On Mon, 12 Aug 2019 12:05:14 +0200 Adam Kumiszcza <[email protected]> wrote:
> I cannot see any difference between these positions. I've made 10 > measurement for each position, getting 12 SNR values for satellites for > each measurement and then calculated the average of these. > Hanging antenna had 25.18 SNR average (2.21 standard deviation). Antenna on > a ground plane had 26.10 SNR average (2.08 standard deviation). > https://docs.google.com/spreadsheets/d/1lvGFTQS62MqiQALjHmWFZRY3hb5O1OqANFGBhnCaEUo/edit?usp=sharing SNR is a bad indicator of multipath. Multipath changes the SNR by at most 3dB. And the change can go in either direction. For GPS L1 C/A the multipath can affect the timing solution by up to 30ns (IIRC, I don't have a reference at hand). That's much more than you'd expect from just a 3dB degradation, and definitely not what you would expect from a 3dB increase in signal strength. The reason for this is that the multipath signal is correlated with the signal and affects it differently than just random noise. If you want to see what the effect really is, you have to measure the output of your GPS to a more stable standard (at the very least a good rubidium vapor cell standard) and look at the variations with a tau up to 24h. Note that multipath is usually correlated on a 12h/24h basis, but it is not necessarily a strong correlation as the signal path changes slightly due to changing satellite orbit and changing lensing effects of the atmosphere. How much correlation you get depends on a lot of factors that are not easy to quantify in an uncontrolled environment. Attila Kinali -- <JaberWorky> The bad part of Zurich is where the degenerates throw DARK chocolate at you. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
