Why does a cell tower need to be massive to transmit data to a smartphone but the phone’s extremely small antenna can transmit data back over the same distance?
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Size of an antenna is correlated to how loudly it can transmit and how quiet of a signal it can receive.
Imagine a cellphone is your hearing-impaired grandma with laryngitis. If you want to have a conversation, with her, you have two options: get close enough for you two to hear each other, or get a loud enough voice and big enough ears to converse at your current distance.
A cell tower obviously can’t move and so has to just have a loud “mouth” and big “ears.”
To simplify it a bit, range is basically sqrt(Size1xSize2).
If you halve the size of one antenna the other needs to double to maintain the same signal between the two.
So since we can make the phone antenna/transmitter less powerful and sensitive in exchange for making the tower more powerful and sensitive we go with small phones and big towers. It keeps the big expensive parts on the tower, and phones small and with lots of battery life.
Note “Size” really doesn’t translate directly to physical size, it’s more about antenna directionality/gain + transmit power, and fancy hardware to do stuff like beamforming. But in general using large arrays of antennas, or stuff like a dish require more physical space so it’s close enough.
However if you look at a tower the physical antennas (on common cell phone towers the vertical rectangles up top attached to a triangle frame) , while much large than a phone, aren’t actually that big compared to the tower. The tower itself is used to get the antenna off the ground to keep line of sight between phones and the towers, since it’s really inconvenient to ask you to climb to the roof of the building to make a call 😀
A lot of people have mentioned that having a large cell tower allows for smaller phone antennas, but one thing I haven’t seen mentioned is that cell towers also need to include equipment for separating and routing a large volume of individual signals.
Edit more in keeping with eli5: A phone only has to process a handful of signals at a time, a cell tower has to handle thousands, and needs special equipment to do that.
Part of it is height. At those frequencies, it’s line-of-sight. Think of it like a lighthouse or beacon. The higher it is, the less likely it will be blocked by terrain, and the further it will go before it hits the horizon / curve of the earth.
A lot of people have mentioned that having a large cell tower allows for smaller phone antennas, but one thing I haven’t seen mentioned is that cell towers also need to include equipment for separating and routing a large volume of individual signals.
Edit more in keeping with eli5: A phone only has to process a handful of signals at a time, a cell tower has to handle thousands, and needs special equipment to do that.
Part of it is height. At those frequencies, it’s line-of-sight. Think of it like a lighthouse or beacon. The higher it is, the less likely it will be blocked by terrain, and the further it will go before it hits the horizon / curve of the earth.
A cell tower will be talking to several dozen or even hundreds of phones at the same time, a phone is only talking to one cell tower, so the tower needs much more bandwidth than any individual phone
A cell tower will be talking to several dozen or even hundreds of phones at the same time, a phone is only talking to one cell tower, so the tower needs much more bandwidth than any individual phone
Simply said, tower its transceiver and because it’s so massive it can not only transmit but also receive signals much more reliably.
Simply said, tower its transceiver and because it’s so massive it can not only transmit but also receive signals much more reliably.
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