Inductor for low frquency filter
Inductor for low frquency filter
(OP)
I am trying to build a 5KHz passive elliptic LPF for harmonic supression. The problem was that the 1.2mH axial high current inductor caused a severe harmonic distortion. The frequecy response was exactly as it supposed to be designed. But the filter introduced higher harmonics rather than to suppress them.
Do you guys know a better inductor capable for this filter?
Do you guys know a better inductor capable for this filter?





RE: Inductor for low frquency filter
<nbucska@pcperipherals.com>
RE: Inductor for low frquency filter
But the problem was through the passive filter the harmonics were "amplified" to just -60dBc. I am pretty sure that the inductor caused the distortion.
I want to find a 1.2mH inductor for this filter not to induce the harmonic distortion. I hope you guys have some experience with this problem.
RE: Inductor for low frquency filter
from ext. magnetic field, too. What is your waveform or
spectrum and amplitude ?
<nbucska@pcperipherals.com>
RE: Inductor for low frquency filter
Active device normally be more distortable than passive device. That's why I went to use passive filters.
RE: Inductor for low frquency filter
Just a thought (I don't know too much about inductor technology).
RE: Inductor for low frquency filter
But the problem was through the passive filter the harmonics were "amplified" to just -60dBc. I am pretty sure that the inductor caused the distortion.
I want to find a 1.2mH inductor for this filter not to induce the harmonic distortion. I hope you guys have some experience with this problem.
RE: Inductor for low frquency filter
RE: Inductor for low frquency filter
RE: Inductor for low frquency filter
output circuit may pick up the noise or radiation
generated by your input circuit. You may need shielding
or more careful layout.
<nbucska@pcperipherals.com>
RE: Inductor for low frquency filter
RE: Inductor for low frquency filter
From my experience designing modem filters I think you may find that even at 5kHz you will require very careful layout - and measurement technique - to achieve a real 110dB attentuation. Have you actually measured the noise spectrum from the filter, because it is very easy to pick up noise at those sort of expected low levels from other test equipment, e.g. PC c.r.t. screens, which can add to the apparent output voltage from the filter.
RE: Inductor for low frquency filter
RE: Inductor for low frquency filter
task to get -110 dB.
I measured at 1 MHz. -60dB between two 1/4 W resistors
at 6".
You can try to divide the 1.2 mH into two and arrange them
antiparallel, or rotate it to minimum. Try shielding, better grounding scheme, etc.
<nbucska@pcperipherals.com>
RE: Inductor for low frquency filter
I am going to try the inductor built with either air core or iron core, which are used for audio frequency.
RE: Inductor for low frquency filter
would help us to know, what you are trying to do and why ?
My experience is that if something is very difficult, often
it is an indication that we picked a very long shortcut.
<nbucska@pcperipherals.com>
RE: Inductor for low frquency filter
- they sell direct.. Note I have no affiliation with them in any way.
RE: Inductor for low frquency filter
I appreciate your help very much.
RE: Inductor for low frquency filter
Interesting, I have had lots of problems with ceramic caps and distortion in audio circuits.. Note Y5V dielectric is about the worst and X7R isn't much better, anything above 0.1uF should be regarded with suspicion in a ceramic. Unfortunately ceramics are quite microphonic too, and this correlates well to the distortion problem as well. Tantalums are better in terms of distortion and generally non microphonic, still not my first choice. Polypropylene are quite good, however just like large ceramics they can be microphonic, so if this is a problem there are special relatively non-microphonic types available.. (Tighter wrap I believe.)