Common information about baluns and coaxfilters


A balun is an electrical device that converts between a balanced signal (two signals working against each other where ground is irrelevant) and an unbalanced signal (a single signal working against ground or pseudo-ground). A balun can take many forms and may include devices that also transform impedances but need not do so. Transformer baluns can also be used to connect lines of differing impedance.

Coaxfilter (Common mode filter)

A coaxfilter (Common mode filter) forces equal currents between the inner - and outer conductor of a coaxial cable. This achieves an RF standard "cold" coaxial cable. If you try to "better" match the antenna with a built-in transceiver antenna tuner, standing waves will occur. Therefore, you should not perform this additional adjustment.

Mounting a coaxfilter (standing wave trap)


Depending on the used balun at the antenna, it is recommended to replace this to achive the function of balancing and to use the coaxfilter (Common mode filter) function simultaneously.


Before the coaxial cable enters the house and is connected to a stations ground, a coaxfilter (Common mode filter) should be installed. In this way broadband interference and standing waves are best eliminated.

With a balun like W1JR you can reach optimal balancing as well as optimal standing wave suppression. Because there are always discussions about the measurement technique, here are some explanations:


From the measurements described above, the following characteristics arise.