Much of the data below also applies to inductors in equipmentsuch as tank circuits. What does the coil do? A normal physically small physically small compared to antenna length or wavelength loading coil or loading inductor does not replace a missing fraction of a wavelength.
In the grander picture beyond ham radio, the quality factor is a value that describes some characteristics of an oscillating or resonating system. I get it! Q factor defines the damping of a resonator.
Wire coils inductive loads, traps, band-pass filters, etc. The free single-layer air-core inductor design tool by K7MEM will provide the construction parameters for specified target inductance values. There is an option available for taps.
This page describes the loading coil inductor that I built for my center-loaded meter 1. I attempted to build a high Q coil in order to minimize losses in the coil. The unfortunate fact is that loading coils for meter vertical antennas will almost always have enough loss to dissipate a significant percentage of the total power delivered to the antenna. This means that if you intend to operate at high power levels, the loading coil must be capable of dissipating it's share of that power.
Due to the tremendous response to my portable vertical antenna July QSTI've continued to evolve the design. Now, I've come up with a longer, lighter and more compact when disassembled antenna that is easier to build, and easier to find parts for. And band coverage is now 60 through 10 meters.
Rods, bars and slugs are commonly used in antenna application where narrow band is required. Rods, bars and slugs can be mde from ferrite, iron powder or phenolic free air. Ferrite rods and bars are the most popular type.