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GPS: BAD subframe = 0

In the log I now see quite a few entries as above. The last digit is either 0, 6 or 7. What does this mean?

Comments

  • There are 5 different types of GPS subframes. Hence the subframe blocks marked 1-5 on the GPS tab of the admin page. If a received subframe identifier is outside of that range I currently print the "bad subframe" message instead of silently ignoring it. There is some parity checking to help bad data bits from noisy channels being interpreted as good subframes. But parity can only do so much. It is not an error correcting code.


  • OK, so this does not indicate a GPS problem, just noisy channels with bit errors.
  • Yes. If you have a marginal channel you should also be seeing the "P" (parity err) indicator flashing red on the GPS tab. "U" means loop unlocked although this can occur briefly without causing any problems.

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