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Twice this year, my car's GPS receiver got totally lost. It seemed the cause of this was heavy cloud, (because I can't think of any other reason), and the GPS stayed in "Recalculating" mode, until the clouds cleared.

I do know that some long distance van drivers carry GPS jammers, in order to elude their employer's tracking systems for short periods of time, but there were no vans or trucks on the motorway at the time, just very heavy cloud above me.

I wonder is there a physics based reason, (signal interference or to save satellite power, for example), why more power is not put into the transmission signal?

I ask this as a physics based question, I am not looking for a directly engineering or electronics based answer

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    $\begingroup$ This may well say more about the quality of your receiver than anything to do with the satellites. I've never lost a GPS signal except in cities, and I'm pretty sure the US military doesn't lose track of its position when it rains. $\endgroup$ – user10851 Aug 30 '15 at 18:30
  • $\begingroup$ @ChrisWhite That's a good point, it never happened with any other brand I owned, that's why it caught me by surprise. $\endgroup$ – user81619 Aug 30 '15 at 18:34
  • $\begingroup$ The restriction may be to avoid interfering with adjacent frequency bands. $\endgroup$ – Daniel Griscom Aug 31 '15 at 1:06
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Some facts - not a definitive answer:

A calculation of GPS power is given at this link and a more in depth analysis at this link. With about 1 kW available from the solar panels for most of the orbit, it seems that "available power" is not the limiting factor. The second link does imply that balancing the power from all satellites is important to ensure clean reception as

Each GNSS signal is a potential source of interference to other GNSS signals

But that implies that as long as all the satellites transmit at the same power, it doesn't matter so much what that power is. Currently it seems to be limited to about 50 W (but with the antenna gain, the "effective power" is a bit higher than that).

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  • $\begingroup$ I would accept this as an answer, I has completely forgotten the fact that if power was increased for all of the satellites, the interference problem may still remain. $\endgroup$ – user81619 Aug 31 '15 at 18:07

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