Band filters

Band filters (BF).
BF is a frequency-selection device that lets radio signals pass in a certain frequency range and stops them in other frequencies.
Generally, every passband filter is a BF, but we shall name BF those filters that pass radio signals in a more wide frequency range than a TV channel width.
BFs may be divided into three types: low-pass filters (LPF), high-pass filters (HPF) and passband filters (PBF).

Low-Pass Filter is a filter that lets radio signals pass if their frequency is below the cutoff frequency fcut (see Fig.1а) and stops radio signals with the frequency above fcut.

          
                     
                            a)                                                b)                                           c)
Fig.1. Standard amplitude-frequency response of LPF (a), HPF (b) and PBF (c).

High-Pass Filter is a filter that lets radio signals pass if their frequency is above the cutoff frequency fcut (see Fig.1b) and stops radio signals with the frequency below fcut.

Pass-Band Filter is a filter that lets radio signals pass if their frequency lays between fcut 1 and fcut 2  (see Fig.1c) and stops radio signals with frequencies below fcut 1 and above fcut 2.
Application domain. Usually, Band Filters are used in community TV reception systems for signal injection to the line from several receiving antennas (see Fig.2). It is required for clearing the output signal of a receiving band antenna from induced radio signals of other frequencies. Often, a single arrangement combines several Band Filters (e.g., LPF, PBF and HPF) with summation units (marked as  at Fig.2).

     
                    
Fig.2. An example of Band Filters application for establishing TV-reception from several band antennas.