DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws;
  s=s1024; d=btinternet.com;
  h=Received:X-YMail-OSG:X-Yahoo-Newman-Property:Message-ID:From:To:References:Subject:Date:MIME-Version:Content-Type:Content-Transfer-Encoding:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE;
  b=4REHpDVc3PcGM2eyai/sCVKx3FCYgsMmxLxF+bLllO3BsWxtindOOOvqBttrkNVSalFy2JKzCSJ690lbJPrjxRq4LV91oyFh0JAFr3iygIqeuBZqp0Lo/ffa7c6yFZUZQWbYGHrWdCDWex+R+2PMyJEcUOjN9gpF0/X3hLFgDSw=  ;
Message-ID: <015f01c9d8ce$5f683fe0$0900a8c0@AM>
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <003001c9d8c4$719e7710$6401a8c0@asus>
Date: Tue, 19 May 2009 23:08:35 +0100
MIME-Version: 1.0
DomainKey-Status: good (testing) 
Subject: LF: Re: 518khz - Notch Filter.
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


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" <g4wgt@tiscali.co.uk>
To: "LF -RSGB LF Group" <rsgb_lf_group@blacksheep.org>
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.
>
>
>
>