Determination of Range of Effectiveness of Transmitter Harmonic Output Filtering

The actual effectiveness of a transmitter harmonic filter, when inserted in the transmission line to the antenna, can vary over a wide range which extends both above and below the standard characteristic-impedance circuit insertion-loss values. The location in this range varies with interconnecting transmission line lengths. An example discussed here shows that the actual insertion loss of a 60 db filter could be anywhere between 10 db and 94 db. Furthermore, the transmitter harmonic power delivered to an antenna, in the absence of a filter, can also vary with the length of the interconnecting transmission line. These effects are produced by changes in mismatch loss which occur as the length of interconnecting transmission line is varied. The purpose of this paper is to show how to determine the range of variation of such effects. Included are some sample calculations and the results of limited experimental tests.