Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-ma03.r1000.mx.aol.com (Internet Inbound) with ESMTP id DE803380000AB; Tue, 24 Jul 2012 14:40:30 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Stk19-0002uX-Uq for rs_out_1@blacksheep.org; Tue, 24 Jul 2012 19:39:35 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Stk19-0002uO-0t for rsgb_lf_group@blacksheep.org; Tue, 24 Jul 2012 19:39:35 +0100 Received: from nm20-vm0.bullet.mail.ukl.yahoo.com ([217.146.183.115]) by relay1.thorcom.net with smtp (Exim 4.77) (envelope-from ) id 1Stk16-0000sk-Ud for rsgb_lf_group@blacksheep.org; Tue, 24 Jul 2012 19:39:33 +0100 Received: from [217.146.183.208] by nm20.bullet.mail.ukl.yahoo.com with NNFMP; 24 Jul 2012 18:39:31 -0000 Received: from [217.146.183.203] by tm1.bullet.mail.ukl.yahoo.com with NNFMP; 24 Jul 2012 18:39:31 -0000 Received: from [127.0.0.1] by omp1001.bt.mail.ukl.yahoo.com with NNFMP; 24 Jul 2012 18:39:31 -0000 X-Yahoo-Newman-Id: 614375.88476.bm@omp1001.bt.mail.ukl.yahoo.com Received: (qmail 42649 invoked from network); 24 Jul 2012 18:39:31 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s1024; t=1343155171; bh=JtWpoNa3S39uTQ02k8Q+gPwQxf1m8wXG88h4LnWtxHw=; h=X-Yahoo-Newman-Property:X-YMail-OSG:X-Yahoo-SMTP:Received:Message-ID:From:To:References:In-Reply-To:Subject:Date:MIME-Version:Content-Type:Content-Transfer-Encoding:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE; b=D9bVheWnU5IAGCFXg654qHvfVbV0jbQywMxf5fGcLG7gG7gwB4W/ESacF7M0/QPJ0zPYQdmf63HHS8v/exUAM8e2ffnhZ/PpeTidAjL1ZnjQc6PnYUf3o+9HAamNMJd9L8ZtRBDJBrR9H6sfbGxaC80wiW/yerQGE6JEWy7k4rg= X-Yahoo-Newman-Property: ymail-3 X-YMail-OSG: .HBvXwoVM1kgz8rgxkHLiUV5y44nOa0hQ2HTaDsX3u4ZlPp 4ffn5tQdKd23l.nGltlonU2_mBFkLWUIfzDpgVXZ1fjIGFxh.gWjOXENO8IE v5CJfgd.haH5F9d1HxQ.1I1NvTKUaQRiat.go45RZWHGzUgT_yWgrAxKAmiN tGxc3m5QT1daq4GweybbuwplujoJUaB6vVuG5HtaVysGE_64RqB.b3jRnWBI psDSpQtgSMtFJ1_Q7RwwLGaMMZw.u7b4_ZpYQ49lep2ZtBCqj9DKLTN9weIl eJJYy3Iv68lpq8ZBywptSgb3s0QYnEzIX9IZpxwb3c3HkNVOQPDyG2REVdYi A357gCMJDWYD2bI8wXdTH.N._evgj4Z5yad5I.7KGLL4asJlmhc2fQWgfI.3 HqTRU29eoNH5bEvf3bW4M5KjewCMkfDCnxqup1XCKQcUENvEflK578SXOQwE D4cSdSJzg41k9uP88P0jE9enN X-Yahoo-SMTP: 7XGQHgGswBDgkLLWIBu6pqNs.6tUpXu5kYQqaG06DJ4lPfgH_WfGxPLi Received: from MJUPC (mike@86.134.219.88 with login) by smtp821.mail.ird.yahoo.com with SMTP; 24 Jul 2012 18:39:31 +0000 UTC Message-ID: From: "Mike Underhill" To: References: <500EB973.8080005@iup.uni-heidelberg.de> In-Reply-To: <500EB973.8080005@iup.uni-heidelberg.de> Date: Tue, 24 Jul 2012 19:37:53 +0100 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 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: Stefan As a long time 'lurker' on this LF group I am particularly interested in what orientation you plan for your low height 630m band dipole antenna and what azimuthal radiation pattern you find. A few years ago I did some work (on a contract) on low height, on-the-ground and underground antennas in the 1 to 10MHz region. The underground antenna was an end fed wire about 45m long in a 10cm 'land drain' in damp clay soil at a depth of about 45cm. (The wire was put in the drain using five sets of 10 drain rods.) These antennas radiated quite successfully with received and transmitted signals generally about 10 to 30dB down on a reference horizontal 83m loop at 15m height. Some of the tests were performed and winessed on a regular Sunday morning net on 3722kHz. [...] Content analysis details: (0.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [217.146.183.115 listed in list.dnswl.org] 0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid 0.0 UNPARSEABLE_RELAY Informational: message has unparseable relay lines X-Scan-Signature: 20fb97b64762a0bd80c12a4b2f6724b0 Subject: LF: Re: Pretests for the 630m band dipole Content-Type: text/plain; format=flowed; charset="ISO-8859-15"; reply-type=response Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.1 required=5.0 tests=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-SCORE: 0:2:500356192:93952408 X-AOL-SCOLL-URL_COUNT: 0 X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d010.1 ; domain : yahoo.com DKIM : fail x-aol-sid: 3039ac1d600b500eec1e7d48 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none Stefan As a long time 'lurker' on this LF group I am particularly interested in what orientation you plan for your low height 630m band dipole antenna and what azimuthal radiation pattern you find. A few years ago I did some work (on a contract) on low height, on-the-ground and underground antennas in the 1 to 10MHz region. The underground antenna was an end fed wire about 45m long in a 10cm 'land drain' in damp clay soil at a depth of about 45cm. (The wire was put in the drain using five sets of 10 drain rods.) These antennas radiated quite successfully