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References: <67c4e86218e0fe1d934327099833d80e@email.freenet.de> <5015CB44.4060800@iup.uni-heidelberg.de> <501728EF.60401@iup.uni-heidelberg.de> <501AA1EF.1070506@iup.uni-heidelberg.de>
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Content preview: Thank you Stefan for this interesting experiment and report.
Here are a couple of thoughts I have discussed with Stefan, and which I would
like to share with the group. Regarding the decrease of the resonance frequency
close to earth: The wire is a line with distributed capacitance and inductance.
If you would bring a halfwave line in close proximity to a perfectly conducting
plane, the capacitance would be increased. But at the same time the inductance
would decrease, as the magnetic flux would be confined by the smaller gap
between the wire and the ground plane. So the wave impedance would go down
but the resonance frequency would remain nearly unchanged. [...]
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Subject: Re: LF: MF: 630m band dipole tests today
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Thank you Stefan for this interesting experiment and report. Here are a =
couple of thoughts I have discussed with Stefan, and which I would like =
to share with the group.
Regarding the decrease of the resonance frequency close to earth: The =
wire is a line with distributed capacitance and inductance. If you would =
bring a halfwave line in close proximity to a perfectly conducting =
plane, the capacitance would be increased. But at the same time the =
inductance would decrease, as the magnetic flux would be confined by the =
smaller gap between the wire and the ground plane. So the wave impedance =
would go down but the resonance frequency would remain nearly unchanged. =
A couple of meters above real ground, the capacitance would still be =
increased as long as its impedance is high compared to that of the soil. =
However the magnetic fields will penetrate the soil to some depth, so =
the effect on the inductance is much less. Thus the resonant frequency =
will go down at low height.
However when the wire is actually laid on the ground, the capacitance =
becomes so large that its impedance falls below the ohmic ground =
resistance. So then you will end up with a nonresonant nearly real =
impedance - just what Stefan observed.
Regarding the radiation pattern: An low dipole, oriented eg. in the E-W =
direction, would be expected to have three distinct modes of radiation:
- a high angle skywave ("Near Vertical Incidence Skywave"), with more or =
less omnidirectional pattern, and the E-field vector polarized E-W,
- a horizontally polarized low angle radiation, broadside to N and S. =
However this would be heavily attenuated by the ground acting as a short =
circuit, and would not be able to develop into a propagating ground =
wave, =20
- a vertically polarized groundwave to the E and W, generated by an =
earth loop formed by the wire and the subsurface return current. This is =
the same mechanism as in the VLF earth-antenna experiments, only with =
the galvanic end contacts replaced by capacitive coupling. I believe =
that this mode enabled the daytime QSO between Stefan and myself, 180 km =
due east of him. This axial radiation would of course not be present for =
a free space dipole.
Best 73,
Markus (DF6NM).
From: Stefan Sch=C3=A4fer=20
Sent: Thursday, August 02, 2012 5:51 PM
To: rsgb_lf_group@blacksheep.org=20
Subject: Re: LF: MF: 630m band dipole tests today
MF,=20
Here is my report of the MF dipole experiment of last saturday: =
https://dl.dropbox.com/u/19882028/MF/A%20full%20size%20dipole%20for%20the=
%20630%20m%20band.pdf
73, Stefan/DK7FC
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Content-Type: text/html;
charset="utf-8"
Content-Transfer-Encoding: quoted-printable
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=3DContent-Type content=3Dtext/html;charset=3Dutf-8>
<META content=3D"MSHTML 6.00.6000.17110" name=3DGENERATOR></HEAD>
<BODY id=3DMailContainerBody=20
style=3D"PADDING-RIGHT: 10px; PADDING-LEFT: 10px; PADDING-TOP: 15px" =
text=3D#000000=20
bgColor=3D#ffffff leftMargin=3D0 topMargin=3D0 CanvasTabStop=3D"true"=20
name=3D"Compose message area">
<DIV><FONT face=3DArial size=3D2>Thank you Stefan for this interesting =
experiment=20
and report. </FONT><FONT face=3DArial size=3D2>Here are a couple of =
thoughts I have=20
discussed with Stefan, and which I would like to share with the=20
group.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Regarding the decrease of the resonance =
