At the moment I’m sort of stuck
    at the L band range. Because of filters
  • 42:45 - 42:48
    that I have yet to remove. So everything
    gets attenuated, and becomes annoyingly
  • 42:48 - 42:55
    quiet outside of the 1.5 ..1.6 -ish range.
  • 42:55 - 43:00
    The Globalstar network is what I’m
    most interested in targeting next.
  • 43:00 - 43:03
    I can’t wait to see what
    people are tweeting
  • 43:03 - 43:07
    while they should be enjoying nature.
  • 43:07 - 43:09
    Herald: Is there a question
    from the internet?
  • 43:09 - 43:13
    Signal Angel: Yeah, the internet has
    many questions. So first one was:
  • 43:13 - 43:18
    Is there really no authentication or
    encryption on the Q band IP services?
  • 43:18 - 43:25
    So you can just spoof at will? And…
  • 43:25 - 43:29
    can the birds see the physical
    location of the source
  • 43:29 - 43:35
    accurately enough to
    find who is spoofing?
  • 43:35 - 43:41
    Travis: I’m not an expert in Ku band. The…
    for the downlink the bird has no clue
  • 43:41 - 43:46
    as to the location of the dish. Because
    you’re only listening. They can roughly
  • 43:46 - 43:50
    figure out your geographic area because…
    they need to figure out where
  • 43:50 - 43:54
    the spot beam is going. So they might know
    whether you’re in, say, Germany or
  • 43:54 - 44:02
    in France. But they won’t know whether
    you’re in Heidelberg or Mannheim.
  • 44:02 - 44:07
    They do have forms of authentication for
    many satellite networks. Satellite TV
  • 44:07 - 44:12
    is one of the best-protected network
    services because of the satellite wars
  • 44:12 - 44:17
    in the nineties in which TV pirates would
    fight back and forth with smart card
  • 44:17 - 44:23
    designers. But there are also many
    unencrypted links. And there are…
  • 44:23 - 44:31
    because of standard protocols those
    are particularly easy to find in Ku band.
  • 44:31 - 44:37
    Question: You’ve been talking about
    using RTLSDR from osmocom.
  • 44:37 - 44:42
    And you were talking about your spectrum
    analysis program. Is this one working
  • 44:42 - 44:46
    with RTLSDR?
  • 44:46 - 44:54
    Travis: So… RTLSDR… so I’m using
    the RTLSDR, not the OsmoSDR.
  • 44:54 - 44:59
    Which are separate. The spectrum
    analyzer is working with the RTLSDR.
  • 44:59 - 45:03
    My complaint about the RTLSDR is that
    when you have a strong signal next to
  • 45:03 - 45:08
    a weak signal the weak signal is
    utterly useless for interpretation.
  • 45:08 - 45:13
    Question: Okay. Thank you.
  • 45:13 - 45:15
    Herald: Another question
    from the internet?
  • 45:15 - 45:19
    Signal Angel: Okay, next question from
    the internet is: How do you record
  • 45:19 - 45:24
    the radio signal from the dish,
    at what sampling rate?
  • 45:24 - 45:30
    Travis: The RTLSDR samples at 2 million
    samples per second. As soon as I switch it
  • 45:30 - 45:37
    over to the HackRF I’ll be having
    20 million samples per second.
  • 45:37 - 45:42
    The sampling rate can be reduced once
    the bandwidth of the signal is known.
  • 45:42 - 45:46
    For reduced storage. And the
    recordings can also be compressed.
  • 45:46 - 45:53
    But it’s still a hell of a lot of storage.
  • 45:53 - 45:55
    Herald: Any other questions?
  • 45:55 - 45:58
    Signal Angel: The internet
    has more questions…
  • 45:58 - 46:00
    Herald: Okay…
  • 46:00 - 46:04
    Signal Angel: Did you look into obtaining
    a capacitive high-bandwidth coupler as used
  • 46:04 - 46:10
    for the rotary gantries in CT scanners?
    Those can apparently transmit contactless
  • 46:10 - 46:13
    several GBytes per
    second, bi-directionally.
  • 46:13 - 46:16
    Travis: I’ve not looked into those.
    It seemed better to have an umbilical
  • 46:16 - 46:22
    cable and to be careful not to snap it.
  • 46:22 - 46:26
    The whole thing was done for a budget
    of less than 2000 Dollars, and can be
  • 46:26 - 46:32
    recreated for less than a budget of 1000
    [Dollars]. And they… so we tried to avoid
  • 46:32 - 46:36
    fancy parts. The local radio shack loved
    us because we’d swing in and buy all sorts
  • 46:36 - 46:40
    of crazy stuff. As soon as we told them
    that we wanted the satellite dish to
  • 46:40 - 46:41
    dance Gangnam style…
    laughs
  • 46:41 - 46:49
    laughter
  • 46:49 - 46:51
    in German, strong accent:
    Danke, gerne!
  • 46:51 - 46:54
    applause
  • 46:54 - 46:57
    silent postroll titles
  • 46:57 - 47:03
    subtitles created by c3subtitles.de
    in the year 2017. Join, and help us!
Title:
Hillbilly Tracking of Low Earth Orbit
Video Language:
English
Duration:
47:03
  • I will stop now. Please continue my work, thanks!

  • I will stop now. Please continue my work, thanks!

English subtitles

Revisions Compare revisions