rjr@mgweed.UUCP (Bob Roehrig) (10/04/85)
The question concerns the formula given in the handbooks for determining the length of a half wave dipole. The handbooks say that dipole length in free space is determined by the formula: 492/MHz = feet. End effects on wire antennas reduce this figure by 5% so that the common figure used is 468/MHz = feet. Several friends and I have erected various antennas this year and have all independently arrived at the conclusion that 492 should be multiplied by This was observed during the installation of at least 3 antennas ( 80, 40 and 12 meter dipoles) all at different locations, and all at various heights. In every case, it meant shortening an antenna that was cut to length with the handbook formula. It made no difference if a balun was used or not, except that higher frequency antennas (say 20 meters and up) often have to be slightly shorter if a balun is used since inductance adds to the electrical length. If what we are seeing is real, where was the .95 factor derived from and why has it not been corrected? Bob, K9EUI