Re: [TCML] Flat strip primary inductance

[bartb <bartb@xxxxxxxxxxxxxxxx>]

Hi Finn,

The 1.5uH sounds correct (and I'm pretty sure it is). The ribbon is only 
2 turns and small. The inductance is therefore very small. I would bet 
that you have nearly 0.8uH of lead inductance from the meter affecting 
the measurement. It doesn't take much lead inductance to add to the 
total inductance of the LC on such a small coil inductance (and the 
value your off is about what you would see with the leads). If you have 
some old leads around that will fit in the Amprobe, cut those down to 
something short and measure again.

Also, metal sheeting directly under the coil can affect the inductance 
(shorted turn affect - but this would cause L to decrease). I doubt that 
is the issue but it can happen. This is easy to see (place aluminum foil 
directly under coil base, measure L, then slowly slide the foil out from 
under the coil and watch L change in the process.

Take care,
Bart


Finn Hammer wrote:
> All,
>
> I know this has been up before, but here goes:
> A flat strip primary has lower inductance than one made out of round 
> conductors. This is not new, but here is an extreme example, I think:
> I kept hanging tank capacitors on to the primary assembly, without 
> reaching the desired res. frequency. At last I had to investigate 
> further.
>
> The primary is an internal flat strip primary, for a BRISG coil, and 
> it consists of 2 turns 180mm dia with 5mm spacing.
>
> All simulators, INCA, javatc, wintesla predict 1.5µH and since the 
> primary cap is 7.5µF, the anticipated resonanse was 47kHz.
>
> However, the assembly resonated at 63kHz which corresponds to 0.8µH
>
> It baffels me that such an extreme difference could exist, so I made 
> up a sanity check:
>
> 2Turns of thich speaker wire, and a 7.5µF cap resonates at 43kHz.
>
> Has anybody experienced this before?
>
> A picture posted to see the primary, and the sanity check:
> http://www.hammertone.com/sanity.jpg
>
> Cheers, Finn Hammer
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