Return-Path: Received: (qmail 38452 invoked from network); 8 Jan 2005 13:01:47 -0000 Received: from unknown (HELO ptb-spamcore02.plus.net) (192.168.71.3) by ptb-mailstore02.plus.net with SMTP; 8 Jan 2005 13:01:47 -0000 Received: from mailnull by ptb-spamcore02.plus.net with spamcore-l-b (Exim 4.32; FreeBSD) id 1CnGDD-000Ps9-48 for dave@picks.force9.co.uk; Sat, 08 Jan 2005 13:01:01 +0000 Received: from [192.168.67.2] (helo=ptb-mxcore02.plus.net) by ptb-spamcore02.plus.net with esmtp (Exim 4.32; FreeBSD) id 1CnGDD-000Ps6-1S for dave@picks.force9.co.uk; Sat, 08 Jan 2005 13:00:59 +0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore02.plus.net with esmtp (Exim) id 1CnGDx-0000y4-6f for dave@picks.force9.co.uk; Sat, 08 Jan 2005 13:01:45 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1CnGA1-0007Gp-2I for rs_out_1@blacksheep.org; Sat, 08 Jan 2005 12:57:41 +0000 Received: from [193.82.59.20] (helo=relay.omnieng.net) by post.thorcom.com with esmtp (Exim 4.14) id 1CnGA0-0007Gg-8a for rsgb_lf_group@blacksheep.org; Sat, 08 Jan 2005 12:57:40 +0000 Received: from mk-smarthost-9.mail.uk.tiscali.com ([212.74.114.48]) by relay.omnieng.net with esmtp (Exim 4.41) id 1CnG9v-0005A1-CQ for rsgb_lf_group@blacksheep.org; Sat, 08 Jan 2005 12:57:39 +0000 Received: from ppp-0-147.read-b-1.access.uk.tiscali.com ([80.40.88.147]:1039 helo=dshack) by mk-smarthost-9.mail.uk.tiscali.com with smtp (Exim 4.30) id 1CnG8x-0005p0-UW for rsgb_lf_group@blacksheep.org; Sat, 08 Jan 2005 12:56:36 +0000 Message-ID: <003401c4f581$8ba74cc0$93582850@dshack> From: "Dave_Richardson" To: rsgb_lf_group@blacksheep.org References: <82.1ecc794c.2f0d0993@aol.com> Date: Sat, 8 Jan 2005 12:55:46 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 Disposition-Notification-To: "Dave_Richardson" X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-SPF-Result: relay.omnieng.net: 212.74.114.48 is neither permitted nor denied by domain of tiscali.co.uk X-Spam-Score: 1.7 (+) X-Spam-Report: autolearn=no,HTML_20_30=0.474,HTML_FONT_BIG=0.1,HTML_MESSAGE=0.001,RCVD_IN_NJABL=0.1,RCVD_IN_SORBS=0.1,SARE_RECV_SPAM_DOMN81=0.853,TW_TN=0.077 Subject: LF: Re: Pre-amps on LF Content-Type: text/html; charset=windows-1252 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Status: No, hits=0.6 required=5.0 tests=HTML_20_30,HTML_FONT_BIG, HTML_MESSAGE 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 X-Spam-Filtered: by PlusNet SpamCORE (v3.00) Content-transfer-encoding: 8bit
 
----- Original Message -----
From: G0MRF@aol.com
To: rsgb_lf_group@blacksheep.org
Sent: 05 January 2005 09:12
Subject: LF: Pre-amps on LF

Adding a yxm/mrf pre-amp will overcome the loss of the input attenuator (apx 10dB) and will have a few extra dB to help things along. However, I have had a couple of mails from people who expected the pre-amps to work when they were added to simple small verticals or wires.
 
The pre-amps are 50 Ohms (ish) in and out while the  impedance of a typical 7MHz vertical is a very small fraction of 1 Ohm. The loss between them is huge. You need a matching network.
 
I remember in the early days of 136k here in the UK working one enterprising operator who had built a trasnsmitter and had matched his HF vertical by adding a reel of enamelled copper wire in series. Tuning was achieved by sliding a ferrite rod into the center of the reel and adjusting for best signal. - Wonderful!
 
A small antenna that works well is the e-field probe as promoted by AMRAD a few years ago. This is a short antenna with a very high input impedance FET amplifier.
However, the e-field probe is an exception. If you want to get any reasonable signal, you need to match the antenna................then on most amateur sets, add a pre-amp.
 
 
RE: Portable LF ATU article by G3LDO RadCom December 2003
In another posting, which I unfortunately deleted by mistake, it was suggested use of the above for matching to "short" antennas.
 
I'd be very grateful to hear from anyone who's build this ATU and got it working satisfactorily.
I can't get the LF Loading Circuit section of mine to tune-up at all, it's completely flat with any values of selected C.
I suspect it's all down to my fabrication of the Loading Coil, ferrite used etc. so it'd be very helpful if I knew at least the value of inductance I should be aiming at for this particular cct. then I can mess about with number of turns, ferrites and so on...
Mni tnx in advance.
..Dave