X-GM-THRID: 1234354605813391461 X-Gmail-Labels: rsgb lf Delivered-To: daveyxm@gmail.com Received: by 10.35.22.8 with SMTP id z8cs181159pyi; Sat, 21 Apr 2007 09:18:05 -0700 (PDT) Received: by 10.66.221.6 with SMTP id t6mr3706090ugg.1177172284758; Sat, 21 Apr 2007 09:18:04 -0700 (PDT) Return-Path: Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mx.google.com with ESMTP id 54si1156598ugp.2007.04.21.09.18.02; Sat, 21 Apr 2007 09:18:04 -0700 (PDT) Received-SPF: neutral (google.com: 193.82.116.20 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1HfIAN-0001nX-8B for rs_out_1@blacksheep.org; Sat, 21 Apr 2007 17:10:27 +0100 Received: from [193.82.59.130] (helo=relay2.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1HfIAM-0001nO-G5 for rsgb_lf_group@blacksheep.org; Sat, 21 Apr 2007 17:10:26 +0100 Received: from imo-m20.mx.aol.com ([64.12.137.1]) by relay2.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1HfIAL-00038V-90 for rsgb_lf_group@blacksheep.org; Sat, 21 Apr 2007 17:10:26 +0100 Received: from G0MRF@aol.com by imo-m20.mx.aol.com (mail_out_v38_r9.1.) id l.c76.efa8d1e (41811) for ; Sat, 21 Apr 2007 12:10:14 -0400 (EDT) From: G0MRF@aol.com Message-ID: Date: Sat, 21 Apr 2007 12:10:14 EDT To: rsgb_lf_group@blacksheep.org MIME-Version: 1.0 X-Mailer: 9.0 SE for Windows sub 5014 X-Spam-Flag: NO X-Spam-Score: -0.1 (/) X-Spam-Report: autolearn=disabled,AWL=-0.607,HTML_MESSAGE=0.001,NO_REAL_NAME=0.55 Subject: LF: 500 - Preamp conversion. Content-Type: multipart/alternative; boundary="-----------------------------1177171814" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: * X-Spam-Status: No, hits=1.1 required=5.0 tests=HTML_30_40,HTML_MESSAGE, NO_REAL_NAME autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false Status: O X-Status: X-Keywords: X-UID: 2114 -------------------------------1177171814 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Hi all. If anyone is having sensitivity issues with their receiver, then it is possible to convert the G3YXM / G0MRF pre-amp from 136kHz to 503kHz. This is not an 'ideal' solution as the inductors used for 136k are quite large. However, a little testing earlier today has shown this works. Circuit: _www.g0mrf.freeserve.co.uk/preamp.htm_ (http://www.g0mrf.freeserve.co.uk/preamp.htm) You will need 2 x 470pF and 1 x 47pF Remove C1 to C7 keeping the 2 x 4n7 Replace / add the capacitors as follows: C1 + C7 4n7 - As removed from the 136kHz pre-amp C3 C6 Not needed C2 + C5 470pF C4 47pF The pre-amp can be peaked to give 11dB gain at 502 kHz with a bandwidth of about 25kHz. The response is slightly over coupled in that it has signs of a double hump response but the overall performance is quite good. it certainly cuts out all the intermod from the big medium wave transmission on 558kHz that caused problems here and compensates for the attenuators in the radio. 73 David G0MRF -------------------------------1177171814 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Hi all.
 
If anyone is having sensitivity issues with their receiver, then it is=20 possible to convert the G3YXM / G0MRF pre-amp from 136kHz to 503kHz.
 
This is not an 'ideal' solution as the inductors used for 136k=20 are quite large.  However, a little testing earlier today has show= n=20 this works.
 
Circuit: www.g0mrf.freeserve.co.= uk/preamp.htm
 
You will need   2 x 470pF and 1 x 47pF
 
Remove C1 to C7     keeping the 2 x 4n7
 
Replace / add the capacitors as follows:
 
C1 + C7       4n7    - As=20 removed from the 136kHz pre-amp
C3 C6          Not=20 needed
C2 + C5      470pF
C4           &nb= sp; =20 47pF
 
The pre-amp can be peaked to give 11dB gain at 502 kHz with a bandwidth= of=20 about 25kHz.
The response is slightly over coupled in that it has signs of a double=20= hump=20 response but the overall performance is quite good. it certainly cuts out al= l=20 the intermod from the big medium wave transmission on 558kHz that caused=20 problems here and compensates for  the attenuators in the radio.
 
73
 
David  G0MRF
 
         
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