Hex Wire Beam Hint: Simple Current Balun Using Ferrite Beads

This is a simple low cost 1:1 current balun for use on the Hex Wire Beam. It will work on any antenna that requires a 1:1 balun. The Hex Wire Beam requires a 1:1 current balun to reduce the common mode current flow on the outside of the coax. This common mode current will distort the radiation patten of the antenna. The RF Choke uses six of the ferrite beads over the coax just before the feedline from the shack attaches to the 20 meter driver..

Coax sizes up to RG-8 / RG-213 will pass through
the beads.

Historically the rf choke impedance rule of thumb(ROT) is a five or ten to one common mode balun impedance. This ROT would suggest that a 500 ohm common mode impedance is enough for 50 ohm transmission line. But in practice the ROT impedance requirement can be any value, depending on the system voltage exciting the feedline and system common mode impedance.

Based on tests using a RF current meter(W8JI Homebrewed Meter) at multiple points along the coax six of the ferrites provide more than enough impedance for the a common mode choke on the hex wire beam antennas whether it is located at the feedpoint of the antenna or below the baseplate.

Theoretically placing the balun/rfchoke below the baseplate indicates that it can distort the pattern of the hex wire beam. On the air tests indicate there are no difference.

The first picture is the ferrite beads before waterproofing. The second is after heat shrink waterproofing of the ferrite beads.

As you can see this is very very simple and inexpensive.


Link to where you can purchase a ferrite balun kit

Keep On Building,

73,

Ron W4RDM
www.hexkit.com






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