[Amps] Mica cap substitute \ alternative

[Tom W8JI]

> On Jul 12, 2006, at 2:13 AM, Peter Chadwick wrote:

> Yes, but WHY? What's the mechanism that allows mica to be 
> a  perfectly good insulator in other application, way way 
> up in  frequency?
> 73
>> Peter G3RZP

> It's called Dissipation Factor.  For example, Nylon, 
> Delrin and Vinyl  are excellent insulators at 50Hz, but at 
> 50MHz they are not.
>R L MEASURES, AG6K. 805-386-3734




Mica isn't bad at a "certain frequency", and the dissipation 
of one type of mica cannot be directly applied to the 
complex workings of a component. There are many mica caps 
that are quite good to 1GHz and beyond.

Small mica capacitors are actually quite good at radio 
frequencies. For example, CDE's small case snubber mica's 
handle up to 9 amperes RMS continuously.

The peak performance of a 100pF CDE silver mica is at 10MHz, 
where it has the lowest ESR (under 0.01 ohm ESR). Even at 
300MHz, ESR is under 1/10th of an ohm!

Silver micas and multilayer micas are commonly used in high 
current VHF and UHF high power applications. One example are 
the metal mica stacks used in VHF power amplifiers.

There is great danger in making hard "rules of fact" based 
only on personal opinion of what indirect or unrelated data 
might indicate.

See:

http://www.cde.com/

and look at Snubber Micas and other mica caps

73 Tom