Lowest Frequency on which the
Antenna Will be Used (MHz)
Make Feedline an ODD Multiple of This Length in
Feet (1, 3, 5, 7, etc.)
VF is 0.88 (DX Engineering 300
Ω
ladder)
3.5
30.9
7
15.4
10.1
10.7
14
7.7
18
6.0
24.9
4.3
28
3.9
Table 1: 1/8-Wavelength Feedline Calculator
If you have excess ladder line, it can be zigzagged while suspended in air, but it can't be closer
than a few conductor widths to metallic objects and
should not be coiled.
If it is necessary to
pass closely to a metallic object, twist the line to partially balance the effect on both sides of the
feedline.
If you need additional feedline, 100 foot rolls of 300
Ω
feedline (DX Engineering part number
DXE-LL300-1C
) and a convenient line coupler (part number
DXE-LLC-1P
) are available. This
coupler includes a high impact, insulated splice block, ring terminals and stainless hardware,
permitting strong and consistent splices of ladder line. See
Figure 1.
Note: If using an external balun, the feedline length should be calculated to the balun.
Figure 1
:
Ladder Line Coupler
The wire elements are precut to the correct length and should not be trimmed.
- 5 -
Example: To use this antenna from 80m to 10m, the feedline should be in
odd
1/8-wavelength
multiples on 80m. The 80m band starts at 3.5 MHz. Therefore, 123/3.5=35.1. Our feedline
VF=0.88, so 35.1 x 0.88=30.9 ft. per 1/8-wavelength. If 90 feet is needed to get to our operating
position, the nearest
odd
multiple 1/8-wavelength length is 92.7 feet. (30.9 x 3). If we needed 110
feet, we would have to add to the feedline to achieve 154.5 feet (30.9 x 5) to maintain the
odd
1/8
th
multiple-rule for length
