Return-Path: Received: (qmail 22312 invoked from network); 7 Apr 2000 19:10:30 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by redlabel.core.plus.net.uk with SMTP; 7 Apr 2000 19:10:30 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.02 #1) id 12de1T-0001xg-00 for rsgb_lf_group-outgoing@blacksheep.org; Fri, 07 Apr 2000 20:02:27 +0100 Received: from mail.cc.kuleuven.ac.be ([134.58.10.6]) by post.thorcom.com with esmtp (Exim 3.02 #1) id 12de1R-0001xb-00 for rsgb_lf_group@blacksheep.org; Fri, 07 Apr 2000 20:02:25 +0100 Received: from LCBD15.fys.kuleuven.ac.be (LCBD15.fys.kuleuven.ac.be [134.58.80.15]) by mail.cc.kuleuven.ac.be (8.9.3/8.9.0) with SMTP id VAA03982 for ; Fri, 7 Apr 2000 21:02:12 +0200 X-Priority: 3 X-MSMail-Priority: Normal Message-ID: <3.0.1.16.20000407205737.0957b5d8@mail.cc.kuleuven.ac.be> X-Sender: pb623250@mail.cc.kuleuven.ac.be X-Mailer: Windows Eudora Pro Version 3.0.1 (16) X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Date: Fri, 07 Apr 2000 20:57:37 To: rsgb_lf_group@blacksheep.org From: "Rik Strobbe" Subject: Re: LF: Re: LF Book, vol 2 In-reply-to: <2000040511283868199@zetnet.co.uk> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="------------090904050104060007070008" Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: This is a multi-part message in MIME format. --------------090904050104060007070008 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Hello Peter, attached you find a drawing of my antenna. As you will see I not much of an artist but I hope the picture gives you an idea how my antenna is constructed. Some explanation : N = nylon rope (120kg breaking force) S = PVC coated steel rope I = insulator X = elastic material, it's the stuff you use fix fix a basket on the back of a bike or on the roof of a car (sorry, I don't know the correct English word). L1 = base coil (variable, +/- 1.8mH) L2 = top coil (+/- 2mH) P = small wooden pole (abt. 2m) The hight of the antenna (at the ends) is 11m there is about 1m 'sack' in the middle. The antenna is supported by 4 birch trees of about 15m high and apart from the 'electrical challenge' to maximize the effeciency of the antenna there was also a 'mechanical challenge' to make the antenna survive strong winds. In the beginning I had 2 problems : - rope breaking because of strong wind - rope breaking because of 'friction' with the trees The first was solved by inserting the elastic material, in the normal state each is about 0.8m long but it can stretch to over 2m without breaking. The friction problem was solved by placing some short pieces (about 3m) of PVC coated steel rope where there is friction with the branches. The antenna is up now for 1 year without being destroyed by winds (fingers crossed). Regarding the antenna efficiency was my main problem the high loss resistance. When I started on LF (early 1998) I measured a loss of 220 Ohms ! Gradually the ground network was improved from 6 short radials (10 to 20m each) on the ground to a complex system of 6 groundrods (galvanized steel, 2.5m deep in the earth) and about 150m of galvanized iron wire interconnecting all the rods and burried about 20cm deep in the ground. But even this groundsystem the loss resistance is still 120 Ohms. Further exstensions of the ground system gave little or no reduction of the loss what make me believe that at this moment the loss is mainly in the many (several hundreds) trees surrounding the antenna rathyer than really in the ground. An unexpected result was achieved by placing a part (about 50%) of the loading coil at about 10m height. The expected gain (calculated and simulated) was only about 0.5dB but several tests and measuement showed an improvement of 4 to 5dB. A possible expanation for this unexpected gain is the fact that the voltage on the vertical part is reduced by about 50% while the topload voltage remained almost unchanged. This would mean that the unwanted 'coupling' of the antenna to the many surrounding (vertical) trees comes mainly from the vertical part of the antenna and by reducing the voltage on the vertical part also this loss is reduced. The strange thing is that I did not achieve a higher antennacurrent, the current even dropped slightly (from 1.9 to 1.85A) probably because of the extra loss in the elevated coil (since this coil had to be very light I used thin wire). With about 450WF power I get an antennacurrent of about 1.85A, estimated ERP is about 100mW. But despite this very modest ERP I managed to work over 70 stations in 17 DXCC countries over the past 2 years. This might encourage other hams to become active on LF, even when they have only limited space. 73, Rik ON7YD --------------090904050104060007070008 Content-Type: image/gif; name="ANT136.GIF" Content-Transfer-Encoding: base64 Content-Disposition: inline; filename="ANT136.GIF" R0lGODlhQQJ+AbMAAAAAAAAAqwCrAACrq6sAAKsAq6tXAKurq5eXl1dX/1f/V1f///9XV/9X ////V////ywAAAAAQQJ+AQME+/DISau9OOvNu/9gKI5kaZ5oqq5s675wLM90bd94ru987//A oHBILBqPyKRyyWw6n9CodEqtWq/YrHbL7Xq/4LB4TC6bz+i0es1uu9/wuHxOr9vv+Lx+z+/7 /4CBgoOEhYaHiImKi4yNjo+QkXUClJWWApKZmps1l56enFqflqGlU6OooKZQqZ+rr0itsqSw sbOotbk+t7y6Q7yyvsI0wMXDPcXBx8srycbMNs630NQj0s/VMNfT2d0Z287eLODc4ubk4eYm 6MDq3ezp7iHw7fLM9PH2HPj1+r78+fxdANhPICyC2AxWQFhQYSiGCR0egFhO4iaKEQ1irGgx +9LGjPo+cuzYSCRIdyZHklSUspfAlipXGoLpMiTNVjIX3ayJcifOnIh8zrInVBlQQkWH9kw6 6mghpj/PQcXlNNDUqN6uNq0KSCvVrF5dce0T9mu2sqrG7kEr9izbS2r1vG1LbS6tuHfswq2m 9y7eOX33QgtM6e8kwoUHI8ZkOM7iSooRN3b8mPGxypYns8F8r7LmNpgTD+P8eU3ozLpOl1aj 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