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Date: Mon, 24 May 2010 17:48:47 +0200
Message-ID: <38A51B74B884D74083D7950AD0DD85E82A1C00@File-Server-HST.hst.e-technik.tu-darmstadt.de>
Thread-Topic: 8.97kHz - Near field and radiated signals?
Thread-Index: Acr7Ks63IqHPF31VQVOdfGrs/fK4fAAKSYUh
References: <AANLkTinG-0mJJ3CDqFwxeLXfOJXFFfs42gjLYz8yX3rW@mail.gmail.com>
From: =?iso-8859-1?Q?Stefan_Sch=E4fer?= <schaefer@hst.tu-darmstadt.de>
To: <rsgb_lf_group@blacksheep.org>
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Subject: LF: AW: 8.97kHz - Near field and radiated signals?
Sender: owner-rsgb_lf_group@blacksheep.org
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Reply-To: rsgb_lf_group@blacksheep.org


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Hello Roger,

For your ground electrodes, ground electrodes may be the best "antenna" in=
 some 10...10m. I'm not sure how to calculate field strengths but i just=
 know about the 1/d^3 dependency, so twice the distance means 8 times the=
 power for the same signal reception, in the near field. But it is the que=
stion what are the electrodes since there is ever a coupling to the mains=
 earth and all the metallic stuff in regions where people are living so th=
is dependency might not be valid in your tests. As mentioned here, you cou=
ld benefit from these conductors...

But if you want to reach more distance with an antenna of the same size (e=
.g. of your garden)and the same power, you could try such a TV transformer=
. Take a wire, as long as possible and as high as possible, and apply some=
 kV on it by this transformer. It can even be resonated by adjusting the=
 air gap between the both ferrite parts. That results in a maximum output=
 voltage and thus "ERP". At least this would be a good alternative to your=
 ground electrode tests. You could easily compare the reachable distances.=
 Here i would use a E field antenna for reception in the near field.

How far is your next receiving amateur radio station away? And have you tr=
ied to do such tests outside the village/city, just like Jim does it with=
 his loop antenna? This could allow you to increase the distance of your=
 reception. Here, space is not limited and you could try 2x10m, 2x50m, 2x1=
00m and so on and tell us the difference in the feed point impedance at va=
rious frequencies and your ODX :-) Maybe i will also do some ground electr=
ode tests in summer but i am still not sure. The complete receiver of Jim=
 is a really good idea to check the QRM situation at a given QTH. Probably=
 i will also buit his loop design for such tests... Would be interesing wh=
at is the maximum distance for a CW reception of my transmitted signal (wi=
th the kite antenna and 6mW ERP) ;-)=20

I will also do some near field tests in this week, to compare the performa=
nce of my 2 grabbers. This will be done here: http://www.google.de/maps?f=
=3Dq&source=3Ds_q&hl=3Dde&geocode=3D&q=3Dheiligenberg+heidelberg&sll=3D47.=
820666,9.312449&sspn=3D0.106733,0.219383&g=3Dheiligenberg&ie=3DUTF8&hq=3D&=
hnear=3DHeiligenberg&ll=3D49.419391,8.704101&spn=3D0.001616,0.003428&t=3Dh=
&z=3D18 in about 1,8km distance to my grabbers. Power will also be below=
 100W and the antenna wire will be mounted on a tower in abt 15m height.=
 I will transmit with this TV transformer on a 40m wire.=20

Roger, what size is your garden? What is the maximum wire length that you=
 can apply and in which height? What is your goal (best DX, a reals QSO wi=
th the next equipped station or just do some funny tests?)

So, wish you fun and success with your experiments!

73, Stefan/DK7FC

PS: What is your locator / QTH?

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