Understanding the Hexbeam

Hexbeam multiband tuning (Part 2)

20m 17m 15m 12m 10m
0 KHz (0.0") 0 KHz (0.0") 0 KHz (0.0") 0 KHz (0.0") 0 KHz (0.0")
0 KHz (0.0") 5 KHz (0.0") 20 KHz (0.1") 210 KHz (1.0")
0 KHz (0.0") 12 KHz (0.1") 45 KHz (0.3") 45 KHz (0.2")
3 KHz (0.0") 47 KHz (0.4") 25 KHz (0.1") 45 KHz (0.2")
40 KHz (0.6") 25 KHz (0.2") 10 KHz (0.0") 15 KHz (0.1")
37 KHz (0.3") 0 KHz (0.0") 8 KHz (0.0") 0 KHz (0.0")
5 KHz (0.1") 37 KHz (0.3") 90 KHz (0.6")
5 KHz (0.1") 62 KHz (0.6") 270 KHz (1.3")
15 KHz (0.2") 77 KHz (0.7") 105 KHz (0.4")
43 KHz (0.7") 60 KHz (0.4") 240 KHz (1.2")
54 KHz (0.8") 90 KHz (0.6") 80 KHz (0.3")
55 KHz (0.9") 60 KHz (0.3") 75 KHz (0.3")
47 KHz (0.4") 50 KHz (0.3") 220 KHz (1.1")
97 KHz (0.9") 53 KHz (0.4") 60 KHz (0.2")
87 KHz (0.8") 35 KHz (0.2") 35 KHz (0.1")
60 KHz (0.4") 25 KHz (0.1") 23 KHz (0.1")
15 KHz (0.2") 112 KHz (1.0")
45 KHz (0.7") 165 KHz (1.1")
60 KHz (0.9") 330 KHz (1.6")
65 KHz (1.0") 160 KHz (0.6")
67 KHz (0.6") 120 KHz (0.8")
105 KHz (1.0") 280 KHz (1.4")
122 KHz (1.1") 105 KHz (0.4")
90 KHz (0.6") 250 KHz (1.2")
120 KHz (0.8") 85 KHz (0.3")
80 KHz (0.4") 85 KHz (0.3")
75 KHz (1.2")
157 KHz (1.5")
200 KHz (1.4")
358 KHz (1.8")
165 KHz(0.6")

In Part 1 of this section on Multiband Tuning we saw that the proximity of the wire elements to one another in a multi-band Hexbeam has a de-tuning effect on the antenna. The interactions are complex and there is no simple way to predict the frequency shifts that will occur as different bands are omitted or included. We saw that the frequency shifts suffered by a Broadband Hexbeam are modest, whereas those of a Classic Hexbeam are larger and need to be taken into account by adjustment to its wire dimensions.

To help constructors determine the wire dimensions required for any particular multiband Classic Hexbeam, I have modelled all 31 possible band combinations; in each case I recorded how the frequency increased relative to a 5 band array, and I calculated the increase in wire dimensions that would be necessary to correct the frequency offset. The results are presented in the table, where the first figure in a cell is the frequency offset in KHz and the figure in parenthesis is the correction factor in inches.

The first line represents a 5 band array where, of course, the correction factors are all zero. The next 5 lines show the correction factors for all possible 4 band arrays, the next 10 lines all 3 band arrays; the next 10 lines all 2 band arrays; and the bottom 5 lines show the factors for monoband arrays.

By way of example, suppose you are interested in a three band 20/15/10 Classic Hexbeam. Locate the line in the table which has entries matching the bands of interest - in this case Line 11. The data in this line shows that, relative to a 5 band array, the 20m tuning will rise by 54 KHz, the 15m tuning will rise by 90 KHz, and the 10m tuning will rise by 80 KHz. If these offsets are unacceptable they can be corrected by adding 0.8 inches, 0.6 inches and 0.3 inches to the respective Driver and Reflector legs; the correction factors for Driver and Reflector end-spacings are so small as to be negligible. Complete wire dimensions for a 5 band array are shown on the Classic Hexbeam Basics page, to which these correction factors can be added.