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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