with received and transmitted signals generally about 10 to 30dB down on a reference horizontal 83m loop at 15m height. Some of the tests were performed and winessed on a regular Sunday morning net on 3722kHz. Ocasionally broadcast signals in the 31m and 25m bands were found to be be stronger on the underground antenna than on the reference antenna. So local field strength measurements were then made just above ground on the under-ground and on-ground (dipole) antennas. A 35cm tuned loop antenna on an AOR hand-held scanning receiver was use as the field sensor. This could sense the field polarisation as well as the field strength. The conclusions were that such antennas "radiate and receive best from the ends with vertical polarisation". This was confirmed earler this year at the IET Ionnospheric Radio conference in York in a conversation with the conference chairman Les Barclay, G3HTF. He had found similar results some years earlier. The interesting question is why this might be so. The following is now offered as a possible explanation: Electric field lines above the antenna extend to a height that is a substantial fraction of (the square root of) a wavelength and terminating on the two ends of the antenna. This electric field creates displacement currents as half loops above the antenna from one end of the antenna to the other. The half loops of displacement current radiate with vertical polarisation with maxima in the direction of the ends of the dipole antenna. As the antenna height is raised the E-field lines and displacement currents become established below the antenna and above the ground. The currents are in the same direction as the currents above the antenna and so they start to cancel the loop radiation from the upper half loop(s) as the antenna is raised. At some critical height the conventional dipole mode takes over and the loop mode becomes suppressed. The critical height has been found to proportional to the square root of wavelength in accordance with the properties discovered for 'electromagnetic coupling'. (Measurements have been made for antennas at different heights and form the minimum horn size variation with frequency for the Goubau single wire transmission line.) >From measurements at higher HF frequencies I estimate the critical change-over height to be about 10 to 15 meters at 470kHz or 500kHz. At 136kHz these figures are increased by the square root of the freqency ratio, which is about 1.9. Real height of the antenna is important! Whether this hypothesis or suggested theory is correct depends on real and not simulated measurements. So you can guess the reason for my interest. Looking forward to your results with interest, so I can go back to lurking either with a warm glow of satisfaction or with a red face of embarrassment and disappointment. Mike - G3LHZ ----- Original Message ----- From: "Stefan Schäfer" To: Sent: Tuesday, July 24, 2012 4:04 PM Subject: LF: Pretests for the 630m band dipole > MF, > > This week i intend to start my tests with a full size dipole for the 630m > band. All the equipment for this /p is available now. > > Since the dipole is VERY close to ground (relative to Lambda) there will > be a capacitive component and the Z=R at resonance will be lower than 36 > Ohm of course. > I have just done some simulations in EZNEC and found that it is useful to > feed the dipole assymetrical, i.e. not in the center. The simulation > tells that a wire length of 315m will be necessary. The resonance > frequency does not change by different feed points. I hope this applies in > practice as well :-) > The electrical parameters will depend on the soil conductivity and epsilon > r, which i don't know exactly of course. But if the settings in the > simulation are reasonable, then there will be a real component of Z=R > (=resonance)of 46 Ohm. So i would not even need a transformer to match the > antenna to the PA. > > 85% means that one wire is "just" 47m. So if someone lives close to a > forest, there would be a chance to build such a TX antenna and run the > major part of the antenna outside the garden. Just a short rest has to be > inside the own property. For a 90% feed, R would be 96 Ohm. This could be > matched to 50 Ohm very easily and the shorter part of the antenna would > only be 31.5m... > > I have a bundle of old telephone wire (once found a 1800*0.4mm x 10m > length cable) and so i can connect several pieces in series for the test. > So i can make a table of measurements. The modified MFJ-259B antenna > analyzer will help, hopefully. > Looking forward to that test. > > Due to the permanent number of OP4 listening stations, this mode may > actually help to get an impression about the efficiency and directivity. > > 73, Stefan/DK7FC > > >