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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