Variable Equalizers

HE use of equalizing structures to compensate for the variation in the phase and attenuation characteristics of transmission lines and other pieces of apparatus is well known in the communication art. Ordinarily, of course, an equalizer has a definite characteristic fixed by the apparatus with which it is to be associated. It may happen, however, that the characteristics demanded of the equalizer cannot be prescribed in advance, either because the characteristics of the associated apparatus are not known with sufficient precision, or because they vary with time. Examples are found in the equalization of transmission lines the exact lengths of which are unknown, or the characteristics of which may be affected by changes in temperature and humidity.