Re: Need Near Field equations problems [Archive]

Richard Clark

Nov14-04, 06:26 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Fri, 12 Nov 2004 19:07:34 +0000 (UTC), curiousjohn4@yahoo.com\n(curiousjohn4) wrote:\n> In fact, there was significant induced voltage from a very long wire.\n\nHi OM,\n\nYou are treading water here. There is more than radiation at work\nvery close to an antenna. Consider your own language above: Induction\n(or even capacitive coupling).\n\n73\'s\nRichard Clark, KB7QHC\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Fri, 12 Nov 2004 19:07:34 +0000 (UTC), curiousjohn4@yahoo.com
(curiousjohn4) wrote:
> In fact, there was significant induced voltage from a very long wire.

Hi OM,

You are treading water here. There is more than radiation at work
very close to an antenna. Consider your own language above: Induction
(or even capacitive coupling).

73's
Richard Clark, KB7QHC

Roy Lewallen

Nov14-04, 11:59 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>curiousjohn4 wrote:\n\n\n> Could someone please provide a correct near field equation that a\n> computer programmer can understand? I\'m using the following equation\n> in a simple simulation but it\'s not working in all cases.\n>\n> E = a * sin(theta) * q / ( 4 * pi * e * c^2 * r )\n\n\n\nI don\'t know where you got that equation, but I\'m not surprised it\'s not\ngiving the right answer. In the near field, there are components\ninversely proportional to r, r^2, and r^3. The equations are too complex\nto easily write in ASCII, and the terms require some definition. But you\ncan find the relevant equations in Jordan & Balmain, _Electromagnetic\nWaves and Radiating Systems_, eq. 10-41 and 10-42; Kraus,\n_Electromagnetics_, eq. 13-49 and 13-50; Johnk, _Engineering\nElectromagnetic Fields and Waves_, eq. 11-41a and 11-41b; or most other\nelectromagnetics and some antenna texts. Note that two equations are\ngiven, one for the radial component and another for the circular (theta)\ncomponent, which decay at different rates as the distance from the\ncurrent element increases.\n\nRoy Lewallen, W7EL\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>curiousjohn4 wrote:

> Could someone please provide a correct near field equation that a
> computer programmer can understand? I'm using the following equation
> in a simple simulation but it's not working in all cases.
>
> E = a * sin(\theta) * q / ( 4 * \pi * e * c^2 * r )

I don't know where you got that equation, but I'm not surprised it's not
giving the right answer. In the near field, there are components
inversely proportional to r, r^2, and r^3. The equations are too complex
to easily write in ASCII, and the terms require some definition. But you
can find the relevant equations in Jordan & Balmain, _Electromagnetic
Waves and Radiating Systems_, eq. 10-41 and 10-42; Kraus,
_Electromagnetics_, eq. 13-49 and 13-50; Johnk, _Engineering
Electromagnetic Fields and Waves_, eq. 11-41a and 11-41b; or most other
electromagnetics and some antenna texts. Note that two equations are
given, one for the radial component and another for the circular (\theta)
component, which decay at different rates as the distance from the
current element increases.

Roy Lewallen, W7EL

Frank

Nov16-04, 02:16 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>"Richard Clark" <kb7qhc@comcast.net> wrote in message\nnews:r24ap05qqdaa1ge6vdf4ioibqhvjf378tk@4 ax.com...\n> On Fri, 12 Nov 2004 19:07:34 +0000 (UTC), curiousjohn4@yahoo.com\n> (curiousjohn4) wrote:\n>> In fact, there was significant induced voltage from a very long wire.\n>\n> Hi OM,\n>\n> You are treading water here. There is more than radiation at work\n> very close to an antenna. Consider your own language above: Induction\n> (or even capacitive coupling).\n>\n> 73\'s\n> Richard Clark, KB7QHC\n\nI think Richard has hit the nail on the head. I wish calculation of\nelectromagnetic fields could be reduced to a simple equation. Any\nundergraduate text on electromagnetics barely scratches the surface. I\nsuggest you check the site at www.nec2.org and download the .pdf version of\nthe "NEC Program Description -- Theory". Gives an overview of "Method of\nMoments". As a foundation Kraus\' Electromagnetics may help, and is\navailable used (and cheap) at www.bn.com. Also at the same site a reprint\nof "Field Computation by Moment Methods" by Roger F. Harrington can be\nobtained for \\$33.50. Then there is the "Finite Element" method as used by\n"Ansoft\'s" HFSS".\n\n\nRegards,\n\nFrank\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Richard Clark" <kb7qhc@comcast.net> wrote in message
news:r24ap05qqdaa1ge6vdf4ioibqhvjf378tk@4ax.com...
> On Fri, 12 Nov 2004 19:07:34 +0000 (UTC), curiousjohn4@yahoo.com
> (curiousjohn4) wrote:
>> In fact, there was significant induced voltage from a very long wire.
>
> Hi OM,
>
> You are treading water here. There is more than radiation at work
> very close to an antenna. Consider your own language above: Induction
> (or even capacitive coupling).
>
> 73's
> Richard Clark, KB7QHC

I think Richard has hit the nail on the head. I wish calculation of
electromagnetic fields could be reduced to a simple equation. Any
undergraduate text on electromagnetics barely scratches the surface. I
suggest you check the site at www.nec2.org and download the .pdf version of
the "NEC Program Description -- Theory". Gives an overview of "Method of
Moments". As a foundation Kraus' Electromagnetics may help, and is
available used (and cheap) at www.bn.com. Also at the same site a reprint
of "Field Computation by Moment Methods" by Roger F. Harrington can be
obtained for $33.50. Then there is the "Finite Element" method as used by
"Ansoft's" HFSS".

Regards,

Frank