Hello all!!! Have you ever gone to a metro station or tunnel and wondered why I am not having signal in my phone? Today we are gonna dig the reason out.
Mobile phones uses high frequency signals. These signals will be blocked by thick concrete and steel. The tunnel or underground path will be made of thick concrete and steel. This will block the high frequency signals entering inside. So the phone signals will not be received in underground tunnels.
This is the reason why you can receive AM(Amplitude Modulation) waves inside the tunnel but not the FM(Frequency Modulation) signal.
In some underground metro stations like Delhi Metro, Hong Kong, you will be still getting mobile signal. This is because they use leaky feeder system in the tunnel.
Leaky Feeder System
Leaky feeder system is the thick cable laid in parallel inside the tunnel. These cables will be having holes or gaps. As the name suggests it will leak the signals.
The signal which the phone transmits and the signal received by the phone are also be carried by these cables. Since it is leaking the signals in-between, we need to provide boosters every 350 meters to boost up the signal and transmit the whole tunnel length.
Repeater
Another system used by some stations are the repeater. A repeater is same as the cell phone tower. We can have miniature cell phone tower(repeater) in the station.
The repeater receives signals from the phone towers and retransmits the signals. This will allow the signals to enter the underground station. But we need more number of repeaters to achieve the total coverage of the tunnel.
So, for underground communication leaky feeder system is the suggested one.
Thanks for reading. If you find this article helpful share with your friends. Have a nice day.
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