A Radio Repeater is a device that boosts communication range.
Repeaters receive a weak signal and retransmit it.
By retransmitting the signal at a higher power, further range is enabled.
Another reason to use repeaters, is obstacles.
Obstacles include both natural and manmade structures.
Examples of natural obstacles include hills and mountains.
Examples of mademade obstacles include buildings and bridges.
Obstacles matter to radio signals.
Basically they block or attenuate radio signals.
Attenuation means reduces the power of the signal.
Reducing the power of the signal, reduces communications range.
A classic use of a radio repeater is to overcome a hill.
Hills will block radio signals above 30 MHz.
Radio signals above 30Mhz are normally known as ‘line of sight’.
The term ‘line of sight’ is slightly misleading, as signals will pass through a building.
Therefore you don’t actually have to be able to see a clear path between transmitting and receiving radio.
However hills block radio waves, so a hilltop repeater overcomes this.
Placing a repeater on a hill allows signals to be received from one side of the hill, and boosted to both sides of the hill.
This is because the repeater antenna is physically above the top of the hill.