Multiband HF Dipole antenna‘s are always a challenge when space is limited. A full-size 80-meter dipole needs a lot of real estate, which is not possible for many radio amateurs. The 20–40–80 meter loaded dipole antenna shown in the diagram is a smart and practical solution. By using loading coils placed at calculated positions along the dipole, this antenna allows operation on three popular HF bands using a single antenna and a simple 1:1 balun.
This design is especially useful for amateurs who want reliable performance on 80 m, 40 m, and 20 m without using traps or complex switching systems.
Basic Working Principle
This antenna is a center-fed dipole with loading coils inserted on both legs. On 20 meters, most of the antenna wire is electrically active, and the coils have little effect. On 40 meters, part of the wire beyond the smaller coils becomes electrically shortened. On 80 meters, the full length of the wire plus all loading coils work together to make the antenna resonate.
In simple terms, the loading coils “slow down” the RF current, making the antenna behave like a longer wire than its physical length.
Multiband HF Dipole Antenna Structure and Dimensions
The antenna is symmetrical on both sides of the center feed point. Each side consists of straight wire sections and two loading coils.
From the center outward on each leg:
- A 6.30 meter wire section
- One inner loading coil (L2 on left, L3 on right)
- A 4.80 meter wire section
- One outer loading coil (L1 on left, L4 on right)
- A 1.47 meter end wire section up to the end insulator
This stepped structure allows proper resonance across three bands without mechanical switching.
Multiband HF Dipole Antenna – Loading Coil Construction
The loading coils are an important part of this antenna and must be made carefully.
All coils use:
- 20 mm plastic former
- 1 mm enamelled copper wire
Coil details:
- L1 and L4 (outer coils): 145 turns each
- L2 and L3 (inner coils): 50 turns each
The outer coils mainly help the antenna resonate on 80 meters, while the inner coils assist with 40-meter operation. On 20 meters, the coils have minimal influence.
Spacing the turns evenly and securing them properly is important for stability and repeatable tuning.
Feed Point and Balun
The antenna is fed at the center using a 1:1 current balun. This balun is essential because it:
- Maintains antenna symmetry
- Reduces common-mode current on the coax
- Improves radiation efficiency
- Helps keep RF out of the shack
The diagram shows the use of RG-213 coaxial cable, which is a good choice due to its low loss and ability to handle higher power.
Band Coverage and Performance
This antenna is designed for:
- 80 meters (typically phone and CW segments)
- 40 meters
- 20 meters
Because it is a loaded dipole:
- Bandwidth on 80 meters is narrower than a full-size dipole
- Bandwidth improves significantly on 40 and 20 meters
- Efficiency is very good when installed at sufficient height
With proper trimming and tuning, SWR can be kept within acceptable limits on all three bands.
This antenna offers a good balance between performance and simplicity. It avoids traps, does not need external tuners for basic operation, and covers three major HF bands with a single feed line. It is well suited for home stations, portable field setups, and amateurs who want multiband capability without complexity.
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