Abstract :
In the decade or so during which the problem of eliminating or at least reducing atmospheric disturbances has been given serious and systematic study we have learned, more or less definitely, what we can and cannot do in this direction. For example, we know that there are definite and cannot do in this direction. For example, we know that there are definite limits to what can be accomplished by frequency selection. We know that directional selectivity is of substantial value, particularly when the pre-dominant interference comes from a direction other than that of the desired signal, and we can calculate pretty well the gain to be expected from a given design. The object of this note is to analyze another arrangement which provides for high-frequency selection plus low-frequency balancing after detection. The broad idea of balancing out the interference is old, but I know of no general analysis of the arrangement. Furthermore the principle of balance has recently acquired fresh interest due to the system disclosed by Armstrong in which high-frequency selectivity and low-frequency balancing are essential features. Armstrong´s scheme is treated in more detail in the latter part of this paper. The conclusions of this study are entirely negative, that is, no appreciable gain is to be expected from balancing arrangements. This is quite in agreement with the conclusion drawn over ten years ago by John Mills as a result of a rather extended experimental study made for the Bell System.
