Message-ID: <20090519232905.l4n0cl7o5vk0oogs@webmail4.kuleuven.be>
Date: Tue, 19 May 2009 23:29:05 +0200
From: Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>
To: rsgb_lf_group@blacksheep.org
References: <003001c9d8c4$719e7710$6401a8c0@asus>
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Subject: Re: LF: 518khz - Notch Filter.
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Gary,

a simple series L-C notch works best when
- Q is high =3D you need a good coil (capacitor Q shouldn't be the problem)
- the output "sees" a high impedance (FET buffer)
- the source impedance is high compared to the loss resistance of the =20
coil (eventualy put a R of a few 100 Ohm in serie with the antenna)
But it will be a hard job to get a decent attenuation at 518 while =20
passing 501-506 without too much losses.

An alternative would be a xtal filter as a passband filter for 501-506.
If you can find a number of 500kHz xtals and "polish" them up some kHz.

73, Rik  ON7YD - OR7T

Quoting Gary - G4WGT <g4wgt@tiscali.co.uk>:

> Hi LF,
>
>
>
> You may have seen an image of a NAVTEX signal on my 500KHz grabber at abou=
t
> 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 d=
ue
> 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.
>
>
>
>