I get that our phones can pick up signals from towers since they have a much stronger signal and enough power for that. But what doesn’t make much sense to me is how our phones’ tiny antennas can still produce a signal strong enough to reach the tower as well and create a two-way connection. How is that possible? Does the tower just pick up weak signals and strongly amplify them?
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Think of the tower having really really sensitive ears. It can hear stuff that isn’t that powerful, there are lots of tricks and crazy physics that phones and towers use as well to help this. But towers at the end of the day are just really sensitive receivers. Its a lot easier to hear a faint signal (that is make a really good receiver) than you’d think, and your phone has actually enough power for that signal to go a few miles and still be heard.
The radio frequencies used by cell phones are strictly regulated by law. The cell carrier companies paid a ton of money to governments for private access to certain radio frequencies. The government has radio cops that make sure that no one else uses those frequencies – this ensures that cell phones get a clear path, without interference, to the tower. Wifi uses “free for all” frequencies, which can be used for anything – cordless phones, bluetooth, microwave ovens, baby monitors, all sorts of stuff – plus you may well have your neighbors wifi also using the same frequency your stuff wants to use. Because of all the stuff using these frequencies, there is a ton of interference.
Your typical cell phone transmits at either 0.6W or 3W. This is good for somewhere between 22 and 45 miles with no obstructions. Most cell zones have a radius (they’re not necessarily circular) of around 1.25 miles. So in urban environments where you are more likely to find obstructions you’re well within your phones range. Cell towers are on towers (ok it’s in the name) and/or at high elevations to reduce the number of obstructions and maximize the range.
Radio receivers work on VERY low power levels, but have great sensitivity. Your phone will be able to work with a received signal strength of around -120 dBm which is the equivalent of 1 femtowatt (1 x 10^-15 watts).
The GPS satellites transmit at “only” 25.4W and are 12550 miles away (if directly overhead which they usually are not).
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