GPS antenna mods make Starlink terminal immune to jammers
hackaday.comThis should be the main link instead of the hackaday article. Fascinating stuff.
So "immune to jammers" seems to be hyperbole; perhaps "more resistant to jammers" wuld be a more accurate phrasing.
It's really a question of distance, which is not mentioned in the article. Russian style is to park jammer vehicles pretty much evenly spread out on a line behind their defensive boundary.
I'll easily believe "immune to Russian GPS jammers as typically deployed when used X kilometers behind active battles".
Does Starlink have a mode where you can manually tell it its lat/long? For a semi-stationary receiver, surely that would be a better way to bootstrap a connection.
I would assume that Starlink needs the GPS signal more for timing than for position though it certainly does need to know its position as well. Some of it is probably also driven by regulatory and UX requirements -- from a consumer standpoint there is a benefit of using GPS reception as a checkpoint before the process proceeds. Under normal operation if the terminal can't receive GPS then it is likely also unable to communicate with Starlink satellites.
One could use a GNSS emulator and this modification to test how the system performs under various GPS fault conditions to quantify it. My hunch is that it's more of a regulatory check than an operational requirement. I suspect the signals from the Starlink satellites themselves are sufficient for the terminal to derive timing and position without having to rely on GPS at all.
I'm currently messing around with a u-blox timing chip, the LEA-6T. It (and many other slightly-above-consumer grade u-blox chip) has a "survey-in" mode, where you tell it "yes, you are stationary" and it essentially averages into a fixed location. This was a $30 chip from China and it gets to 4cm accuracy in 10 min with a $10 antenna. Do that once and you have a location. If the chip reboots, you can either survey-in again, or just tell it where it is.
Highly likely the GPS module inside the Starlink device has this ability. Whether or not that functionality is exposed is up to the Starlink engineers I suppose.
Survey-in won’t help if your system is being jammed.
Question: How come aircraft can so easily get jammed then? They use GPS for precise positioning in flight, so I'm guessing they have the very best antennas...
GPS jamming defense in the US is mostly provided by the FCC bringing the hammer of God down on people who run GPS jammers. The penalties for interfering with navigation signals are severe.
HAMMER OF GOD[1][2][3][4][5]
[1] https://www.fcc.gov/general/jammer-enforcement
[2] https://www.fcc.gov/document/fcc-fines-florida-driver-48k-ja...
[3] https://www.cnet.com/culture/truck-driver-has-gps-jammer-acc...
[4] https://www.fcc.gov/document/fcc-upholds-fine-jammer-used-bl...
[5] https://docs.fcc.gov/public/attachments/DOC-339560A1.pdf
GPS signal is comparatively weak. The satellites are far away, and terrestrial signal sources can be much stronger.
> They use GPS for precise positioning in flight
Large airliners, for the most part, don't. They use inertial navigation. GPS is a source of calibration for their inertial navigation system. There are some (non-precision) approaches that use GPS.
Question: Would using GPS antenna that only points at the sky (vs more omni-directional ones that mobile devices must have to work in any position) would "fix" the jamming problem ?
>> GPS antenna that only points at the sky
On paper. In reality, most every antenna has "side lobes" through which jamming signals can spoil the actual signal. In some cases the more directional an antenna becomes, the more significant are the side lobes.
That's essentially what he's doing. The patch antenna he's using have a null at the horizon, where ground-based jammers would be.
OK, thanks. That info wasn't in TFA, nor in the article it linked to.
It is in the linked-to article, including discussion about lobes, polarization, more directional replacement antennas, and comparative measurements while being jammed.
https://olegkutkov.me/2023/11/07/connecting-external-gps-ant...
I can't find it in a quick Google, but I read an article a while back talking about them putting the receivers in foxholes; can see the sky just fine, but any ground-based jammers nearby have to push through the dirt.
Remember that GPS satellites may be near the horizon relative to you. That said there are enough of them in orbit that you can usually get away with only using the ones that are more overhead.
Why does Starlink need to use GPS if it can use its own satellite constellation to make time of flight measurements?
The linked-to original article says GPS works better and faster.
