This should be the main link instead of the hackaday article. Fascinating stuff.

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".

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.

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.

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.

>> 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.

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.

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.

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.

A lot cheaper to have a drone loitering at 50,000 feet.

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.

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.

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.

>> 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.

> 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.

[0] https://youtu.be/m-YSPHib-kg?t=89

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?