Return-Path: Received: from rly-dd08.mx.aol.com (rly-dd08.mail.aol.com [172.19.141.155]) by air-dd02.mail.aol.com (v121.4) with ESMTP id MAILINDD024-b93483ec9cf1e6; Thu, 29 May 2008 11:21:16 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-dd08.mx.aol.com (v121.5) with ESMTP id MAILRELAYINDD085-b93483ec9cf1e6; Thu, 29 May 2008 11:20:49 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1K1jvJ-0005lb-VL for rs_out_1@blacksheep.org; Thu, 29 May 2008 16:20:13 +0100 Received: from [193.82.59.130] (helo=relay2.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1K1jvJ-0005lS-43 for rsgb_lf_group@blacksheep.org; Thu, 29 May 2008 16:20:13 +0100 Received: from imo-m23.mx.aol.com ([64.12.137.4]) by relay2.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1K1jvE-00011l-P2 for rsgb_lf_group@blacksheep.org; Thu, 29 May 2008 16:20:12 +0100 Received: from MarkusVester@aol.com by imo-m23.mx.aol.com (mail_out_v38_r9.4.) id l.d2e.220a3d2b (34905) for ; Thu, 29 May 2008 11:19:56 -0400 (EDT) Received: from webmail-stg-d09 (webmail-stg-d09.sim.aol.com [205.188.162.30]) by cia-da02.mx.aol.com (v121.5) with ESMTP id MAILCIADA022-8859483ec99b15; Thu, 29 May 2008 11:19:55 -0400 References: <89975.60723.qm@web27612.mail.ukl.yahoo.com> <20080522083548.021D331E703@smtps01.kuleuven.be> <1JzI3q-1TRrQ80@fwd33.t-online.de> <4836C5DA.1090806@mbsks.franken.de> <20080529073300.EBDE831E703@smtps01.kuleuven.be> To: rsgb_lf_group@blacksheep.org Date: Thu, 29 May 2008 11:19:55 -0400 In-Reply-To: <20080529073300.EBDE831E703@smtps01.kuleuven.be> X-MB-Message-Source: WebUI MIME-Version: 1.0 From: Markus Vester X-MB-Message-Type: User X-Mailer: AOL Webmail 36743-STANDARD Received: from 217.194.34.103 by webmail-stg-d09.sysops.aol.com (205.188.162.30) with HTTP (WebMailUI); Thu, 29 May 2008 11:19:55 -0400 Message-Id: <8CA8FB6956F1036-C94-810@webmail-stg-d09.sysops.aol.com> X-Spam-Flag:NO X-Spam-Score: -0.1 (/) X-Spam-Report: autolearn=disabled,AWL=-0.433,FORGED_AOL_TAGS=0.281,HTML_MESSAGE=0.001,UNPARSEABLE_RELAY=0.001 Subject: Re: LF: antenna losses Content-Type: multipart/alternative; boundary="--------MB_8CA8FB695A84846_C94_FDD_webmail-stg-d09.sysops.aol.com" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=FORGED_AOL_TAGS,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-AOL-IP: 193.82.116.20 X-AOL-SCOLL-AUTHENTICATION: listenair ; SPF_helo : n X-AOL-SCOLL-AUTHENTICATION: listenair ; SPF_822_from : + ----------MB_8CA8FB695A84846_C94_FDD_webmail-stg-d09.sysops.aol.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Hi Rik, playing with your figures for current and resistance, one=C2=A0finds that th= e=C2=A0poor little twig=C2=A0would have dissipated 91 watts. Makes me=C2=A0w= orry whether=C2=A0it could=C2=A0have started a bushfire... During a fieldday= a couple of years ago, we ignited bits of dry grass on the LF antenna wire=20= for demonstration, which=C2=A0did create=C2=A0some respect for RF voltage am= ongst the bystanders. 73 and best of luck Markus, DF6NM -----Urspr=C3=BCngliche Mitteilung-----=20 Von: Rik Strobbe An: rsgb_lf_group@blacksheep.org Verschickt: Do., 29. Mai. 2008, 9:37 Thema: LF: antenna losses Dear all,=C2=A0 =C2=A0 as I tried to tune my 500 kHz antenna last right I noticed that it was detun= ed by about 1.5 kHz (from 503 tot 501.5) and that the antenna current was do= wn to 1.8 A (from 2.1 A).=C2=A0 A first visual control of the antenna revealed no possible cause. So I start= ed to check the coax cables and variometer, but all was OK there.=C2=A0 During a second visual control (it was already getting dark) I noticed that=20= a small branch of one of the surrounding trees was cracked (probably during=20= a thunderstorm the night before) and just one leaf was touching the antenna=20= wire. By gently pulling the downlead wire of the antenna a few times the cra= cked branch moved a bit and the leaves were now about 20 cm from the antenna= wire. Now the antenna was back to 503 kHz and the antenna current back to 2= .1 A.=C2=A0 =C2=A0 Of course I know that the antenna wire should not touch any greenery, but I=20= was surprised of the rather large effect of just one (meanwhile dry) leave t= ouching the antenna wire (that has 1mm plastic isolation).=C2=A0 =C2=A0 The loss resistance of my antenna system now is 78 Ohm, including 10 Ohm coi= l losses (with no touching leaves).=C2=A0 Few weeks ago I increased the height of the top wire from 9 m to 11 m, what=20= slightly increase the loss from 73 to 78 Ohm.=C2=A0 This is would bring the signal about 0.3 dB down, but is more than compensat= ed by the increase of the radiation resistance (+1.7 dB)=C2=A0 =C2=A0 During the first tests in February (with the 9m high antenna) I measured a l= oss of 55 Ohm, so the is a seasonal variation almost 20 Ohm (or 1.2 dB).=C2= =A0 =C2=A0 73, Rik ON7YD - OR7T=C2=A0 =C2=A0 Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm=C2=A0 =C2=A0 ________________________________________________________________________ Bei AOL gibt's jetzt kostenlos eMail f=C3=BCr alle. Klicken Sie auf AOL.de=20= um heraus zu finden, was es sonst noch kostenlos bei AOL gibt. ----------MB_8CA8FB695A84846_C94_FDD_webmail-stg-d09.sysops.aol.com Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="utf-8" Hi Rik,

