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Re: VLF: Re: DK7FC's 7th VLF kite experiment

To: [email protected], Paul <[email protected]>, Bernd Grupe <[email protected]>, [email protected]
Subject: Re: VLF: Re: DK7FC's 7th VLF kite experiment
From: Stefan Schäfer <[email protected]>
Date: Sun, 03 Oct 2010 01:53:14 +0200
In-reply-to: <[email protected]>
References: <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]>
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Dear VLF,
This was very nice to read. So many messages and so many positive receptions. I am really impressed!

Many thanks to you all who have been active on this day, watching on 8,97 kHz,  the Dreamers Band :-)

We have a new world record of the maximum distanced reception on VLF (by amateurs): SQ5BPF at a distance of 904 km with excellent S/N. Congratulations!! See attached picture.

Thanks to Markus/DF6NM for QSP to the reflector. Sorry to Wolf/DL4YHF that i was not QRV on 2m CW but there were problems to that time (see below). Thanks to SQ5BPF for the positive SMS ;-) Thanks to the US and canadian stations who tried to receive the signal. It becomes more and more probably since the S/N values are impressive here in EU.

Congratulations to all successful receiving stations, especially the new ones (on 8970 Hz) which are as far as i can see: Daniele Tincani, SQ5BPF, DD7PC, DF0WD, F1AFJ (683 km since my locator is/was JN49IS), F5WK (very impressive S/N 25 dB at 460km distance!), DL3ZID(463 km) :-)

Those S/Ns we have seen in this test seems to make even much more possible in future experiments. And the QRN will even go down in the coming months i hope.

My todays report:

It was raining in the early morning and i asked myselfe if it makes sense at all to go out of the bed. But i did and as i finished packing all the stuff in the car the rain stopped :-) Arriving on the hill there was everything wet and my copper ground plate was hidden at some meters into some buddles. So the earth losses were reasonably low!
After building up the wind was even strong enough and almost during the whole experiment the wind was strong and stable. The kite was in an angle of 60 deg and above. First i used the 3.6m^2 kite, later the wind was a little weaker and i changed to the 8.1m^2 kite. The antenna length was 200 m (about, maybe 220 m).
The first time i became QRV on 8970 Hz with the 200 m vertical after finding the correct tap on the coil which reduces the DC resistance by 100 Ohm.
Also the first time i measured the PA power by a true rms digital multimeter which has a mains adapter and can measure (U, I, P, cos phi). The average power (resistive power in W, not VA) is, to my surprise, just arround 300 W. Anyway i reached an antenna current of more than 1 A. The amperemeter was hanging on the right catch sometimes, just as it has to be ;-) So this goal is reached! :-) I have to change the measuring range now ;-)
Feeding 1 A in this antenna means just about 16 kV on the antenna and an ERP of 27 mW. The overall losses are now estimated to be 380 Ohm (180 for the coil). The antenna efficiency is now 0,0037 % :-). So, the 50 mW ERP level was not reached. I think this is due to the changed ratio of the winding turn numbers of the coil, so  i have to reduce the primary turns in the same ratio (70%)...
300 W means that even 3 dB more should be possible with this generator but this will probably be the maximum ERP i can achieve, at least on a 200 m antenna ;-)
First there were some problems with the FET drivers (2x IR2110 for the H bridge) but after making a connection between ground/earth/soil and the heat sink it was no problem at all for the rest of the time. BTW: Still the first FETs in the PA(s)! During finding the problem i used my small class D PA with the 12V input and achieved 600 mA antenna current.
Actually i wanted to transmit "CU" on 8970 Hz but later i saw that the DFCW switch didn't work. So it was just a 40 minute carrier instead of a C, never mind ;-) Later i changed manually the DFCW step during telephoing to Markus/DF6NM ;-)
Suddenly the fuel of the generator was gone and i made a stupid mistake. It is a two-stike engine and needs some oil into the fuel, 2%. But instead putting the oil into the fuel i put it into the tank and later put the fuel in the tank too. This caused that the oil was in the engine and carburettor (100% not 2%) :-( Thus it was not possible to get the generator running again. More than 100x i tried to start it but no chance. During the tests to get it running again the kite was at a very high angle, about 70...80 deg and it was very stable for hours! No wind problems at all this time. Thus i started the small PA again and got the power from the car generator. The volatge was lower as it seems. This seems to be the reason for the... aah, i just got idea that it was the temperature rise of the car engine that heated the VFO and thus my last carrier dropped continously in frequency. The VFO was placed on the car, you know ;-)...
OK, after a longer carrier i stopped since there was no chance to get the generator running and so i finished my 7th experiment at 15°C and optimal wind and a nice saturday afternoon at low QRN :-/ But anyway it was a great success, isn't it? :-)
Sadly, there was no chance to transmit on 6470 Hz since the H bridge PA has to be used for this (ferrite core of small PA is already in saturation at 6470 Hz). Also a longer carrier would have been good on 8970 Hz during the time of the Florida's QRN minimum (sri Paul), but the 40 min carrier should be fine for long time integration tests. Maybe a surprise will come up by Paul? :-)
The CW tests were not done since the signal levels have been to weak at DF8ZR and most probably even on my grabber. But i have recorded an audio file and will try to bury the CW signal out of the noise in 40 km distance...

If the QRN is at least as low as today and i can manage to add a last 3 dB power it should be possible to cross the pond i can imagine. Furthermore i will try to arrange a 300 m vertical on the next experiment and will transmit on (arround) 5170 Hz, the 58 km band! ;-) Coming back with 300 m on 8970 Hz means again 3 dB more. It seems to have no end ;-) BTW: i have heared about special licences for kites up to 1500m above GND! ;-)
Another advantage in the next test will be a GPS tracked VFO signal, the GPS module is already ordered...

OK that's i have to report so far ;-)

Some photos of the experiment will appear on

Again many thanks for all reports and screenshots and i hope you will take part of the next experiment, that will be in some weeks (maybe just 2 or 3). Maybe other experimenters will come up soon? Would be nice!

73, Stefan/DK7FC

PS: Thanks to Guido/DF9PW for the visit ;-)


Am 02.10.2010 12:54, schrieb Jacek Lipkowski:
I've set up a 2 temporary grabbers (slow connection so don't abuse it)

DK7FC is clearly visible

The QTH here is Warsaw/Poland KO02MD

VY 73


Attachment: VLF_WR_SQ5BPF_904km.jpg
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