On Mon, 21 Nov 2016 14:36:49 -0500 Bob Camp <kb...@n1k.org> wrote: > The reflection issue ahead of the antenna is a reflection of the signal from > a single satellite. The multipath > reflection makes that satellite appear to be further away than it really is. > In the case that the reflected > signal is *stronger* than the desired signal, the multipath reflection > “captures” the receiver and the net > solution is messed up.
Even a weaker reflected signal can cause significant change of the correlation peak and thus of the apparent distance of the satellite. The multipath error envolope diagrams are usually for multipath to direct path ratios of between 1:2 to 1:10 (mostly depending on what the author wants to show or how much he wants to cheat). > In the case of a mismatched cable, there is no “single satellite” issue. > Everything is impacted by the mismatch. > Even if the mismatch is pretty bad, the “primary” wave is the one that will > dominate at the receiver end. The > reflections will always be lower in amplitude. That effectively guarantees > that you don’t have a multipath > issue from the coax. As above, weaker signals can still cause quite a bit of change in the correlation peak, but in this case it will not matter because the reflection acts the same on all signals. I.e. the net result is a small time offset (but no position offset). Unfortunately, there is one big assumption in here that does not hold true: for all signals to be affected the same way by the reflection, the receiver must be exactly linear. But we know that many of the components in the signal path of the receiver are distinctly non-linear functions. So there is a slight change of the position (and thus time) due to reflections in the cable. But, as we are usually dealing with minute differences in impedance, the reflected signals are heavily attenuated. Assuming we have a nominally 50Ω -- Malek's Law: Any simple idea will be worded in the most complicated way. _______________________________________________ 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.