Hi Bill,
> LB Celik also warns that toroidial baluns may be a weak link in this
> system, since they are being asked to transform a complex impedance. This
> could cause core saturation at modest power levels.
This is an unimportant point for results, but something that always "bugs"
me.
RF transformers and cores get hot because of flux density and high loss
tangent in the material, they usually reach curie temperature and fail long
before saturation is reached unless the duty cycle is very short (like a
pulse transmitter) or unless dc flowing through a winding is magnetizing
the core!
An open ended or air gap core improves saturation characteristics, but not
loss tangent. Usually it is more the "material problem" than a "core style
problem". 73 material rods will heat up and fail just as 73 material
toroids will when used in high flux density transformers (which is really
what the balun becomes when driving some complex impedances).
If you feel the core getting hot, it is most likely from loss tangent and
not saturation. For some reason, we just have taken on a habit of calling
it "saturation". It's quite common to design transformers with cores that
get very hot and have them operating far from saturation!
73 Tom
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|