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Date: Sat, 26 Jun 2010 17:05:01 +0100
Message-ID: <AANLkTikRKnu3GJ8o9-wvXUFwOlSUtUwVQe3oZ8KuU6F0@mail.gmail.com>
From: Roger Lapthorn <rogerlapthorn@gmail.com>
To: rsgb_lf_group@blacksheep.org
DomainKey-Status: good (testing) 
Subject: Re: VLF: Near field boundary (Re DK7FC's DFCW600 8.97kHz transmission 
	NOW)
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Dear Markus,

Maths, EM theory and Maxwell's equations were not my strong points at all,
so I'm struggling to understand what you are saying (this is my weakness=
 and
not a weakness in your explanation).

I *think* you are saying that at the sort of distances being achieved by
Stefan (~5.2kms) , the H-field component would be slightly weaker than the
E-field, so an E-field probe would result in marginally better reception?=
 At
greater distances, the difference would not be significant.

Markus, if you have time, I have some more questions:

   - We think Stefan's earth electrode signals are "making the hop" withou=
t
   being aided by buried utilities. Is there any way of confirming this fr=
om
   the field strengths measured using both H and E-field antennas?
   - Is Stefan likely to get much further using his earth electrode
   antenna?  i.e, by radiation
   - Do you know (from theory) how a 300m high Marconi vertical and a 300m
   long earth electrode antenna are likely to compare as antennas *radiati=
ng
   *a far field signal?

Thank you everyone who has been contributing to the discussion and practic=
al
experimentation below 9kHz. It is totally absorbing. I just wish I was mor=
e
brainy!

73s
Roger G3XBM


On 26 June 2010 16:11, Markus Vester <markusvester@aol.com> wrote:

> Dear Roger, Stefan,
>
> actually, with all else equal, the earth antenna signal would have been=
 3
> dB
> weaker on a loop receiver! This is due to a small effect at the near fie=
ld
> boundary, mentioned by Jacek two weeks ago.
>
> The field equations for a small electrical dipole are
>
> E(r) =3D il *Zo / 4pi * (jk)=B2 * [1/(jkr)=B3 + 1/(jkr)=B2 + 1/(jkr)] *=
 exp(-jkr)
> H(r) =3D il / 4pi * (jk)=B2 * [1/(jkr)=B2 + 1/(jkr)] * exp(-jkr)
>
> with E and H being the transverse fields in the equatorial plane,
> il =3D source moment =3D current times effective height,
> Zo =3D 377 ohm,
> j =3D imaginary unit (note that j=B3 =3D -j)
> r =3D distance from the antenna,
> k =3D wave number =3D omega/c =3D 2pi/lambda.
>
> The appended image shows the fields around a one meter high Marconi driv=
en
> by one ampere, thus radiating 1.42 uW (EMRP) at 9 kHz. The E field (red
> line) is dominant near the antenna, but has a slight ditch at 5.3 km. He=
re
> the electrostatic r^-3 and the radiative r^-1 components cancel, and onl=
y
> the inductive r^-2  component is left. On the other hand, the H-field (b=
lue
> line, scaled to E-field units by 377 ohms) does not have a r^-3 componen=
t
> in
> the first place, and no cancellation occurs. In the^far field, E and sca=
led
> H are of course asymptotically equal, with magnitudes proportional to il=
,
> frequency (jk) and r^-1.
>
> For the dual case of a magnetic source (eg. earth antenna) of same ERP,=
 the
> roles are simply interchanged, so red would be magnetic, and blue electr=
ic
> field.
>
> The noise level indicated by the dotted line (5 dBuV/m/sqrtHz) was measu=
red
> ten years ago and is probably about 10 dB too low. In case you prefer
> magnetic units (picotesla), the conversion is 1 V/m =3D 3.33 nT, or 0 dB=
uV/m
> =3D -70.5 dBpT.
>
> Well done, Stefan!
>
> Kind regards,
> Markus (DF6NM)
>
>
> From: Roger Lapthorn
> Sent: Saturday, June 26, 2010 12:52 PM
> To: rsgb_lf_group@blacksheep.org
> Subject: Re: LF: DK7FC's DFCW600 8.97kHz transmission NOW
>
> Stefan,
>
> I wonder how strong the signal would have been on a RX loop rather than=
 the
> E-field probe? This would be worth checking.
>
> 73s
> Roger G3XBM
>
>
> On 26 June 2010 11:50, Roger Lapthorn <rogerlapthorn@gmail.com> wrote:
>
> 73 - the first message proper on the Dreamer's Band Stefan?
>
> Kind regards
> Roger G3XBM
>



--=20
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM    GQRP 1678      ISWL G11088

