Preamplifiers or preamps are low noise amplifiers (amplifies signal but not noise) that mount to (or close to) an indoor or outdoor antenna to improve a weak signal. Most preamps are 2 piece units, an amplifier mounted close to the antenna, and a power unit inside the home that supplies power to the amplifier through the coax cable. The closer the amplifier unit is to the antenna, the greater the signal improvement. Signal improvement is the preamp gain minus the Noise Figure minus cable loss between the antenna and amplifier unit. The lower the noise figure (NF), the better. Signal improvement can be 15 to 20 dB or more, significant. Some antennas have a built-in preamp to maximize performance.
The power unit uses standard house current (110 Vac), some can also get power from a USB connection. The power unit supplies direct current (DC) power to the amplifier through the coax cable center conductor. There can only be cable between the preamp and the power unit, no splitters/combiners or impedance matchers. Coax ground blocks (for lightning and static protection) and cable connectors can be used if they pass DC power (most do).
Preamps come with either a fixed gain or an adjustable gain, most cover the VHF and UHF bands, some are indoor only, some can be mounted outside. Some preamps have an FM Trap (switch) to filter out the commercial FM radio band which is between RF channels 6 and 7. The filter may be needed if an FM signal is strong enough to overpower the preamp or reduce it's automatic gain control. Some FM traps reduce RF channel 6 reception.
BOOSTER AND DISTRIBUTION AMPLIFIERS
Long cable runs and signal splitters may require installing a booster amplifier or a distribution amplifier. A booster amp has a single high gain output (30+ dB), some are fixed gain, some adjustable. A distribution amp has multiple outputs (built-in splitters), each output has a fixed gain of 3 to 8+ dB. A booster or distribution amp will not improve a weak antenna signal, because it amplifies signal and noise, but it will allow for longer cable runs and device connections. The amplifiers use standard house current (110 Vac).
A signal that is too strong can overwhelm (saturate) a TV receiver, causing signal distortion (cannot decode signal). An attenuator can reduce the signal to an acceptable level. Some attenuators have a fixed reduction, some are adjustable.
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