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I can receive FM signal about 50km away from the transmitting station but I lose signal from cell towers in about few km (1-3km)

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closed as too broad by Dmitry Grigoryev, Nick Alexeev Sep 14 '18 at 19:43

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ Do you know what "power" is? \$\endgroup\$ – PlasmaHH Sep 13 '18 at 13:35
  • \$\begingroup\$ Yes. Do you mean FM RADIO transmitters use higher power than Cellphone towers? Isn't there a fixed limit set by FCC \$\endgroup\$ – ObsessionWithElectricity Sep 13 '18 at 13:42
  • \$\begingroup\$ probably and likely that limit is higher for the FM band than the G2/3/4/5 bands \$\endgroup\$ – PlasmaHH Sep 13 '18 at 13:45
  • \$\begingroup\$ You can also receive AM half way across the world. FM transmitters work in the KW range, Cellular phones use mW, so six orders of magnitude right there, without taking bandwidth into consideration. \$\endgroup\$ – Lior Bilia Sep 13 '18 at 14:09
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    \$\begingroup\$ There's no point your cellphone being able to receive signals from the tower if the tower can't receive its responses. Therefore, there's no point using the maximum possible power at the tower, as all would happen is phones would be able to receive its signal but not send anything back, plus nearby towers would become more likely to interfere with each other. Used power is a cost for the operators, so the towers use the lowest power that they can get away with. See electronics.stackexchange.com/questions/299889/… for details. \$\endgroup\$ – Jules Sep 13 '18 at 14:23
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There are likely more reasons, but consider your tiny hand held device only develops a fraction of a watt of transmitted power. Clearly, then, it is your device that has limited range. And if your device developed more power, then you would be "stepping" on other's signals in other cells normally outside of your range. If you are clear minded, you can easily see how this could reduce the number of simultaneous cell phone calls by orders of magnitude in a populated city.

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    \$\begingroup\$ Somebody on SE has very poor habit of downvoting aggressively on every post. \$\endgroup\$ – ObsessionWithElectricity Sep 15 '18 at 13:11
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There are several reasons:

    1. A cellular network is bidirectional. The base station needs to receive the signal of your mobile phone as well for the communication to work. It doesn't matter how much power you transmit with the base station if it can't hear the tiny transmitter in your phone. Mobile phone transmit power is in the order of 1W, while FM radio stations may transmit with multiple kilowatts of power.
    1. Higher frequencies are more directional. FM radio frequencies are around 100MHz while cellular frequencies are about one magnitude above that. This means you have more absorption in obstacles and the waves do not diffract (bend) around them as much as with lower frequencies.
    1. Larger receiver bandwidth means lower sensitivity, because the total noise floor is higher for a larger bandwidth. While an FM radio channel has a bandwidth of less than 100kHz, the bandwidth of GSM is 200kHz and for newer cellular standards even multiple megahertz.
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