Hi Gary see the "notch" I designed for Hugh to reduce DCF39 a little at
http://www.alan.melia.btinternet.co.uk/BR-t-Notch.htm
The plot will give some idea of the possible reduction in wanted signal. The
trick is you want the highest "Q" you can get this involved usually using a
small inductor and a large cap. The other problem is that they dont like a
low impedance load on the output so you need to put an emitter (or source)
follower before the RX input. I can only suggest try it and see. I think it
should work reasonably well, DCF39 is a lot closer to 136 than 518 is to 502
relatively speaking. A top-coupled band-pass filter would also work quite
well but I am not sure whether you would get enough rejection on the high
side.
The LC is resonant at the notch frequency and the pot is connected to the
centre-tap.
The plot is from the (free) analyser program on my site too. There may even
be a node-list for it in the download examples.
Alan G3NYK
----- Original Message -----
From: "Gary - G4WGT" <[email protected]>
To: "LF -RSGB LF Group" <[email protected]>
Sent: Tuesday, May 19, 2009 9:57 PM
Subject: LF: 518khz - Notch Filter.
> Hi LF,
>
>
>
> You may have seen an image of a NAVTEX signal on my 500KHz grabber at
about
> 506KHz. The original of this image is at 518KHz. The receiver for this
> grabber is a Softrock Lite 455KHz module modified for 500KHz.
>
>
>
> I have attempted to notch the signal using a simple series or parallel
> filter but only succeeded in seriously degrading the whole band possibly
due
> to the bandwidth of the filter??
>
>
>
> Is there some simple narrow notch filter which I could use to remove the
> offending signal.
>
>
>
> 73,
>
>
>
> Gary - G4WGT - IO83QP.
>
>
>
>
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