From:
Stefan Schäfer <[email protected]>
To:
[email protected]; Paul <[email protected]>;
Renato Romero <[email protected]>; Bernd Grupe
<[email protected]>
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 :-)
