The higher the channel, the smaller the antenna. For example, the UHF antennas are smaller than VHF antennas because the channel frequency is higher.
Indoor antennas are generally small and designed to be placed on or near your TV set. Outdoor antennas are significantly larger and are made to go on your roof or in an attic.
Generally, the larger the antenna, the stronger the signal it will provide to the TV set.
Antennas can be affected by walls, fluorescent lights, computers, cordless phones, and even by people moving around in the room.
To help with the size disadvantages, you can use an electronic amplifier that will enhance the signal. The amplifier can be built in as it is in many indoor antennas or it can be a separate device that installs in between an outdoor antenna and the TV set.
You should only use an amplifier if you have to because an amplifier also amplifies noise along with the signal. This amplified noise can sometimes overpower the signal and can make your reception worse.