General Question

2davidc8's avatar

Why can cell phone signals penetrate buildings, but GPS cannot?

Asked by 2davidc8 (7762points) July 6th, 2017

I know that if you’re deep many floors in the basement, or in a cave, you can’t get cell phone access, either, but in general cell phone signals seem to have greater penetration. You can’t get GPS if you’re just among some tall trees.

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7 Answers

kritiper's avatar

Most likely has to do with the wavelength widths of the different signals.

Tropical_Willie's avatar

GPS signals use data plan not cellphone.

Lightlyseared's avatar

Line of sight and windows probably has more to do with it.

LuckyGuy's avatar

The GPS power level at the receiver is much lower. A typical GPS satellite has ~1,000 Watt solar array for power. It is transmitting at 500 Watts output on a few frequencies, so call it 100 Watts at the frequency of interest. The satellite altitude is about 12,500 miles with an average distance to receiver of about 15,000 miles. Power falls off with the square of the distance. The average cellular system is only about 1 mile from the receiving phone. They are supplied power from the grid which can easily provide 500 Watts to the transmitter if needed.
So all things being equal (even though they are not) the received signal from a GPS would be lower than 1/100,000,000 of the cellular signal.

2davidc8's avatar

Thank you for your answer, @LuckyGuy. I had thought it had more to do with wavelength or frequency.

LuckyGuy's avatar

There is some difference between the two frequencies. but the big one is received power.

There are mini GPS-like systems that use VHF signals broadcast from transponders on emergency vehicles. They can park outside a big building in several locations and make a constellation of transmitters that can be used to determine location anywhere in the building.
Clever. And handy.

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