Re: VLF: 2km on 8,97 kHz using 6W TX power and a 120m earth antenna

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Stefan, 

A few observations on your tests using the earth electrode "antenna" today:

1. In my experience, most of the signal transmission is by induction, so I think it would be worth trying to receive the signal with a loop antenna when the received signal may be much stronger than on the E-field probe. In my case I use a 30turn, 80cm square, loop which can be rotated to minimise 50Hz interference.
   
2. On my 10m and 20m baseline earth electrodes I was measuring resistance of between 40-60 ohms between 1-9kHz, so your figure seems very high. This may be as a result of the soil and rock type in your area but this is worth checking. If my theory of the "loop in the ground" is correct then a poor conductivity soil would result in a larger effective loop area within the ground.
   
3. Did you try matching the PA to this high impedance through a transformer? I think not in this test, so better results may well be possible.
4. Regarding Mal's comment about "you need a 100m high antenna", well you know this works, but the point of this experiment is to see how effective, or not, an electrode "antenna" is. The results are valuable whether good or not.
   

Here, I have completed a further "by ear" range test using my TDA2003 4W PA into a 20m base electrode pair "antenna" walking around the village in many different directions using the 80cm loop RX at around 1.5kHz. I improved the 50Hz rejection this week by adding another Sallen-Key HPF. When walking over metal pipework in the roads the signal is strong up to at least 0.25km in almost any direction and limited by 50Hz noise. When walking across fields well away from pipework the loop orientation exactly lines up with the base electrode "loop in the ground" at distances up to 0.5km.  I have not managed to hear the signal at any further distance in any direction. My grandson is back staying with us all next week, so very limited chance for more experiments until about June 14th. I have a long list of things to try still!

73s
Roger G3XBM

2010/6/4 Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>

Dear VLF,

As mentioned in the subject i have done a test on 8,97 kHz today in the morning, where the natural QRN has it's lowest level during the day.

I used a 120m long wire antenna that was placed just on the ground. Since the earth losses were very high i have jut got 6W TX power out of my 300W PA.

See my detailed report with many pictures and the results on: http://www.iup.uni-heidelberg.de/schaefer_vlf/Earth_antenna_120m_transmission_2km_DK7FC.pdf


Today, there were transmissions at least by DJ2LF, DF6NM, DK7FC on the dreamers band. It seems we need something like a band plan soon, hi :-)

Best 73 and good luck, Dreamers!

73, Stefan/DK7FC

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