Hi Sir. Oops yes its Henrys for the Inductor. My mistake. Is the other calculations correct?The units for an inductor are not μF, the are in Henrys. I get 11.255 mH (milliHenrys) using your numbers. IIRC you need the factor of 2π when doing frequency scaling since the coefficients are normalized for a radian frequency of 1 radian per second.
Hi,Hi Sir,
Thanks mind my stupidity, you are right no need for op amp.
Let me re-do this and show u what I have done.
thank you very much.
Hi Sir, im not too sure if I have to add the factor radian per second. Do you suggest I should do that?The circuit is correct. As you know frequency can be measured in Hz. (aka cycles per second) and also in radians per second. Cycles and radians are both dimensionless so the units of frequency are (1/sec). The constant of proportionality between Hz. and radians per second is 2pi. Thus:
\(\omega\;=\;2\pi f\)
I just asked if you need to include the factor of 2pi when you scale the Butterworth coefficients which are calculated for a radian frequency of 1 radian per second, when using frequencies in Hz.
Hi Sir, im not too sure if I have to add the factor radian per second. Do you suggest I should do that?The circuit is correct. As you know frequency can be measured in Hz. (aka cycles per second) and also in radians per second. Cycles and radians are both dimensionless so the units of frequency are (1/sec). The constant of proportionality between Hz. and radians per second is 2pi. Thus:
\(\omega\;=\;2\pi f\)
I just asked if you need to include the factor of 2pi when you scale the Butterworth coefficients which are calculated for a radian frequency of 1 radian per second, when using frequencies in Hz.
When you calculate the response you use radian frequency, normalized so that the corner frequencyHi Sir, im not too sure if I have to add the factor radian per second. Do you suggest I should do that?
Thank you Sir
Hi Sir, so this means my working is not correct when using 0.2251 table value?When you calculate the response you use radian frequency, normalized so that the corner frequency
\(\omega_0\;=\;1\)
and the response is
\(\frac{1}{\sqrt{2}}\)
at the corner frequency. I think I recall using that factor when scaling component values, but it was a long time ago.
Also the table value of 0.2251 appears to be incorrect. I read the table value as 1.414 or
\(\sqrt{2}\)
Ah....so
\(\frac{\large 1.414}{\large 2\pi}\;=\;0.2251\)
My simulation, using your values, is not producing good results so there may still be something wrong.
OK got it. When you simulate a passive filter with equal source and load impedances there is an insertion loss of 6 dB that must be accounted for. If you remove the filter you see the output will always be 6 dB blow the input. Now everything makes sense.
It is not true that you want to match source and load impedances in a filter. You want the impedance to be such that you get the desired characteristic; in this case maximally flat in the passband and less than or equal to some value in the transition band. Impedance matching is primarily done to transfer the maximum amount of power from the source to the load. In most filtering applications power transfer is irrelevant.Hello again,
This is interesting because i am running into a problem also, depending on how we interpret the question.
The source/load impedance is 50 ohms, so you would think that they want to match the input and output impedances with the network also. But that doesnt seem to be the case because i dont think there is any way to get 50 ohms input impedance with a 50 ohm load and still get the Butterworth response.
I get the same value for L as Papa, but when i calculate the input impedance Zin i get around 57.7 Ohms. A little mismatch, so i guess that's just too bad
I do get about -12db at 2 times the -3db frequency though.
Either you took the value from a "standard" table (1.414) and divided it by the value of 2pi to it to get 0.2251 or you used a non-standard table and pulled the value 0.2251 from it without realizing what you were doing. You would do well to do all of your filter work with the "standard" tables and radian measure, converting back to Hz. as the last step. Others will be able to follow your work without so much confusion. That's just my opinion -- you do whatever you feel comfortable doing.Hi Sir, so this means my working is not correct when using 0.2251 table value?
Thank you
Hi Sir. So this means my working is still correct?Either you took the value from a "standard" table (1.414) and divided it by the value of 2pi to it to get 0.2251 or you used a non-standard table and pulled the value 0.2251 from it without realizing what you were doing. You would do well to do all of your filter work with the "standard" tables and radian measure, converting back to Hz. as the last step. Others will be able to follow your work without so much confusion. That's just my opinion -- you do whatever you feel comfortable doing.
Here is what I consider to be the "standard" table
http://www.crbond.com/papers/btf2.pdf
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