BTW, anyone have any info on the radiation pattern of the internal antenna?
Rúben Em Seg, Julho 6, 2009 13:31, Helge Hafting escreveu: > 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 > -- Rúben Leote Mendes -- ru...@netureza.pt _______________________________________________ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community