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Re: Q?



Hi Ralph,
                You know how to get me on the soapbox :)


> Original Poster: Parpp807-at-aol-dot-com 
> 
> In a message dated 3/13/00 3:01:07 AM Central Standard Time,
tesla-at-pupman-dot-com 
> writes:
> 
> <<  I would go for minimum losses (read high Q) in anything
>  > > bearing in mind that there are always tradeoffs to be made >>
> 
> Hi Malcolm and Reinhard, I have been lurking in the background for
> fear of being trampled upon by giants. I suspect I started your
> thread by responding to a question about Q with a statement to the
> effect that while maximum Q or Figure of Merit is desirable in a
> CW coil, it is not always desirable in a disruptive coil. My
> thinking  :-)) being along the lines that a Tesla coil is a very
> broadly tuned device. In tuning my little VTTC and my bipolar I
> have used a signal generator and an oscilloscope. I find a very
> sharp f res for the secondary, but only a very broad response when
> I try to tune the entire system. From the little I can understand
> in Terman or Henney or Circ # 74, this is a confirmation of the
> broadband character of the Tesla system.

That response is a reflection of the degree of coupling that is 
required in order to get power transfer efficiency up (stop the gap 
wasting it all). It says nothing about the individual merits of the two 
coils. It is important to understand exactly how this response arises 
(Tesla described it well in his original notes). The double sideband 
response is caused by a progressive and more-or-less sinusoidal 
amplitude change in a signal oscillating at Fr. That is exactly what 
happens in the secondary when monitored in the time domain. The 
primary is a bit different due to the presence of a non-linear 
resistance (the gap). If one could monitor total energy in the system 
and assuming there were no losses other than the spark gap and no 
breakout, one would see a linearly decrementing sinusoid oscillating 
at Fr. In fact you can see this if you monitor the primary alone (and 
I might add that a good quality - read high L/C ratio - primary shows 
the linear decrement up well).

> It may also be a
> confirmation of the fact that I have never built a real TC the way
> you guys have.  :-)) If a TC is designed for max Q doesn't this
> waste a lot of the energy that is really being just thrown out to
> the secondary over a very broad spectrum, and shouldn't the TC be
> tuned to respond broadly to at least below the 3 Db point? 

No - the real-time dynamics tell the story - the primary rings at Fr as 
does the secondary and as the oscillation amplitude in one falls, it 
increases in the other. Decomposing the signal into the frequency 
domain throws away all time-related information and I think is a total 
red herring when it comes to understanding coil operation. That's 
my personal view anyway.

Regards,
Malcolm