Shortened dipole for 80 m band
published:
In May this year I obtained my amateur radio license, and I decided it was time to try building my first antenna: Shortened dipole for the 80 m band, approx. 2 × 14 m = 28 m total span (so it still fits in my garden).
The mechanical design went through 2 iterations after review feedback received from my fellow senior HAMs from my local radioclub.
Dipole design parameters
The wire lengths of the shortened dipole, the position of the coils relative to the center, and the coil inductance (including number of turns and diameter) were calculated using the online calculators at:
- Electrically Shortened Center-Fed Dipole Calculator – K7MEM
- Inductance Coil Design Calculator – K7MEM
Parameters:
- Center frequency: 3.700 MHz
- Total length: A = 28 m
- Distance from center to coil: B = 11.2 m
- Wire diameter: D = 1.784 mm (2.5 mm²)
- Loading coils: 54.3 µH
- Number of turns: 32
- Wire diameter: d = 1.8 mm
- Coil diameter: 90 mm
- Length: 115 mm
- Length-to-diameter ratio: 1.25 : 1
- Q factor: 792
Started with a slightly longer wire and then gradually trimmed it to tune it to the desired frequency (target: middle of SSB portion of the 80m band).
Mechanical construction
- Soft insulated wire, 2.5 mm²
- Loading coils: grey PVC sewer pipes
- Dipole center: IP56 enclosure with a 1:1 current balun / choke
(RG58, FT240-31, suitable for lower bands) - N connector
- Strain relief with wire guides, so the wire connection using cable lugs on both dipole terminals at the center is not mechanically stressed
- Similar strain relief on both ends of the dipole, with added plastic insulators.
The insulators have an extra hole on the far ends where a rope will be attached for further attachment
Dipole center with 1:1 balun:
Top view of the dipole center:
SWR as measured with dipole center at approx. 12 m height in an inverted-V configuration (both dipole ends reaching down towards each end of the garden):
Dipole setup in the garden
In an inverted-V config:
