Re: Top-load altering Q-factor of secondary cct

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Gavin,

No, that is not a correct statement. Q may increase, but will usually 
decrease because toploads are typically large relative to the coil. 
Malcolm recently sent his data of Q measurements (very nice tables of 
well documented measurements).

http://hot-streamer.com/temp/CoilMeasurements.zip

There are times when the Q started to increase, but as the topload 
was raised higher above the coil, Q began to drop. In "most" cases, Q 
dropped without the initial increase. This is easier to see in the 
tables near the bottom of the data. The increase in Q appears to 
occur on toploads which are small relative to coil size.

By realizing the topload capacitance affects the current distribution 
near the loaded end and is reflected by variations in inductance, 
it's not hard to realize that Q may go either direction depending on 
relative size and shape of the topload. One observation is that this 
phenomenon appears to occur when a low capacity topload is near the 
coil end and more likely on tightly wound coils. For example, in the 
top section of the data there are 3 different coils measured. Coil 1 
and 2 show increases in Q and coil 3 shows a decrease in Q. But note, 
coil 1 and 2 are closewound and coil 3 is spacewound. Also note the 
coil sizes compared to the topload sizes.

With that said, I recently measured Q on my 8.5" x 39.75" coil with 
and without topload. Q dropped with the topload installed (a 9" x 30" 
toroid). I didn't perform topload position measurements, but now, I wish I had.

Take care,
Bart

Tesla list wrote:

> Original poster: Gav D <gdingley@xxxxxxxxx>
>
> Hi all,
> I read in a book written by Richard Hull that increasing the 
> top-load will increase Q-factor of a TC secondary. I assume there is 
> a limit to this set by Q= 1/R sqrt(L/C). Has anyone either 
> experienced this and/or know of any theory for why this happens?
>
> Thanks,
>
> Gavin