Summary from DK7FC 20101002 VLF TX tests at SQ5BPF QTH
wersja polska english version
The signal was received by SQ5BPF in Warsaw, Poland loc. KO02MD. Stefan DK7FC was transmitting on VLF 8970Hz, with a 200m antenna supported by a kite, this antenna was 1/165 wavelength (for comparison it is like transmiting on 80m with a 48cm antenna). The estimated ERP was 27mW (with abt. 300W TX power). Distance from SQ5BPF is 904km. The mode was supposed to be QRSS600 DFCW, but due to equipment failure it consisted of manual tuning only.
DK7FC's CoilDK7FC kite with the antenna

In order to monitor the transmission two grabbers were established. All times are in local time, substract 2 hours to get UTC.

Grabber 1 was using a PA0RDT miniwhip-like antenna, with a bandpass filter (2 lowpass, 2 highpass Sallen-key filters). The output was sampled using the internal sound card of a DELL Lattitude D610, received under Spectrum Lab v2.72b04 under wine.

Grabber 1, showing the whole transmission:

Grabber 1, showing the S/N ratio (one grid is 20dB):

You can see the whole screen from the grabber HERE

Grabber 2 was using a 40m longwire antenna, tuned to abt. 8kHz , with a bandpass filter (simple one stage LC filter, and 1 stage 20dB amplifier). The output was sampled using the internal sound card of a DELL Lattitude E4300, received under Spectrum Lab v2.75b12 under wine.

Grabber 2, showing the whole transmission:

Grabber 2, showing the S/N ratio (one grid is 20dB):

You can see the whole screen from the grabber HERE

For comparison this is the grab from experiments on 20100403 (you can see the whole screen HERE):

You can see that the signal is barely visible. So this time there is a big improvement (would get an "O" report)!

Stefan's letter to the rsgb_lf_group mailing list:

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 15C 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 

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 ;-)

Results from other VLF tests HERE Klubnl