Filters

A filter is an electric circuit (often called a network) that allows certain frequencies to pass but rejects (attenuates) other unwanted frequencies.

In general, filters are one of three types - Lowpass, Highpass and Notch,

Filter Design

Low Pass Filter

A low pass filter is designed to pass low frequency signals and to block those above a certain design frequency. In ham radio these are typically used to block VHF harmonics of HF transmissions that interfere with TV reception.

High Pass Filter

High Pass filters allow the transmission of high frequency transmissions and block frequencies below the design frequency.

Band Pass Filters

Band Pass filters allow a specific band of frequencies to pass and block all those above and below. these are typically used in repeater instalations to "notch" the frequency of the repeater and reject all unwanted frequencies.

Band Stop Filters

These filters block specific bands and allow those above and below to pass.

Filter Types

Cavity Filter

LC filters

Saw Filter