I got some feedback that the link to the video wasn't working because
Dropbox is blocking the link, they say it causes to much traffic. Its
overdue to find an alternative!
Here's the link directly from the uni server now:
http://www.iup.uni-heidelberg.de/schaefer_vlf/20160702_222257.mp4
73, Stefan
Am 27.10.2016 12:28, schrieb DK7FC:
Hi Luis,
Am 27.10.2016 11:40, schrieb VIGILANT Luis Fernández:
Amazing work Stefan !! :-O
I bet you have constructed
some kind of support (like a lathe) which lets you rotate the
pipe easily and wound the coils . Right ?
Right! See:
https://dl.dropboxusercontent.com/u/19882028/ULF/20160702_222257.mp4
It's quite comfortable but still a lot of work.
This is getting really heavy
and the quality of coils looks very nice and repeteable ...... at least
five times ! ;-)
5 kg of copper wire so far. Still quite managable.
Dumb question: Why do you
get different inductance values when resonating it with antenna
equivalent capacitor and when measuring current at 273V AC / 50Hz ??
Shouldn't be inductance a
constant value ? ...... or I'm missing something obvious :(
It's due to the inner-winding capacity which is higher than on a single
layer coil. At the self-resonance frequency you need no external C to
get this resonance, of course. Then add just 10 pF external C. The new
resonance frequency will be almost the same. If you calculate L from
that frequency and C, it will be a gigantic high value, several GH :-)
Assume the internal C is 100 pF. And L is 4 H. Then f res will be about
7.9577 kHz. With 10 pF external it will be 7.5874 kHz. If you ignore
the internal C and say "I'm getting 7.5874 kHz with just 10 pF
connected to the L" you would calculate L = 44 H!
So you need to switch a much larger C in parallel to L so that the
internal C becomes irrelevant. Maybe 1 uF, then you will get 79.6 Hz at
4H. When calculating L with 1.000001 uF (1uF + 100 pF) and 79.6 Hz you
will get 3.997 H, which is quite correct!
It doesn't need to be a resonated circuit of course. You can also apply
a constant voltage and simply measure the current. But you need to know
the DC resistance then. Then Z = U/I = R^2 + XL^2 and L = XL / 314 (at
50 Hz).
Good luck with the 6th
floor. Seems that there is no room for a 7th, so that's why you
mentioned the variometer
I will first build the variometer now on a 16cm diameter and 6cm high
piece of tube. Will see what the tuning range is. You know, actually
i'm not a friend of calculations if i can do an experiment instead :-)
73, Stefan
Hi ULF,
It's just a few weeks ago, now the 5th stack is wound on the
coil: https://dl.dropboxusercontent.com/u/19882028/ULF/20161026_185804.jpg
The DC resistance rose from 445 Ohm to 572 Ohm.
The measured resonance frequency (using the antenna equivalent C in the
shack) dropped from 3.667 kHz down to 3.208 kHz. That should be
about 4.92 H.
Measured at 273V AC / 50 Hz, i'm getting 197 mA, so the actual
inductance is 4.0 H.
A 6th stack and a variometer part is needed!
73, Stefan
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