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Author Topic: Wanted: Info on making higher Q notch filters  (Read 1575 times)
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WA2SQQ
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« on: December 14, 2020, 01:58:13 PM »

I’m doing some experimenting trying to build very sharp notch filters for the a.m. broadcast band. I’ve discovered that using larger value silver mica capacitors seems to improve the Q. I’m wondering if anyone has any data that shows the advantages or disadvantages using different gauges of wire? The first coil that I built I used some 24 gauge Kynar wire left over from the wire wrap days. I used a piece of PVC pipe as the coil form. I’m wondering if winding the coil on a ferrite rod might increase the Q. any suggestions would be appreciated
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WBear2GCR
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Brrrr- it's cold in the shack! Fire up the BIG RIG


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« Reply #1 on: December 14, 2020, 02:19:55 PM »

Afaik, the wire makes no difference in the BC band.
Series DCR and reactance matters, as does the inherent quality of the cap
at the frequencies of interest. So, iirc ESR matters.

I think the Q factor for coils may be improved with the use of ferrite
cores... assuming proper selection. I'm weak in that area.

But if you are trying to notch out one particular station, then multi-pole filters
would be the way to go. Possibly a crystal filter might fly?
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Patrick J. / KD5OEI
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« Reply #2 on: December 15, 2020, 02:45:09 AM »

At BC frequencies, could a gyrator act as the inductance with high Q?

chapter 6
https://www.ti.com/lit/an/sboa093a/sboa093a.pdf

http://tools.griffineffects.com/gyrator.php

just a late night thought.
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