Two halves does not always make a whole

Antennas do not have to be resonant to work well, but it does make feeding them a little less complicated in general. When learning the basics it may make it easier to study resonant antennas first. It is my intention to stick with resonant antennas for a while longer. There may be exceptions as there is with anything.
The shortest resonant antenna is a half wave long. Remember a half wave in free space is determined by the formula 492/frequency in MHz. When confined to a wire, the speed changes and there are other effects that appear to change the speed. The sum total of all these effects is to reduce the length by about 5%. So you change the formula to 468 if you are using most kinds of wire. That means that a half wave of wire is determined by dividing 468 by the frequency in MHz. So for example on 1.850 MHZ (160 meter band) the length of a half wave of wire is 468/1.85 = 252.9 feet or about 253 feet. The formula for a half wave in a wire is not exact. Although the length depends primarily on the speed of the radio signal in the wire, the type of insulation and its thickness makes a big difference. There are also effects caused by the wire being close to the ground or any other conductor, even wood or tree branches. There is an effect due to the insulator at the end of the wire. Some of these effects, especially due to the insulation, are more pronounced the higher the frequency. This formula is also not good if the antenna is more than one half wave long. The formula was reduced from 492 to 468 for a one half wavelength wire that has two ends connected to an insulator. If the antenna is say, one wavelength long, there are still only two ends, but there is effectively a half wavelength of wire in the middle that has no open ends. That has an effect on the calculation. It turns out that a large part of the reason that a half wave wire antenna is physically shorter than a half wave in free space is due to the insulators at the two ends or the “end effects”. The way I see it, the ends will either have an insulator or be hanging loose. In either case there is an end effect of one sort or another. If you connect two half wave lengths of wire together, you will find that together they are shorter than they should be for full wave resonance. The calculation of each half wave was based on each length having two ends. Remember, a full wavelength of wire will be slightly longer than two half-wave lengths added together. This is not a big deal, but something to keep in mind if you are constructing a wire antenna longer than a half wave long.