All ceramics/glass ceramics are not created equal and the exact absorption
mechanism
will determine it's usability in an RF field. The closer one approaches alumina
(Al2O3) or fused silica (SiO2) the lower will be its loss tangent. In the
cookware
industry, e.g., Corningware (a glass that has been ceramed) is unusable in a
microwave while Correlle dinnerware (a complex multi-layer glass-ceramic) has no
problem. Likewise some plastics do fine while others may quickly achieve
meltdown or
sparks may fly (some have very lossy fillers). In the meantime, the µwave
"test"
(put a cup of water in a microwavable container in the unit at the same time,
BTW) is
a quick and usable but not very accurate test for losses.
73,
Tom - WA2BPE
"Ian White, G3SEK" wrote:
> Cleeve wrote:
> >Good morning,
> >
> > From time to time, I have noted requests for sources of ceramic coil,
> > or
> >choke forms......I would draw your attention to an article in the RSGB
> >magazine "Radcom" for August 2002, pages 38/39, this is an intersting, and
> >practical article, on the home production of such items, by Ted Garrot,
> >G0LMJ.
> >
> > The technique used is pottery "slip" casting, and photographs of
> > finished
> >items are included in the article......the only drawback, is that access to a
> >kiln is required, to "fire" the finished item, but local potters, or pottery
> >classes, might be asked to help.....sincerely, John. G3JVC.
>
> It's certainly very interesting - he has made some very nice plug-in
> ceramic coil formers of the good old-fashioned kind.
>
> However, it would be nice to see some results from the microwave-oven
> test, in comparison with other materials. I tried that some time ago
> with a selection of typical plastics used for RF applications, and also
> a "no-name" ceramic coil former. None of the samples got hot or caught
> fire, but the material that got warmest was the ceramic!
>
> No doubt there are as many different grades of ceramic as there are of
> plastics, each with its own level of RF performance. But I wonder if the
> high reputation of "ceramics" in general for RF hasn't been built
> largely upon their ability to operate at high temperatures... regardless
> of their actual losses?
>
> --
> 73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
> 'In Practice' columnist for RadCom (RSGB)
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