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From: Markus Vester <markusvester@aol.com>
Message-Id: <8D09D527697128F-2298-36AF9@Webmail-d108.sysops.aol.com>
Date: Tue, 22 Oct 2013 11:28:16 -0400 (EDT)
Subject: Re: LF: 74.5493 instead...(1of2)
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Dex,
=C2=A0
antennas are getting on in years, and so are we ;-) The one good thing abou=
t tree supports is that they grow taller with age: The pine tree supporting=
 my southern top load leg has grown from 6 to 11 meters since I first attac=
hed a string in 1999.=20
http://maps.google.de/maps?ll=3D49.4158,11.1350&z=3D21=20
Recently one of my neighbours has given hints about shading and possible pr=
uning, which I hope to be able to divert for a while.
=C2=A0
Regarding ERP on 74 kHz: For a voltage limited E-field antenna, at half fre=
quency you have to reduce input power until you have halved the current. In=
 conjunction with the quarter radiation resistance, ERP would go down by a =
factor of 16! At VLF this is very severe: My small Marconi antenna, which c=
an barely radiate 1 W ERP at 136 kHz, drops to 10 microwatts at 9 kHz. A si=
milar same scaling also applies to loops driven at constant current.
=C2=A0
In addition, at lower frequencies trees around an E-field antenna shunt a l=
arger portion of the displacement current to ground, due to the ratio of ca=
pacitive versus ohmic impedances. From my experience, this degradation disa=
ppears only during deep frost when trunks apparently become completely dry.
=C2=A0
Still hope to catch your 74 kHz beacon one of these days. However I suspect=
 that the DCF77 noise may not be completely neglegible here, even between 1=
 Hz maxima. This might explain some of the perceived reception deficits in =
Germany, versus England and Holland.=20
=C2=A0
Best wishes,
Markus (DF6NM)

=C2=A0
-----Urspr=C3=BCngliche Mitteilung-----=20
Von: Dexter McIntyre W4DEX &lt;dexter.mc@gmail.com&gt;
An: rsgb_lf_group &lt;rsgb_lf_group@blacksheep.org&gt;
Verschickt: Mo, 21 Okt 2013 10:52 pm
Betreff: Re: LF: 74.5493 instead...(1of2)


I've been running /5 from sundown to sunup.  200 watts leaving the =20
 shack.  Perhaps the signal will improve when the oak trees under the top =
=20
 hat wires are bare.  The leaves are just now beginning to fall.   Most =20
 of the several hundred feet of top hat wires run over a combination of =20
 oak and pine trees.  I've often wondered if my antenna would be more =20
 efficient with more loading instead of having the top hat.  I'll =20
 probably never know because it would be way to much work to find out.  =20
 The antenna has been in use for 8 years.  I may find out when the top =20
 hat wire fails because I doubt I'm now able to replace them.=20
 =20
 Nice to at least see those traces Mike.=20
 =20
 Dex=20
 =20
 ...


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<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt"><FONT colo=
r=3Dblack face=3Darial></FONT><SPAN style=3D"DISPLAY: inline-block" content=
Editable=3Dfalse></SPAN><FONT color=3Dblack face=3Darial></FONT><SPAN style=
=3D"DISPLAY: inline-block"></SPAN>Dex,</div>


<div id=3DAOLMsgPart_1_c7467d5e-1bd7-4454-9905-107bcbc8d794>

<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">&nbsp;</di=
v>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">antennas a=
re getting on in years, and so are we ;-) The one good thing about tree sup=
ports is that they grow taller with age: The pine tree supporting my southe=
rn top load leg has grown from 6 to 11 meters since I first attached a stri=
ng in 1999. </div>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt"><A href=3D=
"http://maps.google.de/maps?ll=3D49.4158,11.1350&amp;z=3D21" target=3D_blan=
k>http://maps.google.de/maps?ll=3D49.4158,11.1350&amp;z=3D21</A> </div>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">Recently o=
ne of my neighbours has given hints about shading and possible pruning, whi=
ch I hope to be able to divert for a while.</div>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">&nbsp;</di=
v>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">Regarding =
ERP on 74 kHz: For a voltage limited E-field antenna, at half frequency you=
 have to reduce input power until you have halved the current. In conjuncti=
on with the quarter radiation resistance, ERP would go down by a factor of =
16! At VLF this is very severe: My small Marconi antenna, which can barely =
radiate 1 W ERP at 136 kHz, drops to 10 microwatts at 9 kHz. A similar same=
 scaling also applies to loops driven at constant current.</div>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">&nbsp;</di=
v>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">In additio=
n, at lower frequencies trees around an E-field antenna shunt a larger port=
ion of the displacement current to ground, due to the ratio of capacitive v=
ersus ohmic impedances. From my experience, this degradation disappears onl=
y during deep frost when trunks apparently become completely dry.</div>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">&nbsp;</di=
v>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">Still hope=
 to catch your 74 kHz beacon one of these days. However I suspect that the =
DCF77 noise may not be completely neglegible here, even between 1 Hz maxima=
. This might explain some of the perceived reception deficits in Germany, v=
ersus England and Holland. </div>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">&nbsp;</di=
v>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt">Best wishe=
s,<br>
Markus (DF6NM)</div>


<div style=3D"FONT-FAMILY: arial; COLOR: black; FONT-SIZE: 10pt"><br>
&nbsp;</div>


<div>-----Urspr=C3=BCngliche Mitteilung----- <br>
Von: Dexter McIntyre W4DEX &lt;<A href=3D"mailto:dexter.mc@gmail.com">dexte=
r.mc@gmail.com</A>&gt;<br>
An: rsgb_lf_group &lt;<A href=3D"mailto:rsgb_lf_group@blacksheep.org">rsgb_=
lf_group@blacksheep.org</A>&gt;<br>
Verschickt: Mo, 21 Okt 2013 10:52 pm<br>
Betreff: Re: LF: 74.5493 instead...(1of2)<br>
<br>
</div>


<div style=3D"BACKGROUND-COLOR: #fff; MARGIN: 0px; FONT-FAMILY: Tahoma, Ver=
dana, Arial, Sans-Serif; COLOR: #000; FONT-SIZE: 12px" id=3Daolmail_AOLMsgP=
art_0_732e1d94-9248-470d-bcdf-f24ffa4ac6f4><br>
<PRE style=3D"FONT-SIZE: 9pt"><TT>I've been running /5 from sundown to sunu=
p.  200 watts leaving the  <br>
 shack.  Perhaps the signal will improve when the oak trees under the top  =
<br>
 hat wires are bare.  The leaves are just now beginning to fall.   Most  <b=
r>
 of the several hundred feet of top hat wires run over a combination of  <b=
r>
 oak and pine trees.  I've often wondered if my antenna would be more  <br>
 efficient with more loading instead of having the top hat.  I'll  <br>
 probably never know because it would be way to much work to find out.   <b=
r>
 The antenna has been in use for 8 years.  I may find out when the top  <br=
>
 hat wire fails because I doubt I'm now able to replace them. <br>
  <br>
 Nice to at least see those traces Mike. <br>
  <br>
 Dex <br>
  <br>
 ...</TT></PRE></div>
</div>

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