I've done a lot of work over the years modelling air cored
coils - and they're hard enough to get right. Throw in a
core and it becomes a nightmare. So much depends on just
how you wind and layer the turns, the type of wire, core
properties. That's probably one challenge I'm not going
to rise to. I admit - I am reduced to trial and error!
Tomorrow I might try a 1:1:1 trifilar wind and use an L or
pi match to raise the Z. Troubles lurk when I try to use
more than about 1:2 turns ratio. If that fails I'll throw
in the towel and change to single ended. As you can tell,
it's the first time I've tried to make a broadband PA
with a ferrite transformer. I naively thought it would be
easy!
I must say, I'm having fun with this - it's over 10 years
since I last made a transmitter, and apart from these pesky
toroidal transformers, everything seems quite easy to do
at MF.
--
Paul Nicholson
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