playing with your figures for current and resistance, one finds that th= e poor little twig would have dissipated 91 watts. Makes me w= orry whether it could have started a bushfire... During a fieldday= a couple of years ago, we ignited bits of dry grass on the LF antenna wire=20= for demonstration, which did create some respect for RF voltage am= ongst the bystanders.

73 and best of luck
Markus, DF6NM


-----Urspr=C3=BCngliche Mitteilung-----
Von: Rik Strobbe <rik.strobbe@fys.kuleuven.be>
An: rsgb_lf_group@blacksheep.org
Verschickt: Do., 29. Mai. 2008, 9:37
Thema: LF: antenna losses

Dear all, 
 
as I tried to tune my 500 kHz antenna last right I noticed that it was detun= ed by about 1.5 kHz (from 503 tot 501.5) and that the antenna current was do= wn to 1.8 A (from 2.1 A). 
A first visual control of the antenna revealed no possible cause. So I start= ed to check the coax cables and variometer, but all was OK there. 
During a second visual control (it was already getting dark) I noticed that=20= a small branch of one of the surrounding trees was cracked (probably during=20= a thunderstorm the night before) and just one leaf was touching the antenna=20= wire. By gently pulling the downlead wire of the antenna a few times the cra= cked branch moved a bit and the leaves were now about 20 cm from the antenna= wire. Now the antenna was back to 503 kHz and the antenna current back to 2= .1 A. 
 
Of course I know that the antenna wire should not touch any greenery, but I=20= was surprised of the rather large effect of just one (meanwhile dry) leave t= ouching the antenna wire (that has 1mm plastic isolation). 
 
The loss resistance of my antenna system now is 78 Ohm, including 10 Ohm coi= l losses (with no touching leaves). 
Few weeks ago I increased the height of the top wire from 9 m to 11 m, what=20= slightly increase the loss from 73 to 78 Ohm. 
This is would bring the signal about 0.3 dB down, but is more than compensat= ed by the increase of the radiation resistance (+1.7 dB) 
 
During the first tests in February (with the 9m high antenna) I measured a l= oss of 55 Ohm, so the is a seasonal variation almost 20 Ohm (or 1.2 dB).&nbs= p;
 
73, Rik ON7YD - OR7T 
 
Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm 
 
Bei AOL gibt's jetzt kostenlos eMail für alle! Was es sonst noch umsons= t bei AOL gibt, finden Sie hier heraus AOL.de.
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