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GPS antenna mods make Starlink terminal immune to jammers

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Re: GPS antenna mods make Starlink terminal immune to jammers

#21

Post by fl7305 »

kbknapp wrote: post #18
dwighttk wrote: post #12

Earlier quoted context omitted.

Wait, starlink is one way? How does it know what to send?

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.

> based on the strength of that signal

No, GPS positioning uses the precise time information encoded in the data from the satellites.

Re: GPS antenna mods make Starlink terminal immune to jammers

#22

Post by nixgeek »

meindnoch wrote: post #20
kbknapp wrote: post #18

Earlier quoted context omitted.

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.

>and based on the strength of that signal Wrong. Utterly wrong.

Would you explain why?

Re: GPS antenna mods make Starlink terminal immune to jammers

#24

Post by kurthr »

sandworm101 wrote: post #14
baq wrote: post #9

Earlier quoted context omitted.

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.

Re: GPS antenna mods make Starlink terminal immune to jammers

#25

Post by sandworm101 »

kbknapp wrote: post #18
dwighttk wrote: post #12

Earlier quoted context omitted.

Wait, starlink is one way? How does it know what to send?

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.

Re: GPS antenna mods make Starlink terminal immune to jammers

#26

Post by jandrese »

mezeek wrote: post #11

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.

Re: GPS antenna mods make Starlink terminal immune to jammers

#27

Post by auspiv »

thrtythreeforty wrote: post #23

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'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.

Re: GPS antenna mods make Starlink terminal immune to jammers

#28

Post by jandrese »

adql wrote: post #2

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 ?

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.

Re: GPS antenna mods make Starlink terminal immune to jammers

#29

Post by looofooo0 »

sandworm101 wrote: post #5

>> 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…

Atomic clock and hard coded GPS Location for the win?!
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