Hello Andy,

Thanks,  I seem to have had some success using 3 X the number of turns
and  changing  from  77 compound to 79 compound. I think I follow your
formulae,  as  I  say, maths is my very weakest point, so what appears
simple to some is often a struggle here :(



> For transformers the core is not terribly critical provided you use
> a grade of ferrite designed for the frequency of interest.  And at LF that 
> means SMPSU cores


> If I see a certain size core being used in a 500W SMPSU then
> there's a pretty good chance a core of the same size is going to
> work OK in an LF Tx of the similar rating.   No data sheets or
> trying to work out temperature rises.   


> I just use whatever feels right and apply the V < 4.44F.N.A.B 
> absolutely rigorously, keeping B to less than 0.1 usually


> As for impedances:  well they're  just Z1/Z2 = SQRT(N1/N2)
> Use V = 4.44.F.N.A.B to give you turns min, then calculate N1 and N2 while 
> meeting that criteria


> Andy  G4JNT





-- 
Best regards,
 Chris                            mailto:[email protected]