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[195.171.43.25]) by mx.google.com with ESMTP id ei7si3481362wid.17.2013.10.26.15.13.37 for ; Sat, 26 Oct 2013 15:13:38 -0700 (PDT) Received-SPF: neutral (google.com: 195.171.43.25 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) client-ip=195.171.43.25; Authentication-Results: mx.google.com; spf=neutral (google.com: 195.171.43.25 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) smtp.mail=owner-rsgb_lf_group@blacksheep.org Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1VaBo7-0006zI-Cp for rs_out_1@blacksheep.org; Sat, 26 Oct 2013 22:54:07 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1VaBo6-0006z9-IH for rsgb_lf_group@blacksheep.org; Sat, 26 Oct 2013 22:54:06 +0100 Received: from mailout10.t-online.de ([194.25.134.21]) by relay1.thorcom.net with esmtps (TLSv1:AES256-SHA:256) (Exim 4.77) (envelope-from ) id 1VaBo3-0004QV-JF for rsgb_lf_group@blacksheep.org; Sat, 26 Oct 2013 22:54:05 +0100 Received: from fwd22.aul.t-online.de (fwd22.aul.t-online.de ) by mailout10.t-online.de with smtp id 1VaBo1-0006l0-Ps; Sat, 26 Oct 2013 23:54:01 +0200 Received: from [87.174.160.187] (EI6pS6ZVQhr35lnZtik0AMRgdNifKAg5XaP3Pw6hkkVy4OT2CY8ggXqfo0MDc-Bgpy@[87.174.160.187]) by fwd22.t-online.de with esmtp id 1VaBo0-1qc5rc0; Sat, 26 Oct 2013 23:54:00 +0200 Message-ID: <526C375A.7060304@t-online.de> Date: Sat, 26 Oct 2013 23:42:50 +0200 From: Christoph Schumacher User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; de; rv:1.9.1.16) Gecko/20101125 Thunderbird/3.0.11 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <526ACC49.6030208@t-online.de> <29208E66335B49E08158AB7E38F57C7C@AGB> <526AD2A4.9060704@t-online.de> <0a4101ced1cd$728cbd10$57a63730$@comcast.net> In-Reply-To: <0a4101ced1cd$728cbd10$57a63730$@comcast.net> X-ID: EI6pS6ZVQhr35lnZtik0AMRgdNifKAg5XaP3Pw6hkkVy4OT2CY8ggXqfo0MDc-Bgpy X-TOI-MSGID: 8d36419d-848a-43a7-9977-6caa4ced6bc0 X-Spam-Score: -0.4 (/) 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: Hi Graham, Warren, Bob, Rik, Jim thanks for your comments. What I found (by chance) is a series resonance in the impedance spectrum of solenoid air coils, a little underneath the high impedance parallel resonance. The series resonance could derive from the coils main inductance and its capacity to the surrounded electric field. But it fits only very vague. However on that frequency the coil is a very efficient radiator especially related to its shape. Stimulating the coil on the high impedance parallel resonance does not effect any far field radiation. [...] Content analysis details: (-0.4 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [194.25.134.21 listed in list.dnswl.org] -0.4 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain 0.0 HTML_MESSAGE BODY: HTML included in message 0.0 UNPARSEABLE_RELAY Informational: message has unparseable relay lines X-Scan-Signature: 986df75162af045670df2f67fcfcb92a Subject: Re: LF: air solenoids Content-Type: multipart/alternative; boundary="------------060501090403040406090601" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: * X-Spam-Status: No, hits=1.0 required=5.0 tests=HTML_40_50,HTML_MESSAGE, HTML_TITLE_EMPTY 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 Status: O X-Status: X-Keywords: X-UID: 3372 This is a multi-part message in MIME format. --------------060501090403040406090601 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Hi Graham, Warren, Bob, Rik, Jim thanks for your comments. What I found (by chance) is a series resonance in the impedance spectrum of solenoid air coils, a little underneath the high impedance parallel resonance. The series resonance could derive from the coils main inductance and its capacity to the surrounded electric field. But it fits only very vague. However on that frequency the coil is a very efficient radiator especially related to its shape. Stimulating the coil on the high impedance parallel resonance does not effect any far field radiation. For instance: my lf coil for 135kHz has app. 5mH inductance, 42cm (17 inch) diameter, 27cm (11 inch) length. The high impedance parallel resonance is 600kHz and the low impedance series resonance is 500kHz. The resistance on that frequency is 180 Ohm and the SWR=2 bandwidth is 2kHz. On 500kHz the coil is a very efficient radiator related to its mechanical length of lambda/500ppm. Using an input of app. 7mW (DDS-gen.) into that coil I could read cw code at 1km distance via active antenna on my car roof (maybe 6dB SNR). I become suspicious on whether the radiation resistance model is still valid for such a tiny radiator. It is not my intention to introduce a new lf radiator because at that resonance the voltage across the coil must be gigantic. I only would like to understand the physics. Do you have an idea? Best regards chris dl7saq Am 25.10.2013 23:58, schrieb hvanesce: > > Chris, > > I'll second Warren's motion.The radiation efficiency of a 100-turn, > 1-meter diameter solenoid (of any reasonable length/diameter ratio) at > 100kHz is in the hundreds of nano-ohms, i.e. a very difficult starting > point with respect to dissipative losses directly and indirectly > associated with wire resistance and coil inductance. Radiation > resistance of a solenoid scales with turns squared, but with > resistance scaling directly with turns, large numbers of turns is not > a reasonable approach for practical wire diameters. > > The reactive field (induction field), which comprises most of the > field (for a solenoid that is presumably a small fraction of a > wavelength) does not suffer low efficiency, but reactive field > strength falls by a factor of eight for (practically speaking) for > every doubling of distance, starting near the aperture boundary. The > reactive field strength 1km from a 1-meter diameter solenoid (properly > oriented away from the null) would be 1E-9 that of the field strength > near the aperture boundary. > > Regards, > > Jim AA5BW > > *From:* owner-rsgb_lf_group@blacksheep.org > [mailto:owner-rsgb_lf_group@blacksheep.org] *On Behalf Of *Warren Ziegler > *Sent:* Friday, October 25, 2013 3:50 PM > *To:* rsgb_lf_group > *Subject:* Re: LF: air solenoids > > Christoph, > > A while back someone on the US longwave reflector posted the > result of an experiment. They took a receiver to the site of a high > power Tesla coil operating at LF, I believe it was being driven at > 175kHz. they expected to hear it at some distance but were surprised > to find out they could only hear the Tesla coil at very short > distances. It seems that a coil by itself is an extremely poor > radiator at LF! It is unknown to me if there was any earth connection > to the Tesla coil, perhaps only through the mains connection. > > 73 Warren > > On Fri, Oct 25, 2013 at 4:20 PM, Christoph Schumacher > > wrote: > > no, cylindrical coils > > Am 25.10.2013 22:11, schrieb Graham: > > toroidal ? > > *From:* Christoph Schumacher > > *Sent:* Friday, October 25, 2013 8:53 PM > > *To:* rsgb_lf_group@blacksheep.org > > > *Subject:* LF: air solenoids > > Dear all, > is there anyone who was concerned sometime with the self radiating > properties of single layer air solenoids without any piece of > antenna wire? > > 73 dl7saq, Chris > > > > -- > 73 Warren K2ORS > WD2XGJ > WD2XSH/23 > WE2XEB/2 > WE2XGR/1 > --------------060501090403040406090601 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Hi Graham, Warren, Bob, Rik, Jim
thanks for your comments. What I found (by chance) is a series resonance in the impedance spectrum of solenoid air coils, a little underneath the high impedance parallel resonance. The series resonance could derive from the coils main inductance and its capacity to the surrounded electric field. But it fits only very vague. However on that frequency the coil is a very efficient radiator especially related to its shape. Stimulating the coil on the high impedance parallel resonance does not effect any far field radiation.

