Re: VLF: 5,2 km distance on 8,97 kHz with an earth antenna

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Good luck with the next tests Stefan. 

Yes I agree that a poor conductivity soil/rock should give the largest "loop in the ground" (and best range) and that low contact resistance at each earth point will allow you to maximise the current into the ground loop. 

I wonder if any electromagnetic theorists here would be able to estimate the radiated power of such an earth mode "antenna"? 

Such structures (on a larger scale) were used at 76Hz for the USA's Project Sanguine to communicate with their nuclear submarines at great depths. At 8.97kHz the electrode spacing could be 176 times shorter. Also, we are not trying to counter many dBs attenuation in seawater, nor span the entire globe.  Also, with slow QRSS we can wait for our signal to appear and use extremely narrow bandwidths.

So, what I'm wondering is what do the maths say might be possible regarding radiated signals from such structures?

73s
Roger G3XBM

2010/6/26 Stefan Schäfer <schaefer@hst.tu-darmstadt.de>

Tnx Roger,

Today i have prepared further 9 rods for each pole, so 20 rods for each pole in sum now. Tomorrow in the morning i will drive again on the hill and try to even reduce the losses. When DHO38 comes back after its break arround 7...8 UTC i will try to transmit a message to my grabber using about 50 watts. I have already an idea what to transmit ;-)

I have thought about the losses problem: First we say that it is important to have a low ground conductance so that we achieve a big loop in the ground. But next we say that we need a very low local earth resistance at the poles. There on the mountain the earth conductivity seems to be very low and THUS it is not easy for me to get a low losses at the poles. It is the same dependency! Thus i have to do more effort to come down with the losses but it is better than taking just one 20cm rod and achieve 100 Ohm since it would mean that the loop area is small as well! Preparing those small earth rods is no problem. Even if i would need 100 for each pole i would do it (not worth to mention, compared to the work to wind such a coil ;-) ).

Today in the morning the QRN was pretty low but in the afternoon it rained. I hope for good conds tmw. :-)

In further tests i plan to study the influence of rain and temperature and so. This can be done by using QRP (e.g. 1W TX power, supported by a solar cell and a battery) and my DFCW-6000 window or even the DFCW-60000 window that will cover about 7 weeks!
The 60000' window is running since about 2 weeks and is available here: http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html DFCW-60000 is not really suited for a QSO of course but it gives a good overview of the QRN dependency during the summer time. And it is suitable for transmitter tests if one can run a transmitter for some days or a week. Even slower, i have added a "Annual overview" window but it will take some months to have a real information there...

73 es gl,
Stefan/DK7FC


________________________________

Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von Roger Lapthorn
Gesendet: Fr 25.06.2010 09:44
An: rsgb_lf_group@blacksheep.org
Betreff: Re: VLF: 5,2 km distance on 8,97 kHz with an earth antenna

This is excellent Stefan.

In your case it is much more probable you are seeing true earth mode propagation not aided by utilities in the ground, although it is hard to avoid them. It will certainly be worth trying reception on a loop antenna with the loop orientated both (a) in alignment with the earth electrode loop and (b) flat on the ground. Also it is worth trying a lower frequency like 838Hz where I've been doing my recent tests.

In all, I am VERY excited about your tests and results. Thanks for sharing them here.

Last night I managed to get 5.25km (my best DX yet), but this was definitely aided by utilities. Tests at many other locations out as far as 6km to the west and north totally failed to produce even a faint trace on the Spectran screen using QRSS3 on 838Hz.  Information on my website as usual. See http://sites.google.com/site/g3xbmqrp/Home/earthmode .

73s and good luck

Roger G3XBM



2010/6/25 Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>


       Dear LF/VLF,

       Today i spent more than 8 hours in the forest on a hill 520m ASL, improving and experimenting with my VLF earth antenna. It was a fantastic and very successful day that gave a lot of fun and motivation. BTW, just spending time in this wonderful nature with all its beauty cannot be wasted time even if all the experiments would fail :-)))) That is what i thought many times this day. If you live in a city with much noise (on the band and audible) you may understand what i mean when i say that all you can hear there is the wind and some birds!

       Since there are a lot of photos and things to tell i set up a pdf document with my report that is available at http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF_5km_with_an_earth_antenna.pdf , for the VLF enthusiasts (Dreamers!) and those who want to become one! :-)

       Best  73, Stefan/DK7FC





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G3XBM    GQRP 1678      ISWL G11088

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