Re: secondary frequency problem (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 19 Sep 2007 19:41:04 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: secondary frequency problem (fwd)

Hi Chris,

Wow, certainly a different coil than I had envisioned!  80 turns of 1/4" 
wire with an 8" x 38" geometry is pretty cool and certainly the Q is 
going to be high (higher than a typical coil).

Regarding the 800kHz frequency: That indicates a lower 3rd harmonic of a 
2.4MHz fundamental with a 2nd harmonic at 1.2MHz. The fundamental we 
typically look at as a multiple of the fundamental (f) where the first 
harmonic = 2 x f and it's amplitude is 1/2 of the fundamental. The 3rd 
harmonic is 3 x f and it's amplitude is 1/3 the fundamental (and so on). 
For lower harmonics, just divide with the same understanding and you 
will find 800kHz is a 3rd lower harmonic.

I notice there is no ground plane inserted into Javatc (which "must" be 
inserted for any type of accuracy). This is important. Also, any objects 
around the coil will further lower the frequency (walls and ceiling 
included). I like to test coils out in the middle of the yard where I 
can remove as much external capacitance from affecting the measurement. 
I also throw down a metal ground plane below the coil which I use as the 
common signal ground (and I use it's dimensions as well for the ground 
plane). Also, the bottom of the secondary is stated as 0. You should set 
the actual bottom height value and then add 38" to that value for the 
top height.

Considering your 800kHz measurement and what you stated as a harmonic of 
1.2MHz, I expect you are certainly in the 2.4Mhz range for the actual 
fundamental frequency, but of course you can't measure that due to 
equipment limitations. I run into those same limitations myself all the 
time. One of my most frustrating times are frequency measurements 
because I usually like to check the harmonics as well and often I can't 
get past the 3rd harmonic.

Regarding AC resistance values from Javatc (and of course it's 
associated Q value), there were hundreds of real world measurements in 
which to compare. But Q measurements are difficult even for the most 
experienced. Here's a quick chart of how Javatc held up against all 
those measurements.
http://www.future-technologies.co.uk/temp/javatc.pdf

Note that above h/d of 3, Javatc did very well for such a difficult 
prediction, but below 3 the variation grew, yet still was in the 
vicinity. These however are normal coil geometry's and wire size. Your 
coil has a huge wire size for the coil geometry, so no telling since 
it's so outside the norm. One thing I can say is true, don't rely on DC 
resistances for Q. At RF, there "IS" an effect of resistance due to the 
RF. Much higher than the DC resistance and especially in your case which 
is going to have an incredibly small DC resistance. The AC resistance 
will be at least 2 magnitudes greater at this frequency. Measure it and 
you'll see.

Anyway, I love coils that are truly out of the norm. Although ACR and Q 
is really an uncertainty, the remaining outputs are not related and 
should be good. Just get the misc surroundings close and do the test 
again far away from any objects (including the scope probe; position as 
far away as possible) and you'll find Javatc will be really close to 
measurement. I expect when doing that you'll find your 800kHz will 
increase to about 870kHz indicating a fundamental near 2.6Mhz.

Take care,
Bart

Tesla list wrote:

>---------- Forwarded message ----------
>Date: Wed, 19 Sep 2007 07:21:32 +0100
>From: Chris Swinson <list@xxxxxxxxxxxxxxxxxxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: Re: secondary frequency problem (fwd)
>
>Hi Bart,
>
>  
>
>>2.7MHz is closer to 3 than 2. If you build a coil that with a
>>fundamental frequency at 2.7MHz (calc), then you must have some means of
>>driving it with 2.7MHz if using a signal generator and scope setup. If
>>you can't get past 2MHz on your generator, how can you say that it
>>doesn't ring at 2.7MHz? This must be an really small coil. Do me a
>>    
>>
>
>Its going by other coils I have tested. normally just after the Fres the 
>voltage just keeps falling. I would knock up a 555 circuit though I don't 
>think they go past 2mhz. Saying that, If I was driving it on 800khz as a 
>harmonic, then my voltage gain experiments will not be valid. My x17 would 
>be based on the 800khz harmonic.... that's a good question, *is* 800khz a 
>harmonic of 2.7mhz ?
>
>
>
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>>favour, send me a Javatc output so I can see the details. Your probably
>>just reading lower harmonics at the moment.
>>    
>>
>
>http://www.future-technologies.co.uk/temp/javatc.pdf
>
>It looks like you fixed the DC resistance in the update too, I think last 
>time it came out as 3ohms.
>
>
>
>  
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>>A resonant transformer isn't a typical turns ratio transformer such as
>>an NST or other iron core transformer. This is a resonant transformer
>>where the output potential is a function of the resonant condition which
>>exist at the fundamental frequency. If you want to calc output, use the
>>capacitances or inductances as follows:
>>
>>Vout = Vin x sqrt(Cpri/Csec)
>>    
>>
>
>Thanks for that. I know about the calculations, I am just doing some low 
>voltage experiments just to collect some bits of data.
>
>
>  
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>>Typically, coil potentials range from 200kV to 500kV. Imagine if the
>>number of turns (pri and sec) were used. Say for example an average 1000
>>turn coil with 350kV output. This means the primary would have to have
>>350 turns! Can you imagine that? So, how do we get to 350kV with only
>>say 10 turns? The answer is resonance (or that point where the inductive
>>and capacitive reactances are minimum). At that point, we then get a
>>high current characteristic due to reduced overall impedance which in
>>turn provides the high output potential, so think of it as a function of
>>the coils reactances.
>>    
>>
>
>
>I have in part been trying to get my head about it. I think of it as when 
>the tank dumps its energy, it takes time to discharge. It creates a field 
>which pumps the secondary. The longer the field is there more "time" the 
>secondary is being pumped. However in order to pump efficiently they have to 
>be in tune. Probably a few technicalities more to it, but its how I look at 
>it.
>
>
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>>As far as the Q output? Way off for your coil I expect (and is why I
>>would really like to see your detail). Q is calc'd from the Fraga AC
>>resistance and it's this AC resistance which is probably off. The value
>>is usually good for coils greater than 3:1 h/d as stated in the help
>>output of Javatc. But, your coil I'm sure is small and there are no
>>actual Q measurements for a coil that small. If I were you, I would
>>ignore those two outputs and simply measure it yourself. Just click on
>>the Q text in front of the output box. I describe in the help file popup
>>how to measure Q. It is a difficult measurement as far as accuracy and
>>takes some practice. In my opinion, the greatest difficulty is equipment
>>resolution.
>>    
>>
>
>
>Q seems a bit of a problem to me. I wrote my own calculator to crunch the 
>numbers, though I used DC resistance for the Q measurement. I am not sure 
>but I am sure Tesla used DC resistance for Q. He had factors in 10,000 or 
>more. My coils is actually pretty large as you will see from the data.
>
>btw, as a suggestion, could the blue background be changed back to what it 
>was before the update, I think it was a light grey. The blue is a bit harsh 
>to the eyes and the red text turns into a bit of a blur. Sorry to be picky 
>:P
>
>Cheers,
>Chris
>
>
>
>
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>
>  
>
>>Take care,
>>Bart
>>    
>>
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