In article ,
Charly wrote:

Dear all,

Usualy, people use 9:1 balun to connect a wire or dipole antenna to a 50 ohm
coax.

If I use a basic TV coax (75 ohms) I suspect I will need a 6:1 balun instead.
If
so, how many turns of wire should I use for primary and secondary windings ?

I don't know the impendance of the antenna connection of my radios (ATS 909 +
ICF SW100), so I intend to give a try with the coax I have in hand.

Thanks in advance for your help,

Charly

The 75 ohm coax will be going into the radios 50 ohm input so that's
another problem.

What part of the power supply did the toroid come from? A toroid from
the EMI filter part of the supply would probably work well. If you have
the test equipment you could put one turn on the toroid and measure the
inductance. Also you could check the inductance over frequency to see
where that particular toroid will work.

Barring that use the minimum turns for a 9:1 anyway. Use a twisted or
overlapping method to wind the core. The antenna wire impedance will
change based on the wire diameter and height above ground so you need to
calculate that before you know what impedance ratio you would need to
begin with. Some people confuse the reactance of the wire with the wires
characteristic impedance, which is what you are trying to match. The
reactance of the wire will change with frequency.

--
Telamon
Ventura, California