The Suppression of Radio-Frequency Harmonics in Transmitters

In the present paper the harmonic components of the antenna current are determined in terms of the corresponding components of the plate current of the power amplifier of transmitters. After investigating the cause of harmonic currents and pointing out the difficulties arising in connection with an exact calculation of the harmonics of the field strength, the discussion is confined to the effect of the circuits inserted between plate and antenna circuit on the suppression of harmonics. Several types of circuits are considered and the current ratios of the harmonic antenna currents with respect to the fundamental are given. For better comparison, the results are tabulated. It has been found that, in general, the suppression of harmonics as given by the above ratio is proportional to the product of the volt-amperes in each individual circuit of the network and to a power of the order of the respective harmonic. Moreover, a general law has been derived, according to which for a given total volt-amperes of the whole filter network the optimum number of individual circuits can be determined. Finally the advantage of the push-pull amplifier and another circuit which inherently compensates harmonics has been discussed and also the detrimental effect of the distributed capacity of the coupling device which provides an undesired path for the harmonics has been described.