> Laws of physics
Ahhh, this is always a good start...
> That's why your phone can talk to base station a kilometer away, your WiFi will
> not carry over about 100m and bluetooth peripherals barely have 10m range.
With only very minor corrections, like the last 10 metres or so, all of these are due entirely to radiated power. The two corrections are near field effects, and building materials.
> 2. Meters long? AM receivers? What?
The limit for practical efficient antennas is about 1/4 wave. A 100 kHz AM signal is 3 km long. An efficient antenna for AM is about 750 meters long. The typical car antenna, at about a metre long, has a gain around -20 dB, around 1% efficiency. That is one of those "laws of physics" you claim to understand. The only reason you can hear anything on AM is because they broadcast tens of thousands of watts. Here, read something:
> Because GPS sends on wave length that is relatively clear from other signals and
> that is able to carry the weak signal over the necessary distance
No, it's because the quarter wave antenna at 1575 MHz is about 5 cm, which fits quite nicely in a cell phone. While a car AM antenna has a gain around -20 dB (and a Walkman is probably down around -25 or less due to the antenna being the earphone which isn't exactly straight), the typical cell phone GPS antenna has a gain around -9 to -2 dB.
Recall that dB is logarithmic; this represents and improvement of two orders of magnitude, meaning that the ~250W of radiated power from the GPS is received at about the same power density as 25kW from AM. Actually more because of the physics of AM:
There are minor adjustments throughout, but this is good to an order of mag, or better.
Really, you should make sure you know what you are actually talking about before you try to quote physics to the /. crowd.