Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dc03.r1000.mx.aol.com (Internet Inbound) with ESMTP id 49A863800009B; Fri, 26 Apr 2013 19:46:27 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1UVsKI-000465-HQ for rs_out_1@blacksheep.org; Sat, 27 Apr 2013 00:45:14 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1UVsKH-00045w-SY for rsgb_lf_group@blacksheep.org; Sat, 27 Apr 2013 00:45:13 +0100 Received: from omr-d08.mx.aol.com ([205.188.109.207]) by relay1.thorcom.net with esmtp (Exim 4.77) (envelope-from ) id 1UVsKE-00071w-OF for rsgb_lf_group@blacksheep.org; Sat, 27 Apr 2013 00:45:12 +0100 Received: from mtaout-mb06.r1000.mx.aol.com (mtaout-mb06.r1000.mx.aol.com [172.29.41.70]) by omr-d08.mx.aol.com (Outbound Mail Relay) with ESMTP id 91E167001F852 for ; Fri, 26 Apr 2013 19:42:23 -0400 (EDT) Received: from Black (188-195-246-26-dynip.superkabel.de [188.195.246.26]) by mtaout-mb06.r1000.mx.aol.com (MUA/Third Party Client Interface) with ESMTPA id B6DB5E000097 for ; Fri, 26 Apr 2013 19:42:22 -0400 (EDT) Message-ID: <3D784CBB778342CABB2AB4CCDC45ACC5@Black> From: "Markus Vester" To: References: ,<517ABCE1.8060802@iup.uni-heidelberg.de>, In-Reply-To: Date: Sat, 27 Apr 2013 01:41:49 +0200 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Windows Mail 6.0.6002.18197 X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6002.18463 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20121107; t=1367019743; bh=qU4bqz+KCMrOKjSmtUs6FSnlEJ341FQcmPNF/auM3mI=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=VcZmwfJfbdr+nyA8yQ5rPZXkMKprfnyrEUB0kTYP6PO3T3Eh5rGRWgye7KKtbWKB4 BuZnJ0j1kUDMRxoLDD7YZVUyxhtF+GZglufnd2LDxDHEb9rDqZUu6eaw+iKXSG8LAF tRN+yVTYjE1eXRol4LTt14kVZutMQgXq12yECFk4= X-AOL-SCOLL-SCORE: 0:2:462951264:93952408 X-AOL-SCOLL-URL_COUNT: 0 X-Spam-Score: 0.0 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has identified this incoming email as possible spam. The original message has been attached to this so you can view it (if it isn't spam) or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: Warren, Laurence, the earth losses beneath the loop could either be inductive or capacitive. In reality probably both, but which effect dominates depends on voltages, surroundings (branches etc), and also ground conductivity (higher conductivity increases eddy currents but lowers capacitive losses). Ideally you would have maximum voltage at the capacitor terminals and zero in the middle of the loop. One way to generally reduce voltages for a given inductance would be to split the resonance C into several larger pF capacitors in series, distributed around the circumference. This is often done with MRI loop antennas ("surface coils") to minimize resistive coupling to the patient's skin. [...] Content analysis details: (0.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (markusvester[at]aol.com) -0.0 SPF_PASS SPF: sender matches SPF record -0.0 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain 0.0 HTML_MESSAGE BODY: HTML included in message 0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid X-Scan-Signature: 16ae5a6b0cd8af8ba18c7df6d1df8b5a Subject: LF: Re: Was Fire in the wire Content-Type: multipart/alternative; boundary="----=_NextPart_000_0014_01CE42E8.62D1B700" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.9 required=5.0 tests=HTML_30_40,HTML_MESSAGE, MISSING_OUTLOOK_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 x-aol-global-disposition: G X-AOL-SCOLL-AUTHENTICATION: mtain-dc03.r1000.mx.aol.com ; domain : mx.aol.com DKIM : fail X-AOL-OVERRIDE-PIK-REASON: Y x-aol-sid: 3039ac1d4083517b11d202d9 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none This is a multi-part message in MIME format. ------=_NextPart_000_0014_01CE42E8.62D1B700 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Warren, Laurence, the earth losses beneath the loop could either be inductive or = capacitive. In reality probably