In electronics, an antenna amplifier, also called antenna preamplifier, antenna preamp or antenna booster, is a device that amplifies an antenna signal, usually into an output with the same impedance as the input impedance. Typically 75 Ohm for coaxial cable and 300 Ohm for twin lead cable.
An antenna amplifier allows a weak radio signal to be detected, thus most devices that receive radio waves already have an RF amplifier stage in the front end that amplifies the antenna signal.
The best is to only use a amplifier as close to the antenna as possible with the highest gain in the area that you are interested in receiving (UHF) with the lowest possible noise and both at a reasonable cost.
The KEY is that you want a relative "good" level of input at your receiver (TV) with the minimum noise. A mast mounted amplifier (doesn't matter if it is called a amplifier or preamplifier) is the best when you are in a remote area. In theory it is best if you amplify a "clean" signal to a higher level than a "noisy" signal to a higher level. All cable has loss and the higher up that you go in frequency (VHF to UHF) the more loss that the cable has. If you start with a low level signal at the antenna and then butt it into coax cable, you are going to have less come out at the other end than went into it from the antenna. The amount of loss depends upon a number of factors, cable type and cable length are the two most important. Cable is rated in db loss per 100' at X MHz (frequency). RG-6 cable is the cable most used in TV use. Like all things there is good RG6 and not so good. as a example, Belden 1829AC Coax - Series 6 has a loss of 4db/100 feet at 500 MHz (TV Channel 18)- 495.250 Channel 32 which is 580 MHz, Channel 52 is 700 MHz a 5 db loss At TV channel 2, the cable would have a loss of 1.4db. So at channel 18 you would loose more than 1/2 the power in 100' of cable between the antenna and the TV.
A amplified indoor antenna does absolutely nothing for reception, since we all know that the only purpose of the amplifier is to overcome long lengths of wire and not to physically make the signal look larger.
Amplifiers amplify everything, Both the signal present at the antenna and the noise, both ambient background noise,(electric brush noise, gasoline engine ignition, electric fence,etc) the noise generated by the amplifier itself and all other electrical noise. When the level of noise is louder than the signal, you will have no signal.