frequency=20
close to earth: The wire is a line with =
distributed capacitance and=20
inductance. If you would bring a halfwave line in close proximity =
to a=20
perfectly conducting plane, the capacitance would be increased. But at =
the same=20
time the inductance would decrease, as the magnetic flux would be =
confined=20
by the smaller gap between the wire and the ground plane. So the =
wave=20
impedance would go down but the resonance frequency would =
remain=20
nearly unchanged. </FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT><FONT face=3DArial =
size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>A couple of meters above real ground, =
the=20
capacitance would still be increased as long as its =
impedance is=20
high compared to that of the soil. However the magnetic fields=20
will penetrate the soil to some depth, so the effect on the =
inductance is=20
much less. Thus the resonant frequency will go down at low =
height.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>However when the wire is actually =
laid on the=20
ground, the capacitance becomes so large that its impedance falls below=20
the ohmic ground resistance. So then you will end up with a =
nonresonant=20
nearly real impedance - just what Stefan observed.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Regarding the radiation =
pattern: An low=20
dipole, oriented eg. in the E-W direction, would be expected to have=20
three distinct modes of radiation:</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>- a high angle skywave ("Near =
Vertical=20
Incidence Skywave"), with more or less omnidirectional pattern, and the =
E-field=20
vector polarized E-W,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>- a horizontally polarized low angle =
radiation,=20
broadside to N and S. However this would be heavily attenuated by the =
ground=20
acting as a short circuit, and would not be able to develop into a=20
propagating ground wave, </FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>- a vertically polarized groundwave to =
the E and W,=20
generated by an earth loop formed by the wire and the =
subsurface=20
return current. This is the same mechanism as in the VLF earth-antenna=20
experiments, only with the galvanic end contacts replaced by capacitive=20
coupling. I believe that this mode enabled the daytime QSO between =
Stefan and=20
myself, 180 km due east of him. This axial radiation would of course not =
be=20
present for a free space dipole.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT><FONT face=3DArial =
size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Best 73,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Markus (DF6NM).</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT><FONT face=3DArial =
size=3D2></FONT><FONT=20
face=3DArial size=3D2></FONT><FONT face=3DArial size=3D2></FONT><FONT =
face=3DArial=20
size=3D2></FONT><FONT face=3DArial size=3D2></FONT><FONT face=3DArial=20
size=3D2></FONT><FONT face=3DArial size=3D2></FONT><FONT face=3DArial=20
size=3D2></FONT><FONT face=3DArial size=3D2></FONT><BR></DIV>
<DIV style=3D"FONT: 10pt Tahoma">
<DIV style=3D"BACKGROUND: #f5f5f5">
<DIV style=3D"font-color: black"><B>From:</B> <A=20
title=3D"mailto:Stefan.Schaefer@iup.uni-heidelberg.de STRG + =
Klicken, um Verkn=C3=BCpfung zu folgen"=20
href=3D"mailto:Stefan.Schaefer@iup.uni-heidelberg.de">Stefan =
Sch=C3=A4fer</A> </DIV>
<DIV><B>Sent:</B> Thursday, August 02, 2012 5:51 PM</DIV>
<DIV><B>To:</B> <A=20
title=3D"mailto:rsgb_lf_group@blacksheep.org STRG + Klicken, um =
Verkn=C3=BCpfung zu folgen"=20
href=3D"mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blacksheep.org=
</A>=20
</DIV>
<DIV><B>Subject:</B> Re: LF: MF: 630m band dipole tests =
today</DIV></DIV></DIV>
<DIV><FONT face=3DArial size=3D2></FONT><FONT face=3DArial =
size=3D2></FONT><FONT=20
face=3DArial size=3D2></FONT><FONT face=3DArial =
size=3D2></FONT><BR></DIV>
<DIV>MF, <BR><BR>Here is my report of the MF dipole experiment of last =
saturday:=20
<A class=3Dmoz-txt-link-freetext=20
title=3D"https://dl.dropbox.com/u/19882028/MF/A%20full%20size%20dipole%20=
for%20the%20630%20m%20band.pdf STRG + Klicken, um Verkn=C3=BCpfung =
zu folgen"=20
href=3D"https://dl.dropbox.com/u/19882028/MF/A%20full%20size%20dipole%20f=
or%20the%20630%20m%20band.pdf">https://dl.dropbox.com/u/19882028/MF/A%20f=
ull%20size%20dipole%20for%20the%20630%20m%20band.pdf</A><BR><BR>73,=20
Stefan/DK7FC</DIV>
<DIV> </DIV></BODY></HTML>
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