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Dear Markus,<br><br>Maths, EM theory and Maxwell&#39;s equations were not=
 my strong points at all, so I&#39;m struggling to understand what you are=
 saying (this is my weakness and not a weakness in your explanation).<br><=
br>
I <i>think</i> you are saying that at the sort of distances being achieved=
 by Stefan (~5.2kms) , the H-field component would be slightly weaker than=
 the E-field, so an E-field probe would result in marginally better recept=
ion? At greater distances, the difference would not be significant.<br>
<br>Markus, if you have time, I have some more questions:<br><ul><li>We th=
ink Stefan&#39;s earth electrode signals are &quot;making the hop&quot; wi=
thout being aided by=20
buried utilities. Is there any way of confirming this from the field=20
strengths measured using both H and E-field antennas?</li><li>Is Stefan li=
kely to get much further using his earth electrode antenna?=A0 i.e, by rad=
iation<br></li><li>Do you know (from theory) how a 300m high Marconi verti=
cal and a 300m long earth electrode antenna are likely to compare as anten=
nas <i>radiating </i>a far field signal?</li>
</ul>Thank you everyone who has been contributing to the discussion and pr=
actical experimentation below 9kHz. It is totally absorbing. I just wish=
 I was more brainy!<br><br>73s<br>Roger G3XBM<br>=A0 <br><br><div class=3D=
"gmail_quote">
On 26 June 2010 16:11, Markus Vester <span dir=3D"ltr">&lt;<a href=3D"mail=
to:markusvester@aol.com">markusvester@aol.com</a>&gt;</span> wrote:<br><bl=
ockquote class=3D"gmail_quote" style=3D"margin: 0pt 0pt 0pt 0.8ex; border-=
left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
Dear Roger, Stefan,<br>
<br>
actually, with all else equal, the earth antenna signal would have been 3=
 dB<br>
weaker on a loop receiver! This is due to a small effect at the near field=
<br>
boundary, mentioned by Jacek two weeks ago.<br>
<br>
The field equations for a small electrical dipole are<br>
<br>
E(r) =3D il *Zo / 4pi * (jk)=B2 * [1/(jkr)=B3 + 1/(jkr)=B2 + 1/(jkr)] * ex=
p(-jkr)<br>
H(r) =3D il / 4pi * (jk)=B2 * [1/(jkr)=B2 + 1/(jkr)] * exp(-jkr)<br>
<br>
with E and H being the transverse fields in the equatorial plane,<br>
il =3D source moment =3D current times effective height,<br>
Zo =3D 377 ohm,<br>
j =3D imaginary unit (note that j=B3 =3D -j)<br>
r =3D distance from the antenna,<br>
k =3D wave number =3D omega/c =3D 2pi/lambda.<br>
<br>
The appended image shows the fields around a one meter high Marconi driven=
<br>
by one ampere, thus radiating 1.42 uW (EMRP) at 9 kHz. The E field (red<br=
>
line) is dominant near the antenna, but has a slight ditch at 5.3 km. Here=
<br>
the electrostatic r^-3 and the radiative r^-1 components cancel, and only<=
br>
the inductive r^-2 =A0component is left. On the other hand, the H-field (b=
lue<br>
line, scaled to E-field units by 377 ohms) does not have a r^-3 component=
 in<br>
the first place, and no cancellation occurs. In the^far field, E and scale=
d<br>
H are of course asymptotically equal, with magnitudes proportional to il,<=
br>
frequency (jk) and r^-1.<br>
<br>
For the dual case of a magnetic source (eg. earth antenna) of same ERP, th=
e<br>
roles are simply interchanged, so red would be magnetic, and blue electric=
<br>
field.<br>
<br>
The noise level indicated by the dotted line (5 dBuV/m/sqrtHz) was measure=
d<br>
ten years ago and is probably about 10 dB too low. In case you prefer<br>
magnetic units (picotesla), the conversion is 1 V/m =3D 3.33 nT, or 0 dBuV=
/m<br>
=3D -70.5 dBpT.<br>
<br>
Well done, Stefan!<br>
<br>
Kind regards,<br>
Markus (DF6NM)<br>
<br>
<br>
From: Roger Lapthorn<br>
Sent: Saturday, June 26, 2010 12:52 PM<br>
To: <a href=3D"mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group@blackshe=
ep.org</a><br>
Subject: Re: LF: DK7FC&#39;s DFCW600 8.97kHz transmission NOW<br>
<br>
Stefan,<br>
<br>
I wonder how strong the signal would have been on a RX loop rather than th=
e<br>
E-field probe? This would be worth checking.<br>
<br>
73s<br>
Roger G3XBM<br>
<br>
<br>
On 26 June 2010 11:50, Roger Lapthorn &lt;<a href=3D"mailto:rogerlapthorn@=
gmail.com">rogerlapthorn@gmail.com</a>&gt; wrote:<br>
<br>
73 - the first message proper on the Dreamer&#39;s Band Stefan?<br>
<br>
Kind regards<br>
Roger G3XBM<br>
</blockquote></div><br><br clear=3D"all"><br>-- <br><a href=3D"http://g3xb=
m-qrp.blogspot.com/">http://g3xbm-qrp.blogspot.com/</a><br><a href=3D"http=
://www.g3xbm.co.uk">http://www.g3xbm.co.uk</a><br><a href=3D"http://www.yo=
utube.com/user/g3xbm">http://www.youtube.com/user/g3xbm</a><br>
G3XBM =A0 =A0GQRP 1678 =A0 =A0 =A0ISWL G11088<br>

--00504502cf20c2c2b20489f10c4b--