Preselector
Encyclopedia
A preselector is a radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

 technological term for an electronic device
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 that is inserted between the antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

 and the receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...

, limiting the range of frequencies
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...

 that can be applied to it. Tuning to the desired frequency keeps the preselector's narrow bandwidth centered at the operating frequency, rejecting or reducing out-of-band unwanted interference signals. A preselector also protects the sensitive receiver input from damage caused by static and voltage transient. It improves the performance of nearly any receiver, but is especially helpful to those with broadband front-ends that are prone to overload, such as scanners or average receivers.

Extra filtering is needed because the front of the receivers, conformed by the RF power amplifier
Rf power amplifier
An RF power amplifier is a type of electronic amplifier used to convert a low-power radio-frequency signal into a larger signal of significant power, typically for driving the antenna of a transmitter...

s and mixer
Mixing console
In professional audio, a mixing console, or audio mixer, also called a sound board, mixing desk, or mixer is an electronic device for combining , routing, and changing the level, timbre and/or dynamics of audio signals. A mixer can mix analog or digital signals, depending on the type of mixer...

, have a limited dynamic range. Dynamic range
Dynamic range
Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity, such as in sound and light. It is measured as a ratio, or as a base-10 or base-2 logarithmic value.-Dynamic range and human perception:The human senses of sight and...

is defined as the amount of RF energy those circuits can handle without overloading. If the front-end overloads, the performance of the receiver is severely reduced or even damaged. In situations with noisy and crowded bands, or where there are strong local stations, the dynamic range of the receiver can quickly be exceeded. Extra filtering limits frequency and power that are applied to the receiver, allowing them to handle the overall dynamic range of signals that are within the desired band.

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