For instance: my lf coil for 135kHz has app. 5mH inductance, 42cm (17 inch) diameter, 27cm (11 inch) length. The high impedance parallel resonance is 600kHz and the low impedance series resonance is 500kHz. The resistance on that frequency is 180 Ohm and the SWR=2 bandwidth is 2kHz. On 500kHz the coil is a very efficient radiator related to its mechanical length of lambda/500ppm. Using an input of app. 7mW (DDS-gen.) into that coil I could read cw code at 1km distance via active antenna on my car roof (maybe 6dB SNR).

I become suspicious on whether the radiation resistance model is still valid for such a tiny radiator. It is not my intention to introduce a new lf radiator because at that resonance the voltage across the coil must be gigantic. I only would like to understand the physics. Do you have an idea?

Best regards
chris dl7saq




Am 25.10.2013 23:58, schrieb hvanesce:

Chris,

 

I’ll second Warren’s motion.The radiation efficiency of a 100-turn, 1-meter diameter solenoid (of any reasonable length/diameter ratio) at 100kHz is in the hundreds of nano-ohms, i.e. a very difficult starting point with respect to dissipative losses directly and indirectly associated with wire resistance and coil inductance. Radiation resistance of a solenoid scales with turns squared, but with resistance scaling directly with turns, large numbers of turns is not a reasonable approach for practical wire diameters.

 

The reactive field (induction field), which comprises most of the field (for a solenoid that is presumably a small fraction of a wavelength) does not suffer low efficiency, but reactive field strength falls by a factor of eight for (practically speaking) for every doubling of distance, starting near the aperture boundary. The reactive field strength 1km from a 1-meter diameter solenoid (properly oriented away from the null) would be 1E-9 that of the field strength near the aperture boundary.

 

Regards,

 

Jim AA5BW

 

From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Warren Ziegler
Sent: Friday, October 25, 2013 3:50 PM
To: rsgb_lf_group
Subject: Re: LF: air solenoids

 

Christoph,

    A while back someone on the US longwave reflector posted the result of an experiment. They took a receiver to the site of a high power Tesla coil operating at LF, I believe it was being driven at 175kHz. they expected to hear it at some distance but were surprised to find out they could only hear the Tesla coil at very short distances. It seems that a coil by itself is an extremely poor radiator at LF!  It is unknown to me if there was any earth connection to the Tesla coil, perhaps only through the mains connection.

 

73 Warren

 

 

 

On Fri, Oct 25, 2013 at 4:20 PM, Christoph Schumacher <chris-schum@t-online.de> wrote:

no, cylindrical coils

Am 25.10.2013 22:11, schrieb Graham:

toroidal ?

 

Sent: Friday, October 25, 2013 8:53 PM

Subject: LF: air solenoids

 

Dear all,
is there anyone who was concerned sometime with the self radiating properties of single layer air solenoids without any piece of antenna wire?

73 dl7saq, Chris

 



 

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

 


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