We jump off from the carousel at the right point, but what cable length does it correspond to?
Well, in this case your carousel rotates clockwise, or “towards generator”, technically speaking. You start from the red dot, which is approximately at twelve o’clock, and let’s say your first blue dot is at one o’clock, which means you must rotate 30 degrees on a carousel.
So?
Since the transmission line with the length of half the wavelength gives you a 360 degrees rotation of the carousel, you length should be half the wavelength times (30/360), which is the wavelength divided by 24.
If we are talking about an antenna for 40m band, it is about 1.66m, right?
Right. But, when you are using a coax cable, do not forget the velocity factor, which is around 0.66 for a cable with polyethylene dielectric.
So, it will be about 1.1m.