Fascinating indeed Stefan. Keep up the good work!
73
Joe VO1NA
On Sat, 8 Oct 2016, DK7FC wrote:
Hi ULF,
This night i have completed the 4th stack of my large *ULF loading coil*.
An image:
*https://dl.dropboxusercontent.com/u/19882028/ULF/20161008_ULF_TX_coil.jpg*
The exciting question was, what is the new resonance frequency together with
my antenna. In the lab i put an equivalent C in parallel and found the
resonance peak at *3.67 kHz*. So the L seems to be *3.8 H* now. This is still
not enough. The l/d of the coil dimension becomes larger now, so i need more
and more wire to reach the final resonance frequency of 2.97 kHz at about 500
pF.
I will do a next test on the actual resonance frequency in some days, when
the WX permits. I will also check where the resonance can be found when
switching the small coil in series that i use for 6.47 kHz now. It could be
quite close to 2.97 kHz then! So maybe this allows a next QRO step on 2.97
kHz: 100 mA antenna current must be reached for the planned experiment in 65
km distance.
BTW the 4 stack coil is wound out of almost 4 kg of enameled Cu wire with 0.4
mm diameter. The layers are isolated by Kapton tape. My assumption is that it
will hold 20 kV now.
Ah and the *DC resistance is 445 Ohm* now. When connecting 275 V AC / 50 Hz,
i can measure 269 mA. So the actual inductance is *2.93 H* (beeing farer away
from the self resonance frequency)
I can tell you it's quite fascinating to operate down on these low
frequencies :-) To be continued...
73, Stefan/DK7FC
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