> Calculating position based on Starlink constellation requires more resources, and it’s not so fast. Plus, It can’t be used correctly in motion. Accumulated errors may be so significant that Starlink will not be able to work.
Do StarLink satellites have the same level of clock stability and precision that GPS satellites do? IDK but I really doubt it.
Surely, a satellite in orbit could easily jam Starlink boxes on the ground.
Maybe, but unless your goal was to deny service to a small, fast-moving window of the earth's surface you would need quite a lot of these.
If I was a nation state adversary, I’d put pretty high on my TODO list getting a handful of jamming satellites with a decent power supply at geostationary locations above all my adversaries.
Since a single geostationary satellite has line of sight covering about 1/3 of the planets surface, I bet if they had a decent sized reactor onboard and a well thought out transmitter/antenna array, the ROI would look pretty good.
And I’m just some random punter.
That is not feasible at a cost any current nation state could afford. Due to the inverse square law, the power output requirements to achieve any noticeable jamming from geostationary orbit would be enormous. There have been limited tests of fission reactors in space but they are too complex to operate reliably unattended for long. So, satellites are going to limited to solar or RTG power.
Only if using old school ‘blanket the area’ monopole antennas or if the goal was to cover the entire potential area all at once -but that seems unlikely to be desirable most of the time.
Phased arrays and beam steering would allow them to pick and choose the area at will with high resolution - or even specific targets like several hundred airliners at once.
Notably, the same things that starlink needs for being able to properly track base stations and communicate at the timescale/numbers it needs, and the tech is widely used in everything from cell phone towers to military.
Starlink has it a lot easier due to LEO, but they’re also a private company with a much harder problem and on a shoestring budget compared to a nation state.
TDP would be a lot lower if they could get it focused well enough. And it wouldn’t need to be operating all the time - a ‘war’ mode vs sleep mode seems like it would work too.
When not jamming, it could be a passive signals intelligence platform.
Or build a couple dozen and put in a lower orbit. Not like it would make a dent in China or Russias military budget, or require any tech newer than 20 years old for them.
> Or build a couple dozen and put in a lower orbit. Not like it would make a dent in China or Russias military budget, or require any tech newer than 20 years old for them.
Look at this animation[1] for a moment (click the >> or >>> button to speed up) and think about what it would actually take to get "in front" of enough satellites to block out a given geographic region; even just a single city. There are hundreds of satellites in each orbital plane, rapidly cycling through and taking each others' place.
You obviously cannot have counter-satellites in a geosynchronous "position", and you also can't have satellites simply move between greatly different orbits (or phases of existing orbits) willy nilly; The delta-V requirements are just too great. This just isn't a feasible strategy.
Given the wavelengths and distances involved there are severe physics limits to how much beams can be steered and focused. These aren't lasers. What you are proposing isn't practical at a cost any nation state can currently afford.
You seem really invested in ‘no one could afford it’, even at lower orbits.
Which seems pretty hilarious considering how much is getting spent on all this tech, and how much of an arms race it clearly is.
Especially considering how TS programs in general are usually a decade or two ahead tech wise anyway.
[https://www.defenseone.com/threats/2022/04/dia-warns-chinas-...]
If you think there aren’t surprises hiding in the Chinese or Russian’s pockets on this front, you’re far more optimistic than I.
Maybe they’ll just shoot down all the GPS satellites though.
> there are severe physics limits to how much beams can be steered and focused.
Are you skimming over this part? Of course enemy nation states have invested in jamming capability... just not on this front
And are you skimming over the part where I said lower orbit would still be cheap?
While not responding to my other comments?
A lot cheaper to have a drone loitering at 50,000 feet.
>> IMMUNE TO JAMMERS
No. That is not a thing. At most, one can make equipment less susceptible to jamming. Jamming is not like hacking, it isn't a matter of whether an attack works or does not. It cannot be fixed via a patch. Pump out enough energy close enough to the target and even a hyper-directional antenna can be jammed.
Have a look at military GPS jammers. They aren't the little dongles that you can buy online and run off USB battery packs.
Right, look at the US' current jammer suite, the AN/ALQ-99, while it has issues it's unbelievably powerful. One of the downsides is that it jams the AESA radars of friendlies in the area, including the plane using the jammer itself.
