filter slopes..

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filter slopes..

Post  holly87 on Sat Jan 26, 2013 5:33 am

Hi,
I am using your MEA1060-Up-BC standard (G=55, bandwidth 0.02 Hz-8.5 kHz) + FA60S-BC (G=20, bandwidth 10Hz - 3 kHz).
In the datasheet (http://www.multichannelsystems.com/sites/multichannelsystems.com/files/documents/data_sheets/MEA1060.pdf), I read that filter slopes are

MEA1060-BC-PA: 20 db/decade (high pass), 60 db/decade (low pass);
FA60S-BC: 20 db/decade (high pass), 80 db/decade (low pass);

Thus, I would expect that the frequency response gain has a slope of -140 dB/decade at high frequencies..

Why in the MEA1060 manual (http://www.multichannelsystems.com/sites/multichannelsystems.com/files/documents/manuals/MEA1060-Inv-BC_Manual.pdf, at pag 24) the graph of frequency response of MEA1060 PA + FA60S has a slope of only -80 dB/decade (as far as I can understand from the figure)?

Maybe some concepts are not clear for me.. Embarassed

Thank you!!!

holly87

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Re: filter slopes..

Post  Thomas on Tue Jan 29, 2013 4:15 am

Dear Holly87,

we have been carefully evaluating the slope of the filter decay at the upper limit.
The indicated slope refers only to the linear part of of the filter band decay.
140db corresponds to a decay of 7 magnitudes over 1magnitude of frequency.
I would be glad to send you a figure illustrating the calibration if you provide us with your
e-mail adress.

Thomas

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Re: filter slopes..

Post  holly87 on Tue Jan 29, 2013 8:33 pm

Dear Thomas,
thank you! my e-mail adress is: laholly@alice.it

As far as I can understand from the datasheet alone, I would expect that after 8.5 kHz (i.e., low pass cutoff of the preamplifier MEA1060), the slope of the total gain (i.e., MEA1060 PA + FA64S) is the sum of the slopes of the MEA1060 (i.e. 60 dB/dec, i.e., a decay of 3 orders of magnitude in a decade of frequency) and the FA64S (i.e., 80 dB/dec, i.e. a decay of 4 orders of magnitude), thus corresponding to a decay of 7 orders of magnitude...
Looking forward to hearing from you

Have a nice day
Holly

holly87

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Re: filter slopes..

Post  Thomas on Tue Jan 29, 2013 8:47 pm

Hi Holly,

you are perfectly right in your calculations. The only discrepancy is the fact, that we are referring just to the linear part of the decay.
The figure I show you illustrates that we observe a decay of 3,5 orders of magnitude over the interval from 10-50kHz. So the slope is equivalent to your estimated value in itīs linear part.

I mail the fihure to you via e-mail

Greetings

Thomas

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Re: filter slopes..

Post  holly87 on Tue Jan 29, 2013 10:11 pm

Dear Thomas,
thanks a lot, now it's clear!
Greetings

holly87

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