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Date: Fri, 17 Jan 2003 17:49:32 +0100
Message-ID: <2D280BB697C7EE4C979C5C89925418EFB05A41@TNS-FBU-2E-003.corp.telenor.no>
Thread-Topic: Notch for DCF39
Thread-Index: AcK+DlEqqfbOUde6Qhyuh4Y6ONpIbgAOLQ5w
From: jan-martin.noding@telenor.com
To: rsgb_lf_group@blacksheep.org
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Subject: LF: Re: Notch for DCF39 [G3NYK]
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Hi,

noticed something I'd wish to comment further, ref. quoted text 
from http://www.alan.melia.btinternet.co.uk/BR-t-Notch.htm

>As far as I can see at the moment the only problem is that the 
>output of the filter must not be loaded too heavily, so a FET 
>source follower is probably called for ( J310 running reasonable 
>amount of source current to keep the IMDs down ??). 

This is the wrong way to achieve high impedance (and good IMD),
it is no need to keep the "source current low" or whatever,
don't understand where one could get such assumptions from,

A simple source follower has also very low gain, probably around 0.2-0.4x 
voltage gain, but this is easily improved using an extra PNP device running
with 10-30mA, so it may even have higher gain than unity, and to improve 
the input impedance you add some positive feedback to the gate.

A more complicated solution using J310 fet was shown in Radcom some time ago,
described for my frame antenna, but I use it for my active antenna on the roof

73
Jan_Martin
LA8AK (in JO38XC)  [mailto:LA8AK@Online.no]
N4623-Kristiansand (tel.: +47-380-87178 Home)(38052660 Work 90777126 Mobile)
http://www.laud.no/la6nca/LA8AK/ 

----- Original Message ----- 
From: Alan Melia [mailto:Alan.Melia@btinternet.com]
Send: 17. januar 2003 10:45


Hi all, a belated Chrismas present to the Group. As a result of a discussion
with Hugh M0WYE,  I calculated, and simulated a Bridged-T Notch Filter for
136kHz, which should reduce the level of DCF39 by about 30dB which only
giving about 2 or 3 dB loss at the top of the band. Hugh has made up the
filter and from workbench tests it seems promising. It occurs to me that
this may be of interest to those living closer to Burg that we do.

Details on http://www.alan.melia.btinternet.co.uk/BR-t-Notch.htm

We would be interested if anyone finds it useful.

Cheers de Alan G3NYK
alan.melia@btinternet.com
http://www.alan.melia.btinternet.co.uk