Radio System Filters

A filter device is that used to allow or stop selected frequencies, or eliminate (filter out) any unwanted signals. In more technical, an RF filter is designed to allow attenuation or transmission of range of frequencies that would be applied. For an example, an RF filter helps to cut out RF interference (generally noise) that could occur if a hairdryer or lamp or else any noisy device is activated. RF filter used in different scenarios as per the requirement. Normally, there are basic four types of RF filters available in market.

High pass filter – It allows only higher frequencies, this done by allocating a cut off frequency which has a value of low frequency that can be allowed. In description it attenuates any low frequency.

Low pass filter – It’s just the opposite of High pass filter, it allows all the frequency which is below cut off frequency, but it attenuates any frequency above cut off frequency.

Band pass filter – It will allow the frequency only between the selected ranges with no attenuation. Although it will attenuate above or below frequencies than the desire frequency range. Great examples for band pass filter are cavity filters, surface acoustic wave and crystal filters. As the picture below describe a combination of high and low will result in pass band frequency range.

Band stop (reject) filter – It will attenuate a frequency range by allowing all the other frequencies to pass without attenuated. In industry it worth to use band pass filter than a band reject filter.

Filtering plays a vital role in Cellular transmission and satellite communication etc. Filtering out unwanted signals will allow the transmission successful rate to be high. Which significantly allows SNR (Signal to noise ratio) to be high. In more detail if signal level is higher than the noise, message will be more clearly deliver to receiver. For example consider, in a house in one room a boy watching TV and in another room another boy listening to radio if they keep the door open, both sounds will clash and both of them cannot enjoy the shows. If they close the door and watch TV or listen to radio interference will be low content they wanted will be clearer. Same applies in RF communication when noise is high message won’t be clearer or sometimes it will be completely distorted. In order to avoid this type of loss of signal or distortion filter is used to avoid noise or any interference caused to the original message signal.