When I went to the market with my Sir Mr Sudhir Shah (VU2SVS) to buy materials for making an HF dipole antenna, this was my first question. “Sir, which is the best wire for making a Dipole Antenna.” He told me, “NEVER USE A SINGLE STRAND WIRE FOR ANTENNA RADIALS (Shielded or Non-Shielded) It is highly advisable not to use a single core copper wire like which is used for earthing of home wiring (18 Gauge or thicker)”.
Here is what he explained.
He says the core of a conductor offers greater resistance to an AC current flow compared to the resistance offered by the surface. In other words, the surface allows a greater amount of current flow compared to the core. This effect is called the ‘Skin Effect’.
Also, there is a circular current, which flows in the core which leads to the heating of the conductor. This current which flows in a circular pattern is called ‘Eddy Current.’
The heating of the conductor leads to heat energy losses to the atmosphere surrounding the conductor. These heat losses also called ‘Eddy Current Losses’, cannot be in any way acquired to do any useful work.
From the above notes, it will be observed that one should try and have a greater surface area to the conductor so that it facilitates a higher current flow along the surface. This can be easily achieved if a single core conductor is split into multiple strands whereby one generates a large amount of surface area, which leads to lower resistance and thus permits a greater current flow.
In other words, even after using the same quantity of copper you can achieve a greater surface area because of multiple strands and hence leading to a greater surface area, lowered resistance allowing more current flow. Hence it is advisable to use a multi-stranded wire to form the two arms of a dipole.
To understand the thickness (current carrying capacity) of the wire it is important to know the thickness of each strand & the No. of Strands. The thickness of the individual strand should be measured with an accurate micrometre.
At a slightly increased cost, he recommends using the six sq. Mm wire with 83 strands. The best company for wires are Finolex and Polycab.