Re: LF: 518khz - Notch Filter.

[Andy Talbot <andy.g4jnt@googlemail.com>]

Answers to all comments.

 

It was modelled with lossless components.  I didn't have to time to do any mofre than a basic cesign..   But its a relativlely benign filter so inductors with Qu of 40 pluss should be OK.

 

Ansoft Designer is downloadable from Ansoft  http://www.ansoft.com/ansoftdesignersv/  You need to register, but teh student version is free.   

 

Its BIG !

 

 

Andy  G4JNT
wobbleU cubed .g4jnt.kom

2009/5/20 Ken <ken.h.wright@btinternet.com>

Hi Andy.

Where can I obtain a copy of Ansoft Designer from, I usually use Addie for filters, a second option would be worth having.

 

73

Ken

 

M0KHW 

----- Original Message -----

From: Andy Talbot

To: rsgb_lf_group@blacksheep.org

Sent: Tuesday, May 19, 2009 11:07 PM

Subject: Re: LF: 518khz - Notch Filter.

Ansoft Designer came up with this solution. 

 

http://www.g4jnt.com/518kHz_BandStop.gif

 

The component values aren't particulalrly nice, and there is almost certainly a nicer design with transformers to be found, but...

Andy  G4JNT

2009/5/19 Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>

Gary,

a simple series L-C notch works best when
- Q is high = 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 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 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 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.