richard8123 wrote:

Hi. I've seen construction details of a longwire magnetic UnUn made with
a T130-2 toroid. The T130-2 is trifilar wound, each of the 3 windings
are 9 turns. The windings are connected in series, so that the turns in
total are 27: Turns ratio is :1:3 and impedance ratio is 1:9.

Okay, but do I keep the same number of turns for each winding (9) if I
use a T68-2 toroid? Thanks.

In theory, you have to calculate the exact impedance of the primary or
secondary and match it to where you want it to go. For example, if you
are connecting a 50 ohm coax to the primary, you have to match it to
50 ohms, which would make the secondary 450 ohms.

In reality, there is not much that a few turns or an impedance mismatch
will do, so wind it the same way you would on the other toroid.

While you are at it, save yourself a lot of money and use RG-6 coax.

Also in reality, you may not notice any difference at all using the
transformer.

The famous article floating around usenet said that it was not needed
for "any modern receiver" and that was written 20 years ago.

You may also try a straight 1:9 transformer with the primary (high number
of turns) connected to the antenna and the other side to ground, and then the
secondary connected to the coax. This reduces noise by having a DC path to
ground and no DC connection between the antenna and the receiver.

Geoff.

--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379