appropriate balun/connector for wideband biconical antenna

[whirlwindz]

I'm constructing a biconical antenna which is to operate in the 30MHz-3GHz frequency range (yes, its sizable!). I'm curious as to the best type of balun to implement as well as the best connector system to use.

Find attached a diagram of the antenna. Side-length is 30cm, and conical half-angle is 45 degrees. The radio receiver is located below (where the coaxial cable is leading to).

I was thinking about using an 'ugly/common-mode choke balun' which essentially involves covering part of the coax with ferrite beads.

Any ideas will be most appreciated.

 

[VEBill]

You probably don't even need the ferrite bead choke. Assuming symmetrical build and 360-degree contact of the shield to lower element, there would be nothing inherent to cause currents on the outside of the coax cable. Of course, if it was installed in an area with high levels of lower frequency RF, then you feedline might act as a monopole and in those circumstances a common-mode choke might help. But that's more of an EMI fix than a balun.

The interface to the feedline is the only tricky part of the build. Ideally you would have a machined assembly that meets the cones, and mounts the RF connector (probably N-type). The design should be constant impedance, including consideration of the dielectric properties of any insulators used. Electrical contact should be 360-degree.

Once you have the center piece made, the rest is easy.

 

[whirlwindz]

Thanks.

 

[Higgler]

Bicones never need baluns unless you feed it from the side. Just stick your coax in there. VSWR at the high end of the band might head towards 3:1.