Q) Where is an RF preamplifier installed?
A) Between the antenna and receiver
The RF preamplifier is used to boost the received signals. This is useful to overcome significant signal loss due to long coaxial cable runs from the antenna to the receiver. Signal loss on coaxial cable can be a problem on UHF and VHF frequencies.
Antennta --> RF Preamplifier --> Receiver
For an example, check out the Hamtronics receiver preamp for VHF and UHF ham applications.