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McMurry
Joined: 16 Feb 2008
Posts: 74
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 25 Jul 2008 15:58 low pass or band pass |
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just need a confirmation.
is this a low pass or band pass filter?
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LvW
Joined: 07 May 2008
Posts: 793
Helped: 151
Location: Germany
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| 25 Jul 2008 16:41 Re: low pass or band pass |
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It is neither a bandpass nor a lowpass, but a bandstop or notch.
(Assuming that the transfer function is shown rather than the attenuation function)
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RF-OM
Joined: 03 Aug 2007
Posts: 607
Helped: 113
Location: The Earth
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| 25 Jul 2008 17:34 Re: low pass or band pass |
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| It is bandstop.
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McMurry
Joined: 16 Feb 2008
Posts: 74
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| 26 Jul 2008 10:27 low pass or band pass |
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wow. luckily i did ask. =)
anyway, for notch filter, the cutoff freq. is found with similar way like normal filter?
i.e. just check the frequency value at -3dB ?
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LvW
Joined: 07 May 2008
Posts: 793
Helped: 151
Location: Germany
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| 26 Jul 2008 10:53 Re: low pass or band pass |
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| McMurry wrote: |
anyway, for notch filter, the cutoff freq. is found with similar way like normal filter?
i.e. just check the frequency value at -3dB ? |
Yes, 3 dB below the value at ω=0.
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McMurry
Joined: 16 Feb 2008
Posts: 74
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| 26 Jul 2008 11:09 low pass or band pass |
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| thanks =)
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LvW
Joined: 07 May 2008
Posts: 793
Helped: 151
Location: Germany
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| 26 Jul 2008 12:08 Re: low pass or band pass |
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But you should know that in most cases the 3-dB-bandwidth is less interesting since the notch filter is mostly applied to supress only one spurious frequency.
That means, the specification could be for example: attenuate fz by at least 60 dB.
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RF-OM
Joined: 03 Aug 2007
Posts: 607
Helped: 113
Location: The Earth
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| 26 Jul 2008 17:28 Re: low pass or band pass |
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| Yes, we usually interested in one frequency or narrow area around it. However, there is one important point: around this central frequency of bandstop filter group delay variations are huge and must be accounted.
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FANT
Joined: 27 Feb 2002
Posts: 337
Helped: 10
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| 26 Jul 2008 22:44 Re: low pass or band pass |
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It's a bandstop filter; don't look real due the 100 dB attenuation, but only a simulation.
Also the large bandwidth is very strange, usually bandstop are quite narrow.
This for my experience.
Mandi
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bilal_oct
Joined: 08 Aug 2008
Posts: 8
Helped: 1
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| 11 Aug 2008 9:46 Re: low pass or band pass |
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| I am sure it is a low pass, because it supress the high frequency components of the signal at the pi.
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LvW
Joined: 07 May 2008
Posts: 793
Helped: 151
Location: Germany
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| 11 Aug 2008 21:08 Re: low pass or band pass |
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| Do you know that there is a difference between low pass and band stop response ?
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jetset
Joined: 17 Jun 2004
Posts: 145
Helped: 10
Location: Panama
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| 19 Aug 2008 16:30 Re: low pass or band pass |
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| If the sampling frequency is 2π then you can only use the (0,π) band, in this case this is low pass filter, you can notice because the the (π,2π) band is a mirror of the (0,π).
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