Testing on the 33km band
Where does one start?
Stefan - this is simply BRILLIANT experimental work. Thank you for your hard work and for sharing it with us here. I wish you and everyone else all the very best in pursuing this further. Clearly this is just the start.
Paul, Marcus etc - thanks for watching at the other end and making the screen shots.
Mal - your comments are noted, but I think there is little room for doubt that the signals received were from Stefan. It will be good to get a full and positive identification in a later test everyone would clearly agree. Everyone is now awaiting your big signal on this band from the UK.
And to think I get excited over a few hundred kilometres on 500kHz.
Wow!! This has been so exciting to follow.
73s
Roger G3XBM
2010/3/16 Stefan Schäfer <[email protected]>
Dear LF group, RXers and 9Dreamers and doubters,
Thank you for your assistance on that very successful experiment! It is a good day for the VLF ham operations and it won't be the last. YOU are a part of this success since i wouldn't have done all the effort to become QRV there if you all wouldn't have been so interested in the discussion about <9.
So, perhaps there will come up further TX stns, i hope so. With the results we can see what can be reached with a given ERP in a given distance. So, all the theoretical calculations become less speculative...
First, i confirm that i was QRV to the described time at 8,9700kHz.
I will detailed describe now what happend on this experiment.
Starting with buying a plastic spray paint and fixing the windings on the water barrel was the first work. Than applying the variometer and the primary coil.
The primary coil is inductive coupled to the secondary and isolate mounted on the bottom side of the water barrel. It has just 9 turns out of 4*0,4mm diameter isolated copper wire. The 9 turns was an estimation but later it is shown that it is optimal for getting the maximum output power at moderate voltages and currents.
On http://www.qrz.com/db/DK7FC i will show many photos i have taken on the hill. So there may come up some questions and some may be answered by the pictures ;-)
After building up the kite (the 8,1m^2 type due to a little unstable wind) and applying the whole equipment i started some resonating tests. The variometer part has a litte too much L so it is sensitive to adjust but never mind. It was easy to resonate and after transmitting a long carrier i noted that the heat sink of the PA remained absoultely cold. Then i increased the output voltage and got an average DC current (PA input at 13,8VDC by a SMPS driven by my fuel generator) of about 13A during the whole transmission time. The PA still remained cold but it was fused with 10A and i had a amperemeter of 20A full range, so i didn't further increase the power. The current came up to 18A and go down to 9A during the kite movement.
During the whole transmission, there were no HV problems! Just one time the wind turned and suddenly the antenna wire got disconnected with a 8,97kHz noisy 2cm long spark ;-) The DC current immediately decreased to < 1A so that case is no problem for the PA.
I was in telephone contact with Bernd/DF8ZR and started to transmit some undefined sequences. Later i built up the notebook and installed the LF sequencer and keyed the TX in QRSS30. Bernd copied it difficultly in a distance of 16km. He clearly catched a 2 minutes transmission to that time i transmitted it.
I forgot to take the 1 Ohm current shunt resistor and the probe to watch/measure the current with the oscilloscope but later i rembered that i have a "true rms" digital multimeter with a range up to 10 kHz and so i could easily measure the accurent antenna current. The average antenna current was about 480mA!
So, the voltage was abt 15kV rms. Since there were no HV problems there is the possibility to increase the ERP at least by 3dB.
Andrey: No, the coil does almost not sing. The sound of the PA transformer is louder (only a little, not too nerving) but all that is blown in the wind ;-)
Paul: My exact QTH is http://maps.google.de/maps?hl=de&ie=UTF8&ll=49.77647,8.699525&spn=0.001607,0.003428&t=h&z=18 (see the coordinates in the link). So: >Bearing of this signal was 117/297 deg. Frankfurt is on 114. This is pretty exact! Congrats to your RX antenna system, Paul, very fine!! So, what is the new WR? I do not have a program that calculates the distance accuratly out of the coordinates...
Later i got a mobile call from DF6NM who told me that the signal is visible on his grabber. To that time i tried an unsuccessful QRSS10 test with Bernd. Later i switched to QRSS120 to write "DK7FC/P" there but it took 2,5 hours just for these few letters. Finally i just transmitted "DKM" since during the "7" the antenna wire (copper+steel-litz) broke. You can clearly see the "M" at the DF6NM grabber, the last sent letter for this day. The broken wire was due to strong wind: The kite needs a braid that is elastic (110% length at maximum force) to withstand the wind blasts, so the ant wire needs to have some sag and this sag was not enough in that moment, so the whole force turned to the wire. No problem about the wire, i have enough for the next test...
To the earth resistance: R(coil)=300Ohm and P(PA (with abt 100% efficiency))=180W, so the earth resistance seems to be about 480 Ohm. Hmm, seems to be a little much but it includes all the other additional losses such as coil losses due to the H stray field near the earth... I will measure this more accurately the next time. BTW i measured the voltage waveform with a loosely capacitive coupled HV probe. The sinus form was OK but could be better. But the C coupling is a high pass and so the harmonics may be not so strong as displayed... Listening to the harmonics with my IC706 gave nothing, nice.
My first question (others surely will come up later): What is the achievable groundwave distance on the 33422m band? ;-) And what do you expect is possible at night? Maybe, if we now have 830km (?, not 840?) we could even get much more...
Maybe i have forgotten to answer some questions but this mail is already long enough. So, will go on tomorrow. Now uploading the pics...
73 es GL, GN, 9 dreaming...
Stefan/DK7FC
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G3XBM GQRP 1678 ISWL G11088
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