Notice the difference between the two masts.
The white pole at the top of the mast on the
right is called a 'capping cylinder' and is
used to protect the dipoles inside the
transmitter from weather damage.
There are four dipoles for each channel
contained within the capping cylinder, to give
good multi-directional coverage.
The Channel 5 mast on the left employs newer
technologies that do away with the need for a
Some relays have separate capping cylinders
- this is for directional purposes.