Японский радиолюбитель JF1OZL предлагает вариант изготовления диполя.

Basic construction
See fig1! A pair of 9.5 meters long copper wire is stretched for another side. A pair of wires is called as elements. If the degree of each element is 180 degrees, then this antenna is called as a basic dipole antenna. See fig 5! In this case the elements is stretched not straight. It is called as an inverted Vee Dipole. One of this elements is connected to the inner wire of the coaxial feeder. Another one is connected to the outer shield wire of the coaxial feeder. Another side of the coaxial cable is connected to the M connector. See fig1! In this case , Bal-an is inserted between the coaxial cable and the elements. This bal-an improve the efficiency of the antenna.

Practical process of makeing it.
See fig 2! Cut a 1 meter enamel wire on the center of it! Twist them each other! Wind it on the hole of the troidal core 5 times! See fig4! On the other hand, prepare a pair of 9.8 meters long vinyl coated copper wires! One of it must be connected a "A" point of the bal-an. Another wire must be connected on the "B" point of the bal-an. On the other hand, prepare the 10 meters long coaxial cable! Inner wire of it must be connected on the "C" point of the bal-an. Outer shield wire of the coaxial cable must be connected on the "D" point of the bal-an. Make some holes on the film case , in order to insert the bal-an on it! Hang the bal-an on the roof of your house , useing the proper length of vinyl wire! Tie the element on the veranda and fence like fig 5 with a pair of vinyl wires! Care to keep distance between this antenna and some metal structure of your house!
I used a vinyl coated wires as the elements. But enamel coated wire is also applicable. Connect the M connector on the another side of the coaxial cable! Use a SWR meter! transmit with CW mode! Measure the SWR! If the SWR become about 1.2, it is good. If the SWR is bigger than 1.5, cut the element about 10cm! See fig 7! If the SWR become smaller than before you cut the wire , try it again one more times! If the SWR becomes bigger than before you cut it, then you must connect some another short wires on the edge of the elements. This process is called as CUT-AND-TRY. Anyway you must adjust the length of the element to get a good SWR.
Do not transmit while you cut the wire! You may get an electric shock. With the same reason, you must care to stretch the elements on the area not to be touched by the any person. Use the paste on the holes of the plastic case of bal-an, to stop the rain! Now you get the dipole antenna. In this case all the elements are located lower than the roof of my house. But if you can locate it higher, you can expect more effect. The higher ,the better. With this antenna and 4W QRP transceiver, I could contact with some American stations.

Half of element of the dipole antenna is calculated as a 23.7% of the wave length of the band. 40meter band antenna element is 9.5meters. But as you already know, you must start the adjustment from 24 or 25%. I will show you the standard length of it about some amateur band.