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Comment by toomuchtodo | Hacker News Reader

> A single observer can't really say for certain that jamming is happening; you need a distributed sample from multiple different sensors over a period of time to have reasonably high confidence.

Could you use RTLSDR triangulation to hone in on granular lat long of jamming sources?

https://www.rtl-sdr.com/detecting-gps-jammers-in-augmented-r...

https://www.rtl-sdr.com/kiwisdr-tdoa-direction-finding-now-f...

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With synchronized receivers you could do some rudimentary direction finding. Note that synchronizing SDRs is much more achievable if they're physically nearby (e.g. can run a cable between them for a common clock) vs if they're physically distant observers (can't exactly use GPS time for synchronization if you're measuring GPS interference)

> can't exactly use GPS time for synchronization if you're measuring GPS interference

Can other GNSSes (Galileo/BeiDou/GLONASS/etc) give usable timestamps? Seems like it'd be tricky for a jammer to target all of them simultaneously. (Of course, since they'd be on a different band, unless your SDR is wideband enough you'd need two RX heads which gives you potential issues with phase drift between the tuning VCOs even if your sampling is coherent).

Perhaps a sufficiently directional antenna/phased array (for getting an actual satellite signal) as well as an omnidirectional one (for picking up the jamming signal) could get you somewhere...

Or perhaps one could look at computing AoA at each receiver site (using MIMO-y techniques, e.g. Kraken/KerberosSDR) and triangulating based on angles instead, which wouldn't require synchronizing physically-distant sites at all...

The problem definitely seems soluble, though I don't have the technical background to know how realistic that is.

>> Can other GNSS give usable timestamps? Seems like it'd be tricky for a jammer to target all of them

Actually the opposite; GNSS systems are all purposely designed to operate at virtually the same frequency (check out this figure [1]) while cleverly not interfering with each other. There are sub-bands within each constellation too (L1,L2,L5 etc) but it's very easy to pump out wideband noise across all the GNSS bands.

[1] https://www.researchgate.net/figure/The-spectrum-of-current-...

Very helpful (as well as sibling comment by pierat). Thank you both. I will need to do some research with regards to pairing SDRs with local disciplined clock that can tolerate temporary loss of remote (stratum-0,1) time precision.

https://en.wikipedia.org/wiki/GPS_disciplined_oscillator

You can get rough areas with a GPS and a RTLSDR and a bunch of samples (either over time OR with lots of people with the same device)

But to get fine granular data, you need a timestamping SDR. (each parcel of signal data for a quantum of data needs an exact time down to 6-8 significant figures, basically GPS timebase).

Most your cheaper SDRs cant do that.

Stuff like the BladeRF and higher do provide timestamped data.

KrakenSDR would do a good job of this, they combine five RTLSDR into a coherent array. The top end of their tuning range is 1766 MHz which would include the 1575 MHz of the GPS L1 signal.

The little five antenna array can even attach on the roof of a car for a handy ground plane. Prob not a good idea to drive with it out there tho.

You could also use a single receiver with a small antenna array (GPS wavelength is around 20 cm) to estimate the angle of arrival of the incoming signals.

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