Re: VLF: DK7FC's 6th VLF kite experiment

[Dave Pick <davepick@btinternet.com>]

Well done Stefan!

 

Nothing seen in Birmingham I'm afraid but, as you say, the noise level seemed quite high.

Your report reminded me of my first trips to North Scotland with the kite antenna on 136kHz.

Watch out for static charged rain!....

73

Dave G3YXM

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From: Stefan Schäfer <schaefer@iup.uni-heidelberg.de>
To: rsgb_lf_group@blacksheep.org; Paul <paul@abelian.netcom.co.uk>; Renato Romero <contact@vlf.it>; Bernd Grupe <bernd.grupe@t-online.de>
Sent: Monday, 2 August, 2010 12:01:32
Subject: Re: VLF: DK7FC's 6th VLF kite experiment

Dear LF/VLF group,

Many thanks to all the people who tried to catch may signal in the yesterdays test! Thanks for taking the time to watch the QRG on a sunny sunday! The RX side is an important factor in such a experiment because it motivates the TX side when there is no QSO but just a reception. It makes me glad that there is such an interest in those tests.
Special thanks to Paul Nicholson who did the effort to re-arrange his antenna and software and the website with a nice overview.
Also special thanks to Markus/DF6NM for the telephone support about the activity on the reflector, the lightning situation and the QRN situation. This is an important feedback as well and much more interesting than just having a mobile internet stick.

Congratulations to all the successful receiving stations! It was a test in the middle of the summer time with heavy QRN. The QRN was on its daily maximum as i was able to transmit at a high kite angle. The QRN was even high compared to the last days during that time (still comparable in my DFCW-6000/8,97 window on the grabber1). So, there is MUCH potential to get a much better S/N in the winther period and at better wind situations. Thus, i am very hopefully that e.g. Jim and Paul will catch that signal! This makes the following experiment an optimistic challenge! I am even sure that it will be possible to go down in the DFCW-mode, maybe to DFCW-60. This makes it possible to try a cross band QSO (!) like 137kHz/6,47 kHz (or 8,97 first). Here i could use a small portable active antenna for 137 that will not be too much swayed be the TX antenna...

As far as i can see there was a positive reception at least by the following stations:
DF8ZR (QRSS-60 mode, 16km)
DK7FC (grabber in DFCW-240 mode, 40km)
DD7PC (congrats, first time! 53km)
DF6NM (insecure, fragments, 180km)
DL4YHF(impressive S/N!, 264km) Best DX reception of the lowest signal, transmitted by an amateur so far (far field)

Paul Nicholson told me that he has recorded the siganl and will try to work the trace out. Let's be excited about his proffessional and nice to read report!


Now, i want to give a detailed report of the things that happened on the TX side:

I arrived at about 9:40 UTC. It was no problem to arrange the equipment and nothing was forgotten. Just before, the rain stopped but the wind was a little to weak.
I used the 8,1m^2 kite but it took some hours until the wind was enough, sadly. First, the wind increased just for some minutes. In that time i saw that the wire was to long and was sagging to much.

After cutting some meters i could start the generator and PA and turned the VFO wheel down until i saw a peak on the amperemeter. It was on 5,7 kHz but it was due to a very low kite angle. Later, as the wind increased i could do more useful resonating tests. I found that i can resonate between about 6,4 kHz to 6,6 kHz. Maybe this is due to the fact that the wire has to be slighty longer than 200m since the kite braid is elastic and will be 20m (10%) longer at strong wind.
After watching the 6,5 kHz sector in the last weeks i found that it is best to transmit not on n*50 Hz or n*16,6667 Hz (frequency of the german trains grid). Thus i decided to go about into the center, to 6470,00 Hz, within the 46 km band! :-)
First it was not possible to transmit a real "message" since the wind was OFF sometimes :-(. My plan was to transmit "CU" in DFCW-600.

Than, an accident happened: Suddenly the was was off and i wasn't fast enough to bring the kite down on the road. So the 200 € kite dropped in a 15m high tree! I felt like a child that lost his parents on the airport! I was not strong enough to pull it out there with its braid. I saw no other way to try it with the car, even when the kite gets damaged with this attempt. So i fastened the braid on the car and drove some 10m until there was a heavy pull on it. The braid stopped in a beginning corner of a corn field and as i lifted it above the corn it sounded like a lash/whip. But suddenly the kite came out of the tree and before it dropped on the bottom it was caught by the wind and rised into the sky, hanging on my car :-) I drove back the the TX coil with the kite on the car...

After taking too much sun and after this stress i was powerless and not motivated to improve the earth losses and so on but it was my absolute goal to produce some nice signals for the RX stations, at least a limple carrier! So i set up the whole arrangement and now the wind was stable, lifting the kite continously above 45 deg, sometimes 70 deg. In proper wind conditions, it is lifted to 70...80 deg.
The antenna current was about 750mA and after connecting the copper rod i hammered into the soil in the 5th experiment it rised to 800mA. Then i reduced the primary winding number from 70 to 60. Then, the current was up to 920 mA, the highest current so far. Just before 16 UTC the fuel of the generator was empty and my fuel as well ;-) That was the end of the 6th experiment.

So, my overall losses are about 600 Ohm now. The ERP was about 11mW and the voltage just about 20 kV rms. I am sure to be able to decrease the earth losses to 200 Ohm and the coil losses will be reduced to 200 Ohm as well since i can reduce the L to come back to 8,97 kHz.

Now i know the C of the wire and can make a reasonable tap on the coil, at arround 275 mH! So, in the 7th experiment i can transmit on 6,47 kHz as well as on 8,97 kHz. I just have to change the coil connection and the VFO frequency and that can be done in < 2 minutes.

I will spend some experiments on this 200m antenna now before going to 300m. And i want to test it on 137 kHz ;-) With a 300m antenna, i will explore the 58km band in future tests! Also, just for fun,  i want to transmit on 7355 Hz. This frequency is a message in it selfe for amateurs ;-)

So, all in all it was a hard experiment with many difficulties and the QRN situation could have been at least 15 dB better but it was an important test to find the tap for the L to come back on the Dreamers Band (33km) with a 200m vertical. Also we have done some new record receptions and can be very hopefully that this can be much improved in the next test, if there is proper wind and less QRN that can be assumed when going to the autumn :-)

Again thanks to all the group and hope cuagn in the next test! :-)

Best 73, Stefan/DK7FC

PS: Some photos and screenshots will be displayed on my QRZ.com page in some days.

PPS: Hopefully there will come up further stations on the dreamers band within this year :-)