Definition - RF Cafe Forums

RF Cafe Forums closed its virtual doors in late 2012 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2012, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts. Here is the full original RF Cafe Forums on Archive.org

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Antonio

Post subject: Definition Posted: Mon Nov 05, 2007 6:42 pm

Captain

Joined: Sat Jun 16, 2007 12:26 am

Posts: 12

Can anyone please define in detail about these???

1) What is the selectivity of a filter?

2) What is the mathematical expression for selectivity?

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jaslovkel

Post subject: Posted: Tue Nov 06, 2007 11:57 am

Captain

Joined: Tue Jun 26, 2007 10:27 am

Posts: 11

Location: Dallas, TX

Hi Antonio,

Selectivity is usually another name for how much attenuation is available in the stopband of a filter in a given frequency range. It depends on what type of filter it is to what the mathematical representation will be. This is because different filter approximations will have different transfer functions. However, the more poles in the transfer function will make the resulting circuit act as the ideal 'brick wall'. A narrowband system will require a filter with very high selectivity while a wideband system will require a low selectivity.

-J

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Antonio

Post subject: Posted: Fri Nov 09, 2007 3:31 am

Captain

Joined: Sat Jun 16, 2007 12:26 am

Posts: 12

Thank you very much for your help.

Posted  11/12/2012