Originally posted by Oblivian
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The pool servers are generally stratum 2/3 servers (some strat 1). That means they are between 1 and 3 steps away from an original time source (GPS/PPS/Atomic). They will generally have 1 or more ms difference from a true time source (my S2 server seems to be mostly within +/- 1ms, but can occasionally be up to 5ms out for example. But, that true time IS the GPS time the other poster was referring to. There aren't different idea of "true" time.
The other poster has set up a stratum 1 server. This means they are generally going to be within 1ms (and depending on a variety of circumstances, considerably better than that) of actual GPS time.
I think that maybe you're assuming there's a constant "added" latency to true time that all users of the same pools will get. This is just not true. NTP tries to account for your latency by using multiple NTP servers (if you set it up thus) measuring latency as best it can and trying to work out the overall "closest" to the original time sources it can get. That difference will be + and - to the original time and different for everyone. Even if all people used the same time servers.
However, the user using the GPS time source is going to have a much more reliable time source on their local LAN and as such can provide much more reliable values for MLAT data.
I think there's a catch here though. It's much more likely that having a +/- 1ms time source matters little when the stream of data coming from the SDR dongle likely has an unknown and possibly variable delay. So, it can all be quite moot.
As I understand it, multilateration is more about using other signals of KNOWN location in order to get a temporal inference, rather than relying on home users being able to get the nanosecond accuracy needed for multilateration without known references.
However, I won't stake my life on that, since this latter point is moving into an area of my own relative ignorance.
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