Flashover and the popular ~132′ dipole with two wire line feed worked up the voltage seen looking into the feed line for a particular system configuration,
For convenience:
An NEC-4.2 model of a 40.23m dipole at 9m height above good ground, and a quarter wave of lossless 600Ω line was run to obtain a .s1p file of the impedance looking into the feed line.
Above is a plot of peak input voltage @ 1500W around the 80m band. If you are using 100W, voltage is approximately a quarter of that shown, but that is still quite substantial.
Now as mentioned, this is dependent on many factors, including feed line length.
Let’s look at a wider sweep with feed line length 40m, about twice that of the configuration above.
Above, that fixed the voltage problem in the 80m band, peak voltage is below 2000… but look at the 40m band. Voltage around 7MHz is around 4000Vpk.
So, with a bit of juggling, you might find a feed line length that is acceptable for both bands.
Realise that the longer the feed line, the narrower the sweet spots.
Now think about the challenge of finding a length that is an acceptable compromise for 8 HF bands.
Of course, lowering the power to 100W helps to find a solution that might work well on several bands,
Again: Antenna SYSTEMS should be treated as a system, and designed at that level rather that a hotch-potch of components that are not well integrated.
Several people have created tools to try to optimise a centre fed dipole with tuned feeders for several bands, and it will be seen that the ‘sweet’ lengths are very limiting… but beware, they are based on assumptions of height and ground type that might make them inapplicable to your own implementation.
I am not saying they are a bad antenna system, but that it is unrealistic to expect fixing only one parameter, the dipole wire length, and letting everything else vary will deliver an multi-band antenna system with acceptable driving voltages at high power. It is not the no-brainer often thought.