My name is Jackson Richter. I am retired from Rockwell-Collins and worked in the engineering lab for 31 years. Since my retirement my interested have peaked in radio communications. Especially in antenna design. Thanks to anyone here that would give me a little more insight with my questions. The input impedance of a half wave dipole fed at the center in free space is 73 ohms with some reactance. I have been looking through a lot of data for a formula showing the input Impedance at various distances from the feed point. One in particular states from (Wikipedia) Radiation resistance = 73.1/ sin squared(kx) If the dipole is not driven at the center then the feed point will be higher. If the feed point is distance x from one end of the half wave (lambda/2) dipole, the radiation resistance relative to the feed point will be given by the above equation. My question is if the feed point is at the center which is the 90 degree point, since a have wave dipole would be 180 degrees. then the sin of 90 =1 and K would also have to be 1 for this formula to work. What is this value for K? thanks JR To be more exact the value for sin squared would have to be 1, for the 73 ohms to be valid in free space.