Question regarding flux speed and transformer operation

[gyulasun]

Hi void109,

Perhaps you wished to write you needed 0.25m between coils for a 299..MHz signal ?

The 299..MHz has about 1m wavelength, and a quarter wave is 25cm.
According to the text I quoted above, the flux travels 1/4 wavelength, induces BEMF, the counter flux also travels 1/4 wavelength so that all together 1/2 wavelength is involved which is 180 degree i.e. out of phase, right? 
This out of phase flux is needed because the original BEMF flux is out of phase too just because of Lenz law,  so summing them up you get in-phase flux hence signals.

What I think the problem is what material should be used to carry the flux to 1/4 wave?
Air is the worst flux conductor and whatever higher (higher than 1)  permeability material is considered, it should have low loss in the 300MHz range too. I know of high frequency powdered iron cores that may work at 300MHz though their permeability is between 4 and 10 or so. Suddenly I do not have a better suggestion, will ponder on it later.

rgds,  Gyula 

[void109]

Thanks for taking time to ponder this Gyula!

The reel of metglas I have is:

http://www.metglas.com/products/page5_1_2_4.htm

I think reading the technical specs that this will not be suited for this test?  It looks like it has very high losses in the Mhz range.

I also believe you are correct about the distance required - still being new to this topic I was having trouble wrapping my head around the interactions and I believe my mental imagery of the process was incorrect.  So for a 299..Mhz signal, I'm looking for a 0.5m CIRCUMFERENCE and 0.25m between the primary and secondary coils.

That's a large core!  I have a transformer core on its way here I ordered some month ago, dimensions 150mm x 100mm, which coincidentally works out to a circumference (outer) of 0.5m.  Unfortunately I dont know what type of material it is (from an auction) other than it is manufactured by metglas.

And there's still the problem of not having equipment that will let me view frequencies that high! 

[gyulasun]

Well, I do not think either the METGLAS core can work above a few hundred kHz (the core loss becomes prohibitive) and unfortunately the large core you are going to receive is in suspect too.

Maybe I am mistaken but for the usual power transformer purposes ferrite manufacturers do not make cores working on higher than a few MegaHertz.
Think of the switch mode power supply cores, nowadays the earlier some ten kHz working frequencies have been shifted up to near 1MHz or slightly beyond that.

There are the so called microwave ferrite materials working up to the 9-10GHz range but normally their shape is disc, triangular or rectangular, although some produce custom shapes like this French firm (found at random):
http://www.temex-ceramics.com/site/en/microwave-ferrites-cermatmenu-29.html
Their so called spinel ferrite may be considered, (see their data sheet) you would have to consult them on toroidal shape possibility, probably they make samples in toroidal shapes to measure and characterize the material, this is normally the procedure when manufacturing.


There are the so called transmission line transformers, they normally have (mainly) toroidal ferrite cores for that purpose and they can cover several hundred MHz range but they consist of tightly coupled twisted wire pairs or coaxial cable lines, do not work in the usual manner power transformers do.  Though they are worth studying...

So the problem is still the material, even if the microwave ferrites could be used, question is their prices if one has to order them in toroidal shape...

rgds,  Gyula

[arhitrade]

Transformer operation considering the second magnetic field