| 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 lengths are shorter. (PE
abt 94%, PVC abt 91%). The wire length is also
depending on the height and the ground properties. Allow fine tuning
by starting with abt 0.5 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 http://www.circuits.dk/calculator_single_layer_aircore.htm https://www.basictables.com/electronics/inductor/air-core-inductor 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 |
