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Registered Member #4187
Joined: Fri Nov 04 2011, 08:08PM
Location: Spain
Posts: 43
Hi,
I checked with scope and signal generator the tuning of my secondary today, I got some results that don´t undertand
1) with just the coil (no topload) I get resonance peak at 527kHz, theoric is 528,3 so OK. 2) with top load I get two peaks, one lower at 320kHz and another with higher amplitude at 384kHz. Theoric is from 300 to 321kHz, depending on toroid formule used.
Actually, the 320 and 384kHz peaks are really three peaks each (6 in total), but very closely spaced (about 1kHz between them). I needed to zoom in to detect this effect.
Measurement was done as suggested in some paper that I found, with signal generator(+) to coil and scope probe floating 1m from top of the coil. Coil was on the floor and >2m to walls.
That second 384kHz peak don´t seem to be predicted by theory, any suggestion?
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
the Fres is 527khz and the others are harmonics. the fundamental and harmonics are created by the capacitance and the inductance in each winding. if add a torid or get spark it will add capacitance to your equasion.
I use a pules generator to check my coils and tune for the highest peak by pulse width or frequency. a sign wave generator will work to. I generly don't care about the harmoncs just the one that gets me the highest voltage transfemation
Registered Member #4187
Joined: Fri Nov 04 2011, 08:08PM
Location: Spain
Posts: 43
Thanks for the feedback but sorry, I don´t understand you.
With the toroid the highest voltage seems to be with 384kHz, but this resonant frequency just doesn´t correspond with L and C secondary plus Ct (toroid value).
I know L & C values are correct, as resonance without toroid is correctly predicted & measured.
The doubt is with Ct, with this toroid, I have a first resonance at 320kHz (that seems to be in agreement with some toroid formulae out there) and a second, higher in amplitude, 384kHz resonance that supposedly would imply a lower value for Ct.
From 384 to 320 there is a x1,2 factor, i don´t know if this can mean something...
Registered Member #4187
Joined: Fri Nov 04 2011, 08:08PM
Location: Spain
Posts: 43
Thanks for the interest, I checked the link but I didn´t find any relation to my case as the second peak is quite lower freq.(384k) than the expected second resonance (640kHz for half-wave),
So if it is not a resonant mode, it may be in some way related to the toroid or stray capacitance?¿
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
One fundamental resonance is due to resonance between the effective secondary inductance and the combined effective capacitance of the secondary plus topload. This is the resonant frequency normally used by coilers.
Another resonance is due to quater-wavelength 'standing wave' of the secondary and topload acting as a transmission line with capacitive load. The coil acts as a 'slow-wave' device and has multiple resonances.
A coil with low H/D behaves mainly as lumped inductance and capacitance, with larger H/D the quarter-wave effects become more pronounced, I believe.
I remember reading that N.Tesla was quite excited when he found that by suitable choice of winding and loading he could get the two resonances to be at the same frequency when base-driving the coil in the so called 'Magnifier' arrangement, which gave extra high voltage. Tesla tried to avoid the arcs and sparks that we crave to enable wireless transmission of power, requiring as high a voltage as possible. For us the desired arcs and sparks load the tertiary coil such that I have not personally seen this phenomenon.
When a resonant primary is loosely coupled to a resonant secondary then the 'frequency splitting' discussed in the reference above occurs.
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Secondary, two resonance peaks
