narrow band-pass filter

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clcada@yahoo.co.uk - 10 Dec 2005 19:58 GMT

Hi,
I am really confused with something which is probably too basic for all
of you but ... I could really use your help.
I was checking out a computer program which allows you to specify the
parameters of any kind of signal going through any kind of system and
then provides you with the output.
I used a narrow bandpass filter in order to extract a single harmonic
from a pulse train with really narrow pulses. What I don't get is how
one should decide what bandwidth to use for the bandpass filter. Is the
fact that the pulses are very narrow or wide of any significance?

Thank you!

Erida

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salmonegg@sbcglobal.net - 10 Dec 2005 22:44 GMT

On 12/10/05 11:58 AM, in article
1134244734.653368.89340@g43g2000cwa.googlegroups.com, "clcada@yahoo.co.uk"

> Hi,
> I am really confused with something which is probably too basic for all
[quoted text clipped - 10 lines]
>
> Erida

If you make the bandwidth large compared to the prf, you will get more than
one harmonic through. If you make it too narrow, you will miss all the
harmonics unless you happen to tune onto one.

Bill

-- Ferme le Bush

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Noral Stewart - 11 Dec 2005 13:28 GMT

A band pass filter will simply measure the signal strength within the band
you define. In today's world, it is more common to use Fast Fourier
Transform (FFT) analysis to study the detailed frequency content of a
signal.

> Hi,
> I am really confused with something which is probably too basic for all
[quoted text clipped - 10 lines]
>
> Erida

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Mike Yarwood - 13 Dec 2005 00:07 GMT

>A band pass filter will simply measure the signal strength within the band
>you define. In today's world, it is more common to use Fast Fourier
>Transform (FFT) analysis to study the detailed frequency content of a
>signal.
>> Hi,

>> Is the fact that the pulses are very narrow or wide of any significance?

Not really - they just alter the zero frequency content - wide pulses in a
pulse train have narrow gaps and narrow pulses have wide gaps, it's where
the amplitude changes that most matters and it changes in the same places
whether the pulses are narrow or wide ( I'm assuming that these are
aproximately rectangular 'pulses' you are talking about - you can change a
pulse train with wide (+ve going) pulses into a pulse train with narrow
(-ve going) pulses just by shifting the DC ). If you look at the fft of some
of them as Noral Stewart suggests, you will see what he and Bill mean.

Best of Luck - Mike

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Natural Science Forum / Physics / Acoustics / December 2005

narrow band-pass filter