But by calculating for one frequency in the center of your phone band and another in the CW band, then cutting one half of the antenna for the phone frequency and the other for the CW frequency, the SWR is acceptable throughout the end of the entire band. If the SWR is not correct, lower the antenna and either shorten the antenna by pulling more wire through the insulator and rewrapping it onto itself or letting out more wire. Calculate the length of a 20 meter dipole, then simply attach the wires to the center insulator of the 75-80 meter dipole as shown in the drawing. Check the SWR and adjust if necessary. By tying them elsewhere there is less interference and less chance of tangles caused by the wind.
Some hams make spacers out of acrylic plastic to prevent tangles.
With a tuner, this antenna will work all bands. Next, build another dipole for 40 meters and add to it one at a time, dipoles for 15 meters and ten meters. Take time as you go and test each dipole as you go. Don't try to build them all at once, since tuning will be difficult with the interactions of the various elements. Now with two antennas and two feed lines you will be able to work all bands without a tuner.