Base stations are low-power multi-channel two-way radios which are in a fixed location. They are typically used by low-power single-channel, two-way radios such as Mobile phone and portable phones. When you talk on such a mobile phone, you (and perhaps dozens of other people around you) are talking to a nearby base station. From that base station your phone call is connected into the regular land-line phone system by the mobile phone network. In the case of a portable phone, the connection is typically direct to a land line.
Because mobile phones and their base stations are two-way radios, they produce radio-frequency (RF) radiation (that's how they communicate), and they expose people near them to RF radiation giving concerns about mobile phone radiation and health. However, because both the phones and the base stations are low power (short range), the RF radiation exposure levels from them are generally very low.
The consensus of the scientific community, both in the US and internationally, is that the power from these mobile phone base station antennas is far too low to produce health hazards as long as people are kept away from direct access to the antennas.
It is critical to be aware of the difference between antennas, the objects that produce RF radiation; and towers or masts, the structures that the antennas are placed on. It is the antennas that people need to keep their distance from, not the towers that hold the antennas.
It is also important to be aware that there are many different designs of mobile phone base stations that vary widely in their power, their characteristics, and their potential for exposing people to RF radiation.