both, but which effect dominates depends = on voltages, surroundings (branches etc), and also ground conductivity = (higher conductivity increases eddy currents but lowers capacitive = losses). Ideally you would have maximum voltage at the capacitor = terminals and zero in the middle of the loop. One way to generally = reduce voltages for a given inductance would be to split the resonance C = into several larger pF capacitors in series, distributed around the = circumference. This is often done with MRI loop antennas ("surface = coils") to minimize resistive coupling to the patient's skin. Best 73, Markus ----- Original Message -----=20 From: Laurence KL1 X=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Saturday, April 27, 2013 1:09 AM Subject: LF: Was Fire in the wire Thanks Warren - interesting stuff ! =20 Certainly the ground beneath the loop is probably a couple of Kv pd = above the conductor at my Kw level - I can create colorful violet = coronas :-) - and the capacitive affects of raising the or lowering the = horizontal section of the loop just a few feet make a lot of change to = the tuning -=20 =20 Ive followed a suggestion to "relieve" earth losses/add a little more = tuning stability by shoving a Earth mat under the loop here - at the = moment it is untuned but installing it did cause an increase in loop = current by a couple of percent - I saw a paper tuning this earth and it = is was said to improve the stability and increase the effective power in = this NVIS set up at 137. =20 Im using the underslung pulley system on mine at the moment which has = survived one Alaskan winter :-) Rough diagram attached - there are two = parallel conductors in this loop but a single black line is shown for = clarity - adding a second conductor didnt change the efficiency much on = 505kHz where its nearly resonant, but helped on 137 =20 http://kl7uk.com/loopy.jpg =20 Cheers Laurence KL 1X WE2 XPQ Alaska =20 -------------------------------------------------------------------------= ------- Date: Fri, 26 Apr 2013 17:47:51 -0400 From: wd2xgj@gmail.com To: rsgb_lf_group@blacksheep.org Subject: Re: LF: Fire in the wire Hi Stefan, There are thousands or perhaps tens of thousands of volts from = the loop to ground. If I grounded the loop with and there was a large potential difference, = wouldn't that cause a large current to flow to ground and effectively = shunt my signal to ground? 73 Warren On Fri, Apr 26, 2013 at 1:44 PM, Stefan Sch=E4fer = wrote: Warren, What is the voltage between the tree (GND) and loop? I thought that = the voltages are rather small, i.e. below 100V, especially when a large = loop is used. Isn't it possible to ground the loop? 73, Stefan Am 26.04.2013 19:21, schrieb Warren Ziegler: Just a quick report on a failure mode for LF TX antennas. Last Fall my original TX loop made up of approximately 500 feet of = RG-11 coax suspended from trees went open circuit (both center conductor = and shield), some time later part of the wire actually came down. I had = thought that abrasion from contact with the trees had eventually worn = through it. What I found was a little more interesting. Looking at the downed = end, it appeared that the insulation had melted for a considerable = distance and there were burn marks further up the cable. My hypothesis = is that the outer insulation was abraded away and the coax shield came = into contact with the tree limb causing the burning/melting. Will try to get some pictures this weekend and put them up on my = website. Long term if one wants to operate at the kW level either better = insulation or a better way of supporting the antenna than trees would be = required! --=20 73 Warren K2ORS WD2XGJ WD2XSH/23 WE2XEB/2 WE2XGR/1 --=20 73 Warren K2ORS WD2XGJ=20 WD2XSH/23 WE2XEB/2 WE2XGR/1 ------=_NextPart_000_0014_01CE42E8.62D1B700 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Warren, Laurence,
 
