-------- In message <sn1pr11mb10248e0077e3055b2286e92ece...@sn1pr11mb1024.namprd11.prod.outlook.com>, Mark Sims writes:
>The next thing I want to try is a receiver self-survey vs the post processed >results... I fell into that trap many years ago as well :-) The post processed result eliminates and compensates for a lot of effects which are invisible to the receiver, that is the entire point of post processing. But if your goal is to get good 1PPS out of your receiver, forcing it to hold a "perfect" position, means asking it to deal with effects it cannot measure, and as a result you get *worse* 1PPS performance than if you use the "wrong" self-survey position. That said, there are certainly a lot of issues with how the self-survey position should be calculated *and* maintained, because it really needs to change over time for optimal performance. Almost any suboptimal antenna-position means that you should vary the position-hold coordinates over the orbital period (but see below), but over longer periods also environmental factors come into play. For instance if you put the antenna on a wood-construction, be it a pole or a house, it coordinates will vary at the cm level over the seasons as the wood expands and contracts. The good news is that the receiver gives you the input data to work and model these biases, the bad news you don't get a lot of data. I did some experiments when ten Oncore M12+T's passed through my lab many years ago: I plotted the reported "residuals" vs. satellite position, and I tried to update the held position on a daily basis using the trend, and the results were measurable at the several ns level: http://phk.freebsd.dk/raga/sneak/ I didn't persue this further, because my latitude is particular unfavourable to the simple (N/S+E/W) approach (no birds north of me) and with only a single receiver the amount of input data is too low for such a crude algorithm. A more complex geometrical model could probably get more mileage out of the sparse data, as would tracking more birds than the 12 the M12 could track. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.