My new high-frequency (HF) antenna is a portable segmented dipole. With the changes in the propagation due to the sunspot cycle, I needed to be able to use the 80-meter band (3.5 MHz). My magnetic loop antenna does not tune below the 40-meter band (7 MHz).
I constructed the antenna using lengths of wire (see below). The lengths of the wire are connected as needed to change bands. The connection is carried out using copper alligator clips. Copper was chosen to avoid issues with corrosion. Unlike the magnetic loop antenna, the dipole is easily stored in a laptop bag.
| Segment | Band | Frequency | Dipole Length | Segment Length |
|---|---|---|---|---|
| 1 | 20 | 14.150 | 4.953 | 4.953 |
| 2 | 30 | 10.130 | 6.326 | 1.8796 |
| 3 | 40 | 7.100 | 9.8298 | 2.9972 |
| 4 | 75 | 3.950 | 17.17039 | 7.34059 |
| 5 | 80 | 3.600 | 18.77059 | 1.6002 |
Wire velocity is approximately 93% of the speed of light.
Length expressed in meters.
Frequency expressed in megahertz.
The two leads of the dipole are connected to a balun. The balun changes an unbalanced signal from coax to a balanced signal for the dipole wires. The balun is tied to the top of a fibreglass painter’s pole. The great length of the dipole requires that I drape excess wire along my fence. Draping the wire is not an ideal solution, but it allows the wire to be fully extended.
To change bands, the alligator clips are disconnected to shorten the overall length of the dipole antenna.
Many thanks to K7BFL for providing plans and an explanation of the antenna.