EMRFD Message Archive 2744
Message Date From Subject 2744 2009-02-26 17:57:57 David Siegrist nescaf notch filter Hey Sam,
I have attached a page of notes on the filter. I would think that it might be a good starting point to create a notch filter. The design lends itself well to the change. I imagine you will need to change the value of r2/r5, and take the output from 3/18. The NEscaf is mode 1 from the mf100 ap notes. The schematic is posted on the NEQrp website, and all are welcome to extend it, as I did to get here.
If you do end up doing it, please let the NEQrp know, and we will post it on the website.
I will offer my thanks again to Sam Ulbing, N4UAU who published the initial design in QST.
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2745 2009-02-26 19:19:15 Graham / KE9H Re: nescaf notch filter David:
Yahoo does not allow attachments and always removes them.
2747 2009-02-27 07:22:21 dave Re: nescaf notch filter the document was also uploaded into the files directory.
2748 2009-02-27 07:54:07 Chris Trask Re: nescaf notch filter >I've downloaded the notes from the files section. Could someone email me the PDF file for the 1992 QST article that this refers to? I've also used those National Semiconductor switched-capacitor filter ICs and I'm curious to see what the implementation is here.
> I have attached a page of notes on the filter. I would think
> that it might be a good starting point to create a notch filter.
> The design lends itself well to the change.
Interesting that this should come up as I'm presently working on a noise blanker to rid me of some annoying EMI from numerous defectiove sodium vapour lights and other noise sources. I'm almost finished with a solid-state implementation of the Collins noise blanker that was in some of their tube receivers.
Once I'm rid of the bulk of the noise at the receiver input, I anticipate that there will be some residual noise that will need to be dealt with, and this thread has reminded me of an earlier realization of switched capacitor filters known as N-path. In essence, they are actually a sychronous comb filter. Changing the frequency is simply a matter of changing the clock rate as with the National Semiconductor ICs, and the bandwidth is adjusted with a single potentiometer.
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