The RF choke here is based on work done by G0TXQ.


A rf-choke is a device which “deals” with commen mode currents.

In short:

Most of us, use coax cable to bring the signal to the antenna .Now, a coax cable is a unbalanced feed line. Logical cause the inner diameter isn’t  equal to the outer diameter…not equal…not balanced.

A dipole for example is a balanced antenna both sides are equal.

So we are going from a un-balanced feed line over towards a balanced antenna. In such a case there could be a commen mode currents (this is just one of the examples).

Those currents run back on the outer shield of the cause causing trouble. (qrm etc)

In order to illuminate those currents one could place a device called a RF-choke.

If you use RG 213 UBX a RF choke is nothing more than 4 to 5 turns around a 10cm diameter.

Photo’s always works..

There you go.. a RF choke with a “choke” over a 1000 ohms.

With thanks to G3TXQ for providing the details.

Antenna information 27 Mhz