Hexbeam multiband tuning (Part 1)

Hexbeam photo

We saw in other sections that, compared to a full-size 2-element Yagi, Hexbeams are relatively narrow-band antennas - particularly the Classic version which needs to be tuned to deliver best performance at the frequencies which interest you. We will look in this section at how the tuning is affected when several band elements are brought together to form a multiband Hexbeam.

Shown below are tuning data charts for a 5 band (20m thru 10m) Broadband Hexbeam and a Classic Hexbeam. On each chart the extreme left-hand data is the frequency of best F/B ratio for the monoband element; the data to the right then shows progressively how the tuning changes as further band elements are added to the structure.

These data lead to the following conclusions:

It is probably unnecessary to tune a Broadband Hexbeam "in situ" because:

However, it is highly recommended that the Classic Hexbeam be tuned as described below.

The complexity of the interactions between the wires for the various bands makes it unrealistic to load the wires for one band onto the structure and "aim off" while tuning it to allow for the changes that will occur when other bands are added. I would strongly advocate loading all wires - Drivers and Reflectors - before beginning the tuning process. The objective is to get the antenna close to its final form so that as many of the interactions as possible are being taken into account.

We saw on the Classic Hexbeam - In depth page that tuning the antenna is a matter of trimming the Reflector until the peak F/B occurs at the frequency we require; and we must remember to trim the two halves of the Reflector by equal amounts. Any of the 4 tuning techniques described on the Classic Hexbeam Tuning page can be used succesfully on a multiband array, but note the following:

a) Reflector Resonance

b) Minimum Reflector SWR

c) Maximum Reflector current

d) SWR 1.4 times minimum

Part 2 of this Multiband Tuning section looks in more detail at the frequency offsets caused on a Classic Hexbeam by the interaction of band elements, and develops a set of correction factors from which the dimensions of any HF multiband Classic Hexbeam array can be determined.