# Common mode choke

Yesterday I took delivery of some materials for making / repairing
antennas. In the order were 2x FT240-43 toroids.

One I plan to use to make a 4:1 balun, which should be fitted to
the full wave 10m delta-loop in my attic.

Impedance on a loop antenna is around 200ohms and the transceiver
is expecting nearer 50ohms.  To bring it within tolerance for the
transceiver you need a 4:1 balun, 200ohms / 4 = 50ohms, you get the
idea...


The other I had decided to use for a common mode choke, to keep
common mode noise out of my rig and RF out of my home. These are
expensive to buy and easy to make.

A large type 43 toroid, some RG58 coaxial cable and a couple of
cable ties is ![all you need][1].

[1]: gopher://gopher.icu/I/images/common-mode-choke.jpg