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Date: Thu, 13 Oct 2011 17:26:35 +0200
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: noise on VK and earth dipole tests
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Hi Dimitris,

Am 12.10.2011 23:47, schrieb Dimitrios Tsifakis:
>
> Was the 450 km reception done during the day or night?
It was in the evening. The mail and screenshot is in one of the 1000s of 
mails here in the reflector. Must have been about a year ago. RX station 
was F5WK.
>   At that
> distance I am guessing the RX station is not receiving anything from
> the earth, it will all be coming from above ground.
I think as long as it is not conduction (which is limited to some km) 
even my VLF transmission received in 46 km by Michael Oexner was ground 
wave, not through the ground. The idea is that the current flowing into 
the ground forms some kind of loop that is radiation some uW, coming out 
of the ground (hill) and beeing propagated as if it comes from a usual 
vertical antenna.


> By the way, why did you elevate the wire off the ground? I am just
> letting the (insulated) wire sit on the ground.
To get a better effective area and to prevent that someone stumbles over 
the wire ;-)
>   I think that this
> results in more energy transferred in the ground capacitively. Maybe I
> should try elevating the wire to see what difference that makes.
>    
But you want the current to completely flow into your far end electrode, 
not beeing capacitively coupled into the ground before, which would also 
reduce your effective area and thus the efficiency.
>    
>> Well, on VLF it is a pure earth antenna but on LF it must be a mixture of
>> that and a low short wire above ground.
>> I haven't done excessive experiments on LF, like finding the radiation
>> pattern and so. Maybe that would be interesting.
>>      
> With the limited experiments I have done, I think there is some
> directionality but it's hard to say if this is due to the geology of
> the area or the direction of the earth dipole.
>    
It must have to do with the different conductive and capacitive layers 
into the ground and is difficult to estimate i think. Of course the 
geometry of the hill, i my case, plays a role too. Soemhow it jeems to 
work though ;-)

>
> If it can't be done in VK, then it can't be done!
So it can be done in VK since it can be done :-)
>   I may need to travel
> a bit further out, but I am very very sure this is possible here. Now,
> where do I get 6.6 km of wire? :-)
>    
Use simple mains house wiring cable, i.e. 3x1.5mm^2 or what you have in 
VK. We are getting 50m (i.e. 150m) for about 7 EUR. You can start with a 
shorter length of course and see what comes out so far. I have started 
with 120m and reached 2 km distance with a bad earth and 6W RF power ;-) 
But that's near field. On 8970 Hz i can reach my grabber in 5 km 
distance at 35 dB S/N in DFCW-600 when i use 150 W TX power on the 600m 
spaced antenna.

That would be a great LF RX antenna as well! Really looking forward to 
your first results, if you actually want to start in the VK landscape on 
VLF. If you need a schematic for a nearly 100% efficiency PA, 300W at 
12VDC (car battery), see 
http://www.iup.uni-heidelberg.de/schaefer_vlf/12V_300W_VLF_PA.pdf :-)

> Anyway, I am having a good vibe about experimenting more with the
> earth dipoles, so the next steps will be more wire, more power and
> different configurations. I am feeling much more relaxed pumping more
> power in the ground because it has such a nice and predictable purely
> resistive impedance
That's true!! I don't use a coil on VLF too. The impedance almost equals 
your earth electrode resistance i think.

Can you give me a locator where you think you will start with first 
tests? A nearby sea sourrounded by dry desert or rocks would be fine. A 
stone hill or so...
The ground below the earth electrode must be BAD conducting even if it 
makes more effort to get a low earth electrode resistance.
>   - no fiddly and dangerous inductors are needed,
> just a good ol' impedance transformer.
>    
Yes and no HV, not even high currenty in the secondary path. And you can 
measure the antenna current with a good digital multimeter, see 
http://dl.dropbox.com/u/19882028/VLF/DSC03246.JPG which was a photo 
taken during a VLF test in the forest near Heidelberg ;-)


Vy 73, Stefan/DK7FC