On 10/31/2015 4:33 AM, John S wrote:
On 10/30/2015 11:40 AM, rickman wrote:
On 10/30/2015 12:01 PM, John S wrote:
On 10/30/2015 10:46 AM, rickman wrote:
On 10/30/2015 9:07 AM, Jeff wrote:

I looked up some materials for fixed capacitors and found
dielectrics
with ?r change with temperature as low as 10 ppm/°C. These
materials
also have a loss tangent less than 0.001, some much less. I'm
wondering
if they would be practical to use for the dielectric in a variable
capacitor.

Me thinks you are overlooking the very high voltages involved.


I would have thought that glass was a good candidate and in plentiful
supply in various thicknesses, and would withstand very high voltages.
The Er is in the range 5 to 10 depending on the actual type.

It is the high voltages that makes the dielectric useful.


No, it is the increase in capacitance that makes the dielectric useful.

That sounds rather argumentative. I explain this in the next paragraph
which you seem to be agreeing with. So which is it?

Your posts are beginning to make me think you are a troll. Every person
who responds gets a provocative answer from you. If you already have in
mind the answer you want, why ask?

I don't know what you are talking about. If you think I am a troll, why
did you respond?

I am asking you if you believe what you wrote initially that the high
voltage does not make the dielectric useful, or if you believe what you
wrote subsequently that the high voltage issue *is* important. It's not
that important to me either way. I know what *I* think (and have been
consistent about it) and I am pretty sure I am correct. I just don't
know why you say I am wrong, then say I am right.

If you think my answer is provocative, please don't respond. If you
wish to discuss this then why not respond without the drama?

--

Rick