the earth losses beneath the loop could = either be=20 inductive or capacitive. In reality probably both, but which effect = dominates depends on voltages, surroundings (branches etc), and also = ground=20 conductivity (higher conductivity increases eddy currents but = lowers=20 capacitive losses). Ideally you would have maximum voltage at the = capacitor=20 terminals and zero in the middle of the loop. One way to generally = reduce=20 voltages for a given inductance would be to split the resonance C into = several=20 larger pF capacitors in series, distributed around the circumference.=20 This is often done with MRI loop antennas ("surface coils") to = minimize resistive coupling to the patient's skin.
 
Best 73,
Markus
 
----- Original Message -----=20
From: Laurence KL1 X
Sent: Saturday, April 27, 2013 1:09 AM
Subject: LF: Was Fire in the wire

Thanks Warren - interesting stuff = !
 
Certainly the=20 ground beneath the loop is probably a couple of Kv pd above the = conductor at my=20 Kw level - I can create colorful violet coronas :-) - and the=20 capacitive affects of raising the or lowering the horizontal section of = the loop=20 just a few feet make a lot of change to the tuning - =
 
Ive=20 followed a suggestion to "relieve" earth losses/add a little more tuning = stability by shoving a Earth mat under the loop here - at = the=20 moment it is untuned but installing it did cause an increase = in loop=20 current by a couple of percent - I saw a paper tuning this = earth and=20 it is was said to improve the stability and increase the effective = power in=20 this NVIS set up at 137.
 
Im using the underslung pulley = system on=20 mine at the moment which has survived one Alaskan winter :-)  = Rough=20 diagram attached - there are two parallel conductors in this loop but a = single=20 black line is shown for clarity - adding a second conductor didnt change = the=20 efficiency much on 505kHz where its nearly resonant, but helped  on = 137
 
http://kl7uk.com/loopy.jpg
&nb= sp;
Cheers
Laurence=20 KL 1X  WE2 XPQ
Alaska

 
Date: Fri, 26 Apr 2013 17:47:51 -0400
From: wd2xgj@gmail.com
To:=20 rsgb_lf_group@blacksheep.org
Subject: Re: LF: Fire in the = wire

Hi Stefan,

       There are thousands or perhaps tens of = thousands=20 of volts from the loop to ground.
If I grounded the loop with and there was a large potential = difference,=20 wouldn't that cause a large current to flow to ground and effectively = shunt my=20 signal to ground?

73 Warren



On Fri, Apr 26, 2013 at 1:44 PM, Stefan = Sch=E4fer <Stefan.Schaefer@iup.uni-heidelberg.de> = wrote:
Warren,

What is the voltage between the = tree (GND)=20 and loop? I thought that the voltages are rather small, i.e. below = 100V,=20 especially when a large loop is used. Isn't it possible to ground the=20 loop?

73, Stefan

Am 26.04.2013 = 19:21,=20 schrieb Warren Ziegler:


Just a quick report on a failure mode for LF = TX=20 antennas.
Last Fall my original TX loop made up of approximately = 500 feet=20 of RG-11 coax suspended from trees went open circuit (both center = conductor=20 and shield), some time later part of the wire actually came down. I = had=20 thought that abrasion from contact with the trees had eventually = worn=20 through it.

What I found was a little more interesting. = Looking at=20 the downed end, it appeared that the insulation had melted for a=20 considerable distance and there were burn marks further up the = cable. My=20 hypothesis is that the outer insulation was abraded away and the = coax shield=20 came into contact with the tree limb causing the = burning/melting.
Will=20 try to get some pictures this weekend and put them up on my=20 website.

Long term if one wants to operate at the kW level = either=20 better insulation or a better way of supporting the antenna than = trees would=20 be required!

--
73 Warren K2ORS
      =  =20         WD2XGJ
        =  =20       WD2XSH/23
          =  =20     WE2XEB/2
            =  =20   = WE2XGR/1




-- =
73 Warren=20 K2ORS
                WD2XGJ=20
                = WD2XSH/23
 =20               WE2XEB/2
  =  =20             WE2XGR/1

 =20
------=_NextPart_000_0014_01CE42E8.62D1B700--