6 ms·

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 FOS

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 2mo ago
Have you done that?
- londons_explore 2mo ago
  I have. It works. Used a huge amount of compute though and takes a long time to get a fix.
  - inigyou 2mo ago
    Maybe that's why nobody else does
    - rescbr 2mo ago
      You can use a FPGA, like this 2013 project: http://www.aholme.co.uk/GPS/Main.htm http://www.aholme.co.uk/GPS/Main.htm Or go old school (1991-1992): https://lea.hamradio.si/~s53mv/navsats/theory.html https://lea.hamradio.si/~s53mv/navsats/theory.html So yeah, this regulation is absolutely an inconvenient measure.
      - inigyou 2mo ago
        Have you done that?
        rescbr 2mo 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 2mo 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-with-a-hackrf-and-1-2m-satellite-dish/ 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/Nichols_ION_GNSS_2022.pdf 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 2mo 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/Nichols_ION_GNSS_2022.pdf https://radionavlab.ae.utexas.edu/wp-content/uploads/2022/10...
    - londons_explore 2mo ago
      Nearly all commercial GPS receivers use a 1 bit ADC. Ie. Just a comparator. The sample rate isn't high either - 16Mhz IIRC.

inigyou 2mo ago

Have you done that?

londons_explore 2mo ago
I have. It works. Used a huge amount of compute though and takes a long time to get a fix.
- inigyou 2mo ago
  Maybe that's why nobody else does
  - rescbr 2mo ago
    You can use a FPGA, like this 2013 project: http://www.aholme.co.uk/GPS/Main.htm http://www.aholme.co.uk/GPS/Main.htm Or go old school (1991-1992): https://lea.hamradio.si/~s53mv/navsats/theory.html https://lea.hamradio.si/~s53mv/navsats/theory.html So yeah, this regulation is absolutely an inconvenient measure.
    - inigyou 2mo ago
      Have you done that?
      - rescbr 2mo 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 2mo 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-with-a-hackrf-and-1-2m-satellite-dish/ 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/Nichols_ION_GNSS_2022.pdf 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 2mo 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/Nichols_ION_GNSS_2022.pdf https://radionavlab.ae.utexas.edu/wp-content/uploads/2022/10...
  - londons_explore 2mo ago
    Nearly all commercial GPS receivers use a 1 bit ADC. Ie. Just a comparator. The sample rate isn't high either - 16Mhz IIRC.