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  • awesomeusername · 3 days ago

    Seems fairly useless to me, for a few dollars I can sample the L1 frequency with a dumb device which has no idea of speed or altitude, and do the calcs with FOSS which is in the wild.

    Basically a rule which inconveniences the honest and has zero impact on the bad dudes, whoever they are

    • inigyou · 3 days ago

      Have you done that?

      • londons_explore · 3 days ago

        I have. It works.

        Used a huge amount of compute though and takes a long time to get a fix.

        • inigyou · 3 days ago

          Maybe that's why nobody else does

            • inigyou · 3 days ago

              Have you done that?

              • rescbr · 3 days ago

                Nah, I live in a major city between two airports, under an airplane departure and a heli route. I can't really launch rockets or balloons from my home.

                When I was at uni I didn't have the funds for this hobby unfortunately.

            • minetest2048 · 3 days ago

              There's a strong indication that SpaceX does use software receiver in Falcon 9 and Starlink: when they didn't encrypt the downlink telemetry someone captured the signal and found some plain text: https://www.rtl-sdr.com/receiving-space-x-falcon-9-telemetry...

              That plain text looks like what a software GNSS receiver outputs as its very verbose, and this paper: https://radionavlab.ae.utexas.edu/wp-content/uploads/2022/10... , a paper about a software receiver mentioned this:

              > PpRx has been licensed through the Radionavigation Lab to multiple commercial companies, but notably a major aerospace company that uses the technology across their suite of advanced spacecraft and satellites. The SDR is deployed across the company’s mega-constellation of satellites used for broadband Internet

            • minetest2048 · 3 days ago

              For L1 I think a raspberry pi can have a reasonably fast time to first fix, for offline processing you can go faster than real time. L2/L5 need large sampling rate and a pi is probably not fast enough.. unless if you ditch float32 processing and do 2 bit signal processing, a uni commercialized that: https://radionavlab.ae.utexas.edu/wp-content/uploads/2022/10...

              • londons_explore · 3 days ago

                Nearly all commercial GPS receivers use a 1 bit ADC. Ie. Just a comparator.

                The sample rate isn't high either - 16Mhz IIRC.

        • AlphaWeaver · 3 days ago

          [2016]

            • angry_octet · 3 days ago

              It's important to note that this is in relation to real time position estimation. You can collect the signal measurements and process offline later for telemetry reconstruction.

              • holgerschurig · 3 days ago

                CoCom was terminated in 1994 and is entirely irrelevant by now (IANAL and all that)

                What we have now is https://en.wikipedia.org/wiki/Wassenaar_Arrangement

                Fun fact 1: Switzerland (a major provider of GPS chips via u-blox) never signed or ratified CoCom. But they still followed it mostly, for fear of retaliation. They even had an allowance of "sell list 1 goods for up to 35 million Schweizer Franken" that they never reached, they only went up to 8 million Schweizer Franken. They however are a member of Wassenaar.

                Fun fact 2: Russia is a member of Wassenaar. But I guess they now give a shit on it and give to North-Korea whatever NK wants, for all of these nice North Korean cannon fodder soldiers.