Band Reject / Notch Filters

Band Reject Filters and Notch Filters are often used in radio and measurement technology. They make it possible to filter out specific frequencies and eliminate unwanted interference. By precisely controlling the frequency ranges, they ensure high-quality and clear signals.

Wainwright Instruments offers high-quality filter solutions that effectively block unwanted frequencies in order to deliver a reliably clear signal transmission.

Differences between Band Reject Filters and Notch Filters

Although Band Reject Filters and Notch Filters perform similar functions, they differ in their bandwidth and application:

Band Reject Filters (also known as Band Stop Filters) are designed to block or attenuate a wide frequency band while allowing other frequencies to pass unhindered. They are often used to remove unwanted noise or interference from signals. These are, for example, noise or carrier signals from communication systems.

Notch filters, on the other hand, specialize in suppressing a narrow, specific bandwidth of frequencies, often around a single frequency. Typical applications include the removal of interfering frequencies such as 50 Hertz mains hum or specific feedback, while leaving the rest of the signal intact. An important parameter of notch filters is the quality factor (Q-factor). A high Q-factor enables precise suppression of a narrow frequency bandwidth, while a lower Q-factor provides broader suppression.

Function and installation of Band Reject and Notch Filters

A Notch Filter filters out certain frequencies through a combination of resistance, inductance and capacitance in an RLC network. Band Reject Filters use similar principles to block wider frequency ranges. A precise calculation of the filter structures and dimensions is required to ensure that the filter works efficiently, achieves the desired specifications and, in particular, effectively suppresses the desired frequencies.

Depending on the application, different filter technologies and filter types are used to eliminate the unwanted frequencies.

Manually and digitally adjustable
Band Reject Filters and Notch Filters

There are two main types of Band Reject and Notch Filters: manually adjustable and digitally adjustable filters. Both types have their advantages and are used in different areas depending on the application.

Manually adjustable filters

Manually adjustable Band Reject Filters and Notch Filters are set mechanically or using special controls. The user can set the desired frequency manually. Manual filters are particularly suitable for applications where the filter frequency only needs to be changed infrequently or where a very specific adjustment is required. They are often more robust and less prone to technical failures.

Digitally adjustable filters

Digitally adjustable Band Reject Filters and Notch Filters offer a flexible and dynamic way of suppressing frequencies. These types of filters are controlled by software or microcontrollers and allow frequencies to be changed in real time without manual intervention. They are ideal for applications where frequencies change frequently or when they need to be adjusted with particular precision. They also enable greater accuracy and automation.