Band-Elimination Filter

A band-elimination filter prevents a receiving unit from recognising a specific range of frequencies.

Such filters find wide application in satellite receivers operating in the C Band; this band is a range of frequencies between 4 and 8 MHz, historically used by long range satellite broadcasts, specifically TV and radio stations. Its primary benefit was that it made a large range of stations available to users with C Band satellite dishes.

However, in recent years, traffic has been added to this band, particularly from radar and WiMAX installations. Studies have shown that a fixed WiMAX transmitter can potentially cause interference with C Band frequencies within a 12 km radius. This potential disruption to the quality of a satellite television signal has necessitated the introduction of a specific type of Band Pass filter – the C Band Interference Filter for Satellite.

This device is a band pass filter that allows predefined signals, in this case certain pre-defined C Band frequencies, to pass through, while blocking any other signals. The interference filter is set to only pass through a tight and specific range of C Band frequencies. The C Band frequencies most often used by WiMAX and radar are explicitly attenuated.

Both active and passive band pass filters are available. The C-band filter is usually a passive type which does not require an external power source, and usually comprises only passive components like capacitors and inductors. Active filters, needing an external power source, are usually utilised in highly specific cases.