Linear Distortions in Broadcast Receivers and Their Compensation by Low-Frequency Equalization Devices

This paper shows how the selectivity as well as the processes in the detector and low-frequency part cause distortion in broadcast receivers. The chief cause of poor fidelity must be sought in the selectivity of the tuning means. This can be raised to high values by increasing the number of tuning circuits, and by improving the quality of the coils (sharpness of tuning). The need for many selection means and sharpness of tuning depends less on the desire for greater amplification than on the necessity of being able to make a good separation of radio transmissions which are close together. The usual tuning circuits show, qualitatively, the same character of frequency drop independent of the number and sharpness of tuned circuits. Therefore in order to separate side frequencies that are comparatively close together (neighboring transmitters), frequencies must be considerably weakened which are indispensable for tone-true reproduction. Consequently, this paper shows methods which, in the low-frequency part, equalize, for the most important frequencies, what is lost in the high-frequency part. These methods will become unnecessary only when it becomes possible to build cheap, reliable radio-frequency band filters with constant band width but variable average transmission range. This is not as simple as the names applied to all possible designs would lead us to believe.