I always wonder how telecommunication masts operate. Some have very huge dishes that look like drums. What’s the function of these drums?
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Those drums are microwave dishes for point to point microwave links. They typically go from tower to tower, sometimes many tens of miles away. You may see thick cables going from the dishes down to the building at the base of the tower. That building houses all the radios, batteries and sometimes the backup generator for the site.
The dish looks like a soup bowl and the flat “drum” part is a cover to protect the feedhorn from the weather, bird nests. Also provides places for bees to make nests and squirrels to store nuts.
The mast is just to raise the antennas higher above the ground. Usually so that they can see further over the horizon as radio communications generally require line of sight. There are a number of different types of antennas which can be installed in the mast, often multiple are used for different things.
Some are variants of straight wires, similar to a radio whip antenna. These are omnidirectional antennas which works equally well in all directions. So it does not matter where the other end of the radio link happens to be. However the power from these antennas are not as good as it gets sent out in all directions. These are mostly used for broadcasts for radio or TV, or by relays for handheld radios used by emergency services, contractors, etc.
You also tend to see patch antennas. These looks like a flat board, especially with its protective cover on. But have various slots and wires in its structure. These antennas work in a specific direction. Usually 90, 60 or even 45 degree cones in front of the antenna. They provide more power then an omnidirectional antenna but only works if the other end is in front of it. These are typically used for cell phone towers and tend to be mounted in clusters with each antenna pointing a different direction covering all the sectors. One antenna can talk to a cell phone on one side of the tower while another antenna can talk to another cell phone without these talking over each other. So you can improve bandwidth over other technologies.
The dishes you mention are parabolic antennas. These might also have protective covers over them and look like short tubes instead. Parabolic antennas are extremely directional and can only work when pointing directly at the other end of the radio transmission. However they can send a lot of power so the signal is extremely strong. This allows them to maintain high bandwidths over long distances. They tend to be used for links between two towers instead of having to run a dedicated fiber optic line between them.
Point to point microwave link. Two drums on two towers have their flat parts pointing at each other. This type of communication isn’t for cell phones as the strength of that type of signal drops off very fast if you aren’t right in between those two dishes. Instead, these towers often have cell phone antennas as well (usually three tall rectangles on the pole) and use the microwave link to get all the phone calls back to the rest of the world. Microwave links are often used instead of wires in remote locations.
The drums are just directional antennas with a cover over the dish. The cover is transparent to radio frequency (RF) energy, but protects the dish and the antenna from the weather.
The dishes used with the antenna focus the RF energy so instead of a broadcast, they become a tight beam, kind of like the difference between a light bulb and a flash light. With all of the energy focused like that, the range of the signal they send is a hell of a lot longer than it would be if they just put an open-air antenna up, and it’s a lot more secure, too (you’d need to get an antenna in the beam path itself to intercept whatever was being sent)
The function of these dishes is to transport large amounts of data from one point to another over long distances. It’s a *lot* cheaper and easier to do this over the air than it is to try and run cables over several miles.
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