The next gen replacement sounds like an absolute monster too, but without some of the donwsides like the need for a ram air turbine to power it.
Fun fact: Airborne Jammers like these might be one of the last places of state of the art technology where the good old vacuum tube is still better than semiconductors.
For large power amplifiers, especially with power and power-density considerations, nothing beats a travelling wave tube.
And on the ground with "unlimited" power and cooling? Well, there's always the Klystron...
> One of the downsides is that it jams the AESA radars of friendlies in the area, including the plane using the jammer itself.
So you just lob in a heat seeker at the middle of the noise, and hope.
Then again, if you have an airborne source of jamming, you know you have bigger problems following. How much effort do you spend trying to knock out the jamming vs preparing for what is inevitably following? Flying in jammers from the opposite direction of an attack to draw in fighters to the wrong area is as elementary as attack options go.
> So you just lob in a heat seeker at the middle of the noise, and hope.
There's already another category of missile for that:
and Iraq I, Iraq II, and UKR-RUS have shown that they freakin work
It's even easier than that. You use a missile (or bomb) programmed to lock onto the source of the jamming.
Except the jammer oversaturates your receiver or even burns it out. Or causes it to see ghost targets.
The heat seeker would have problems unless you launched from behind it, which would be problematic if you're launching from the ground, depending on the jamming plane. A steathly plane with the heat sources minimized might not be detected by a heat seeker if launched towards an oncoming source
heat seekers havent been rear aspect only in decades, all aspect IR missiles are the norm now. the main issue is that most NATO IR missiles are very short range. much easier to instead program your radar guided missile to lock the big glowy thing and explode in its face
And that is an airborne radar, which is limited to the power generated by its little fan. A dedicated ground-based jammer might be plugged into a generator hauled on the back of a flatbed truck.
Atomic clock and hard coded GPS Location for the win?!
You joke, but have fun ensuring your clock is synced to everyone elses, even if it is incredibly accurate...
Good luck syncing a clock at a random location on the ground with one in orbit. In a warzone. Without a connection to the sat with which you are trying to sync.
What do you mean, with a directed signal? I guess it still is a problem of signal to noise ratio even then, if the jammer is powerful enough.
But how do these jammers work? They can't point at the sky to blind the satellite because there's no receiver; they broadcast from above ground, so in theory putting your receiver in a metal box with the top removed solves the problem?
>> putting your receiver in a metal box with the top removed solves the problem
No. Radio can turn around corners. It can also bounce off things. Radio is light, but at a much longer wavelength. It is less like blocking a laser and more akin to blocking out sound waves. Blocking line-of-sight to the transmitter would block the laser but would do little to block sound waves.
Yeah high frequency sound is a good analogy. Starlink is in the 11&40GHz region with wavelengths measured in cm which is about the equivalent to 20kHz.
The other really annoying thing about radio waves is that even relatively long wavelengths can leak through really narrow cracks (<1mm) if they are long enough (eg a wavelength) in the right polarization.
GPS is on 1575.42 and 1227.60 Mhz, though.
Isn't that above the critical frequency you'd get ionosphere reflection at? (Which makes sense, since the signals are coming from outside it at LEO)
> But how do these jammers work?
Pretend you're having a conversation. Now pretend you're having a conversation at a concert/club/any loud place. So like this[0]
> so in theory putting your receiver in a metal box with the top removed solves the problem?
You'd think so, but not actually. Think about it this way: you're trying to toss a ball into a cup (or box).
Is it easier or harder if that cup has a wide mouth or a narrow one? Make it V shaped for easier visualization and we'd be talking about the angle of that cone. Obviously the wider one right? The extreme other end of this is like a carnival ball tossing game where the cup is just as big (or they cheat and its smaller) than the ball you're trying to throw in. Now pretend you're trying to make that shot from a moving car. You come from far away and drive right past it and you get more points in this game the more shots you score.
That's analogous to what then satellite is doing. Remember it comes from over the horizon and then passes to the other horizon. You want to maximize your viewing angle because that gives the satellites more chances to make contact. This is more complicated because you need to kinda do this in parallel as you're handing off data collection to the next satellite coming through so the better viewing angle the more chances you have to smoothly negotiate that pass over.
