Hi all,
 I need some words of wisdom and a bit of help about the
construction of a small toroid transformer.

First the antefact : I swapped recently my TS-850 for a TS-950SDX,
a very fine radio, but much less sensitive on the LF band than the TS-850.
Looking at the schematics, and doing some filter simulation with
Electronic Workbench, I think to have found the culprit, i.e. L3, a small
toroidal transfomer, with ratio 1:4, which is inserted in the signal path,
after the input attenuator, and before the filters bank. With all probability,
its  response at 136kHz leaves much to be desired. The TS-850 doesn't
have any such transformer, the signal goes straight to the filters.

So I have decided to replace it. Looking in the MiniCircuits catalog, I have
found what seems to be the ideal replacement, the T4-6T-KK81 model, which
has a -3dB response from 10kHz to 100MHz. Problem is that this transformer
is not carried in stock by the Italian distributor, and both they and the
MiniCircuits sales office have a minimum quantity amount for an order.

At this point the only choice is to build it myself. And this is were your help 
could
come in my rescue. I need to know what your experiences are in building
such a wideband kind of transformers. What is the best type of material,
caveats to not forget, optimal number of turns, you name it.

TNX for any help,

73  Alberto  I2PHD