Tomasz Suchan wrote: > Hi Armin, > >> I use the atenna for GPS Tracking during biking and car tours. >> As the FR is always running (no sleep) and with activated GPS >> module - the battery last about 4h - then it's empty. > > Is accuracy much better with external antenna?
If the external antenna can be placed in a better location than the internal one - or if it gets better signal strength. An external antenna on the car roof may see more satellites than the FR sitting on the dashboard, because that metal roof block radio transmission. Now, the FR will see many satellites even inside a car, but those signals cannot penetrate directly through the roof. Some satellites will be seen directly through windows. Signals from the rest may bounce off the hood and come in through windows, or diffract (bend) around the roof edge. Such redirected signals are weaker, and they give greater position error. The latter because they really give the position where your FR would have been, _if_ the signal had not been diffracted or reflected. The GPS receiver is smart, and will discard data from satellites that seem to disagree with the rest. But there are two problems with this: * An extra satellite that gets discarded no longer helps improving accuracy. * If two groups of satellites seems to disagree on position, then the receiver could lock onto the wrong group for a while. An external antenna see all the satellites directly, and don't suffer such problems. Unless you are near tall buildings or mountainsides, which cause the same kind of problems. So an external antenna is great if you have a roof above you. Such as in a car or boat. The problems above don't happen on a bike. Still, an external antenna might help, it may be bigger/better than the internal antenna and get more from a weak signal. For example, if you move around in heavy rain in a forest. Helge Hafting _______________________________________________ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community