Then there's the whole issue that we're talking about waves instead of particles but I'll let someone else handle that. You can actually find some cool visualizations on the internet about these. See knife edge diffraction.
In theory - but the satellites move, so your box needs to move, signals bounce (both off the ground and the air) and you can put the jammer in the air, too.
Also, the more directional you get, the more it may be possible to determine where you are.
Wait, starlink is one way? How does it know what to send?
This is about the GPS antenna on the starlink terminal. GPS is one-way. The terminal needs that GPS signal to predict where the starlink satellites are going to be at a given time.
The real "hack" answer is to bypass the GPS system and just feed the starlink terminal its true/known ground position/timing.
you use your 14.4 dial-up modem for sends. Oh, sorry, thinking about HughesNet.
GPS satellites don't "send" your coordinates to your receiver. Your receiver is just listening to the broadcast signal from several (usually 4+) satellites and based on the strength of that signal determining how far it is from each of those satellites. Which means the receiver is able to triangulate it's own position.
Strength of signal isn't used because strength is an unreliable measure of distance. The amount of atmosphere the signal passes through, reflection/refraction and all manner of weather effects will modify a signal's strength. So the sats transmit a pulse at a pre-agreed time and the receivers use the timing that they receive the signal as the measure of distance.
Pre-agreed time? Don't the satellites pulse a "The current time is x" signal?
With signals from 4 satellites one can triangulate oneself in 3D space, with 5 signals, in 4D! (3D + time). I once did the math and astounded myself that it worked.
If there is no agreed time then you don't know when the signals were sent and cannot make any sense out of the signal. They all have to send either in unison or according to a predetermined schedule. The synced clocks set that schedule.
The clocks are synced between satellites, but if your receiver is cold-booting in the middle of a forest, how does it know what time it is? It will receive a signal from 1 satellite that will say "I sent out this signal at time X", but you still don't know what time it is because you don't know how many nanoseconds it took for the signal to get to you, you can only be sure it's currently some time after X.
It will get another signal from another satellite, which could have the timestamp before X, because it left earlier and took longer to get to your receiver.
As I said, if you do the math, with 5 signals you can then determine your location in 3D space, and time!
> based on the strength of that signal
No, GPS positioning uses the precise time information encoded in the data from the satellites.
> Your receiver is just listening to the broadcast signal from several (usually 4+) satellites and based on the strength of that signal determining how far it is from each of those satellites.
GPS doesn't use the strength of the signal at all. Instead, each signal contains precise information about the current time at the highly-accurate atomic clocks onboard the corresponding satellite (plus some important metadata about each satellite, including things like their orbit parameters). If the receiver already knew the precise time, it could calculate the distance to each satellite from the difference between the true time and the received time (and the speed of the light), and 3 satellites would be enough to triangulate its position. Since the receiver usually doesn't know the precise time, it needs an extra satellite because there are now 4 unknowns (3 for its position plus 1 for the current time).
(Obviously, that's a very simplified explanation, there are plenty of other things which complicate the calculations.)
>and based on the strength of that signal
Wrong. Utterly wrong.
Would you explain why?
Here's a great explainer of GPS starting from really basic concepts.
By the time the signal reaches your GPS receiver, it is below the thermal noise floor of even amazing receivers. But each GPS satellite has a unique pseudo-random code (called a PRN) that is within the signal. Receivers that listen long enough can pick out the PRN and thus the GPS signal.
I'm no GPS expert, I've read some of the theory had enough of a working understanding to deal with tactical navigation systems, but that was in my past. I remember using El-Rabbany's "Introduction to GPS" text.
No. The Internet is at your fingertips.
an explanation not only helps the ignorant, it reinforces the idea within your own thoughts and perhaps seeds new ideas that are derivative; it even teaches the otherwise uncaring that may happen upon the comment.
what you did wasn't that -- but I would just like to point out that simple concise explanations helps the community as a whole; it's not just the ignorant that lose out.
Yes, I know it's likely not your job to educate, and maybe it's a bother that someone acts expert on something that they're clearly not -- but those that care to educate serve everyone in the context of an online forum, not just the naive or ignorant.
That's such a better response than LMGTFY