Hey Wolf, LF,
A VLF grabber would be very fine! If you can arrange that, it would perhaps be
a motivation for the dreamers ;-)
A cooling of the coil will not be necessary unless i exceed the 1kW level, it
was only jokingly;-) (There will ever be wind since i need it for the kie ;-) ).
Wolf, thank you for bringing up the idea with the water butt! Since i was in
the near of a building center i looked for those and really found one that was
ideal and cost just 14,5 euro, the limit ;-)
Yes, i have mounted a DC motor vertically on my stable LF coil and drilled a
hole in the center of the big water butt. Then i attached it on the axis of the
DC motor. Appling the rated current when standing still it was possible to
rotate it with an individual speed, just as needed. So i got the coil ready in
just about 7 hours ;-)
The new characteristics are:
L=486mH (still some mH less but probably enough. A variometer part will be
adapted, if necessary. This will be seen in the second test on the hill.)
R(DC)=258 Ohm
Q=80
It has about 1100 turns. Average diameter is about 0,55m, hight about 0,5m. So,
the active wire area is abt 1m^2 and with the wanted current of 0,65A the
losses will be abt 100W, no problem ;-)
Wires are attached by a double sides bonding tape.
Before i bring it out of the house i want to attach some shielding spray paint
so that the wires are bonded to each other. Thermal expansion would destruct
the precise wound wires. And the paint will make the windings more resistant to
shocks/stress.
So, if we assume earth losses of 200 Ohm and coil losses of say 280 Ohm, we
will get the full 650mA antenna current (needed for 20kV rms at 9kHz and 580pF)
with a TX power of 200W. This will be reached in the next step! :-)
Bernd, DF8ZR has done improvements on his VLF antenna and can now also see the
alpha stations with abt 15dB S/N, so his RX wasn't really suitable on the last
test since he saw nothing of the alphas before! So, the next test might show a
good reception, especially when we think about what Markus/DF6NM has reached in
the last days. Congrats, Markus!!
Wolf, are you ready for the 220km distance? ;-)
Stefan/DK7FC
PS: What do you think about using parallel wires as the antenna wire, just like
wir man ladder line? In the HV power transmission cables one can see this
method to increase the pd inception level. This might be an idea to increase
the maximum voltage!
________________________________
Von: [email protected] im Auftrag von Wolfgang Büscher
Gesendet: Sa 06.03.2010 12:31
An: [email protected]
Betreff: Re: AW: AW: AW: LF: Re: 9kHz noise level
Hello Stefan,
Well, if really necessary one could cool the barrel from inside - not by
filling it with water from the pipe of course; and carrying such an
amount of distilled water to a portable site would be overkill. Better
use a fan which keeps the air inside the barrel (or your tube)
"rotating" while blowing cold air into it (at the bottom) while leaving
the warm air escape at the top. Maybe the furnace effect is sufficient -
experimentation will show.
Good luck winding the coil - hope you have a lathe or somebody else to
help you with that. Reminds me of my tesla coil experiments, but they
are much smaller than your coil.
With some luck, I can get the internet link to the club station (DF0WD /
DK4U) running again soon - if successful, I can put up a temporary
grabber there, or resume my VLF streaming activities (by help of Paul's
VLF streaming server). The question is if the MP3 or Ogg Vorbis
compression will leave the weak signals intact; at the time we started
those activities it was intented for VLF natural radio but not for
hunting extremely weak signals.
Cheers,
Wolf
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