Comments by "SeanBZA" (@SeanBZA) on "Scott Manley" channel.

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  37. As more satellites were added in different orbits, accuracy improved. With low numbers of satellites, and also with long paths through the air to provide diffraction of the signal, you got poor accuracy. More orbits meant more visible at any time, and thus a more precise position. You need, IIRC, at least 4 to get a coarse position in 3 axes, and with every added satellite visible at the same time your error reduces. At 6 you get 100m, and with more the error reduces further, with most receivers able to handle up to 12 simultaneous decodes at a time, and with more sophisticated receivers using ADC units that can sample at the actual chirp bit rate, timing each individual bit as it comes in, and thus being able to correct for smaller drift with each cycle. Some of the software defined units have no real limit on the number of satellites they can view simultaneously, just depends on the amount of memory and processor speed, as you can always add more of both, and make the rake receiver scale with visible satellite numbers. Some of those have impressive cold start capability, being able to start from cold within a few minutes, and with warm start capability of seconds, provided the data they have is not too stale. Big issue is with noise, you find that often GPS signals in urban areas are poor, lots of RF noise desensitising the receiver, and also urban canyons making for lots of multipath distortion, and limiting visible sky to use. Sometimes I need to restart the old Garmin I have a few times, as it is unable to start, but often during RF quiet times it will be up and running in 2 minutes, from a warm start.
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