I am working on tuning a new antenna... Using an analyzer, I can measure the resistance and reactance in the shack. Measuring these values at the antenna is quite difficult as it is suspeded in the air. Is it possible to calculate the resistance and reactance of the antenna (at the feedpoint) provided I know the length of the coax feedline and the properties of the feedline (velocity factor, etc.)? I have seen some formulas that appear to convert the impedance, but I don't see how to use those to calculate the resistive and reactive portions at the antenna given measurements in the shack.