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Comment by archerx | Hacker News Reader

If the GPS satellites are above the starlink ones how is Iran able to disrupt the GPS signals?

GPS signals are extremely weak, and they're necessarily received from omnidirectional antennas that can't provide much antenna gain. In some sense it's a miracle of signal processing that GPS can ever be received.

There have been developments in receiving antennas that are harder to jam.

Most jamming is horizontal and limited to a few bands. So by having a directional antenna and listening to all services for now it seems to work. But this is a cat and mouse game.

https://furuno.eu/gr-en/marine-solutions/gnss-positioning-ti...

By jamming the receivers on the ground

Ok that makes a lot of sense, thank you.

For legal reasons I base this off of nothing but just turn your jammer to the sky. Could get fancy and point out directly at the satellites since my understanding is it's pretty easy to know where they are.

Edit to add: I do not mean the GPS satellites or the starlink ground terminals. That was not the question so that is not my answer. I mean the starlink satellites

That doesn't work. GPS is broadcast, not bidirectional communication, so preventing the satellites from seeing the GPS receiver does nothing: they're not looking to begin with.

What are you talking about? The jammers are on the ground. Just like receivers on the ground can be jammed with bad RF nearby, so can receivers in space. You just point the bad RF towards the receiver

The GPS satellites aren't receiving anything. The GPS satellites transmit signals, and the starlink terminals (and other users of GPS) receive those signals.

Maybe he's implying they're literally cancelling out the waves like ANC headphones but with emf and a large geographic area.

Wellll you could technically jam their uplink channels, but doing so may get the US in your doorstep quite quickly

More to the point, to do that to this number of satellites on this big an area you'd need nuclear power plant levels of power, and it would only degrade GPS a bit (their clocks slowly desync when uplink is blocked)

My understanding was that each satellite broadcasts a coarse ephemeris for the whole network, and that that “almanac” isn’t accurate for very long (on the order of weeks). Without uploads to the satellites, those almanacs will go stale.

I don’t think the almanacs are necessary for the system to work, in theory. But I believe they’re commonly used by receivers to narrow down the range of possibilities when trying to find a PRN match for a signal they’re getting.

(I’ve dealt with GPS and similar navigation signals for work but am not an expert, this is just the impression I’ve gotten over a few years)

This is a great plot for a B movie or a trashy military action book. “The bad guys are jamming GPS uplink and we only have two weeks until the almanacs are out of date and the whole system breaks down. Millions of innocent Americans will drive into rivers by accident.”

Ok they said the GPS of the starlink satellites is being jammed, and the question was how. The comment I was replying to did not say the terminal, it said the satellite. Maybe that's the confusion

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