narrowband filter design

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From: Nick Foster (zaphod@coe.neu.edu)
Date: Thu Mar 20 2003 - 20:44:21 CST


Hey gang,

I'm trying to design a narrowband filter for a project of mine -- I'm
creating a magnetometer, to be towed behind a boat. The frequency of
interest is around 2130Hz, with a bandwidth of around 200-300Hz.

In practice, each measurement will have a single, fixed frequency. So,
I can use a very very narrow filter on it. However, I don't know before
I make the measurement what frequency it will be filtering on! An
active filter is therefore pretty nice.

Maxim makes the MAX260, a microprocessor-controlled active filter that
looks pretty good, but pretty old. Has anyone used this filter for
their projects, and had success with it? The idea would be to set it to
a wide bandpass, take an initial measurement of the frequency of
interest, and then "zoom in" on the signal by narrowing the passband.

I'm also looking for a low-noise, fixed frequency filter for the front
end, to be placed right after a preamp. What do the best CW filters
use? I don't know much in the way of practical filter design, but boy
can I calculate filter coefficients. =P

--nick


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