1) Radio electronic 
A preselector is a radio technological term for an electronic device that is inserted between the antenna and the receiver, limiting the range of frequencies 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 interferen....
a selector associated with a calling line for the purpose of connecting this line to a free outlet
a preamplifier between the antenna and receiving circuit, used to improve reception.