|Coil Loaded Dipole for 80 meter
This Coil Loaded Dipole might be a good option if your space is not big enough for a full size half wave 80m dipole. It is almost as good as a full size dipole. You can install it at a height from 10m to 20m or even lower. It is not the best DX antenna but it is very useful for local QSOs.
The total length is abt 18.8m for 3.680MHz. When using a a plastic covered wire the length is a bit shorter. The wire length is also depending on the height and the ground properties. Allow fine tuning by starting with abt 0.3 meter longer ends and fine tune to the best SWR by folding back the wire ends. You can install this dipole straight horizontal or in a inverted-V position.
The 50uH coil is a tightly wound coil on a plastic tube with a diameter from 50mm to 100mm. 1mm enamel cu wire (magnet wire) is good. The inductance is not so critical because you can adjust the antenna resonance with the length of end wires.
Here are some guidelines for 50uH coil with a tightly wound 1mm enamel wire.
Coil diameter 50mm: 33 turns
Coil diameter 75mm: 22 turns
Coil diameter 100mm: 18 turns
For the other coil diameter the amount of turns can be calculated with online calculators eg with these ones
The feeding point impedance is somewhat lower than 50 ohms depending on the height of the antenna and the coil losses. Thus the SWR is reasonable without an antenna tuner.
And don't forget a common mode balun in the feeding point! See more here
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