Selfrunning cold electricity circuit from Dr.Stiffler

[gotoluc]

(This is the point why birds can sit on high voltage wires - and humans cannot)
(The capacity of a bird to ground is very low - evolutionary ;-))darwin?)

rgds.

Man on a wire

http://www.youtube.com/watch?v=HcalasGr_uk

[edork]

Hi fritz!

Where White LED, Green LED lower voltage drop?

When you light 150 White LED like Stifler I shake your hand.

[fritz]

The self resonant frequency of an AM ferrite antenna is around 10MHz.

Hi Fritz,  have you measured that to be around 10MHz or you judged?  If you only judged, I would say you are probably correct if you remove the ferrite rod from the coil and  refer to the self-resonant frequency of the now air core coil, right?.   

Because the high permeability of the ferrite core would still dominate the inductance of the coil at 10MHz (even though the permeability certainly gets reduced with increasing frequency) so the presence of the core would not let such a high self resonant frequency.  Do you agree?
My understanding is an AM ferrite antenna coil has approximatly  600-700uH of self inductance around 0.5-1MHz. Suppose it still has about 70uH inductance left at 10MHz, right?  This 70uH needs  about 1.5pF (distributed and parasitic capacitance) to resonate at 10MHz, right?  And the AM coil on the ferrite rod surely has higher than 1.5pF distributed cap due to the many turns of wire, this surely has to lower the self resonance frequency of the ferrite antenna well below 10MHz.

I measured (my) coil with LCR meter at 1kHz -  has about 400uH - but it
has less winding than the "original".

To measure the self resonance frequency - I operated the primary coil (9 turns)
with my siggen from 1-20MHz.
I connected the tip of my osc probe to one end of the AM coil. (....)
There are regularly resonances with 120% nominal amplitude every 1.5Mhz (est.)
and a 300% resonance overshoot around 10MHz.

I agree with your estimates for the values at 10 Mhz - to measure this exactly - I
have to repair my other LC meter which is capable of measuring even with 10MHz
frequency ...

By moving the ferrite coil in and out at resonance frequency - shows a variation of
amplitude at the AM coil with a factor of lets say 5. On doing that - you can additional
watch the capacitiv coupling between both coils:
Very nice:
Hold one end of the AM coil (yes this side gets grounded by your finger than) - and move
the ferrite core in and out. You see precisely that the dominant coupling changes
at some point from capacitiv (ferrite out) to inductive - ferrite enters part where both
coils are on top of each other. Nice phase change, looks very good.

rgds.

[fritz]

(This is the point why birds can sit on high voltage wires - and humans cannot)
(The capacity of a bird to ground is very low - evolutionary ;-))darwin?)

rgds.

Man on a wire

http://www.youtube.com/watch?v=HcalasGr_uk

This man is wearing feather-alike clothes, the wire is not that with
the real high voltage (look at the insulators).
I wont do that naked ;-)))
rgds.

[gyulasun]

I measured (my) coil with LCR meter at 1kHz -  has about 400uH - but it
has less winding than the "original".

To measure the self resonance frequency - I operated the primary coil (9 turns)
with my siggen from 1-20MHz.
I connected the tip of my osc probe to one end of the AM coil. (....)
There are regularly resonances with 120% nominal amplitude every 1.5Mhz (est.)
and a 300% resonance overshoot around 10MHz.

I agree with your estimates for the values at 10 Mhz - to measure this exactly - I
have to repair my other LC meter which is capable of measuring even with 10MHz
frequency ...

Hi Fritz,  ok, thanks for your answer, I understand and agree most but please consider the oscilloscope probe has got a 13-15pF loading capacitance in parallel with its 10MegaOhm input resistance and that self capacitance significantly detunes the ferrite rod coil, right?  The best way to measure the self  resonance frequency would be to use a Grid Dip Meter (GDO for short) you surely know this calibrated LC oscillator that shows energy transfer to a passive tank circuit when it is near or at the resonant frequency of the passive tank.

Thanks, Gyula