What type of device is commonly used to increase signal strength in a radio?

An amplifier is a device specifically designed to increase the strength of a signal. In the context of radio communication, it takes a weak input signal and boosts it to a higher power level, making it more suitable for transmission or further processing. This amplification is crucial for ensuring that the radio signal can cover greater distances or penetrate through obstacles, thereby improving the overall performance and reliability of communication.

In contrast, a modulator would be responsible for altering the characteristics of the radio signal (like frequency or amplitude) to encode information, but it does not inherently boost signal strength. A resistor is a passive component that can reduce the signal strength by limiting current flow, which is the opposite of amplification. An oscillator generates signals but does not amplify existing signals. Therefore, the amplifier is the appropriate choice when discussing devices that enhance signal strength in radios.