NEW TUNING DEVICE

Radio Record, Volume I, Issue 26, 13 January 1928, Page 13

NEW TUNING DEVICE

VOLUME AUTOMATICALLY ‘y! CONTROLLED. 4 An interesting new radio development ° was recently described by Harold A. Wheeler, of Johns Hopkins University, : in a paper which he read before the Institute of Radio Engineers in New York. : ‘he device he described is a new ' radio circuit arrangement which permits an automatic control of loudspeaker volume so that neither the detector nor any of the audio amplifier valve stages can become overloaded, In this way not only is distortion eliminated, but what is very important, distant signals, which fade rather badly, are controlled automatically so that the volume level must maintain a definite value.

BEADING IS CORRECTED. Fading signals have heretofore been a drawback to the use of sensitive multistage radio frequency receivers because cf the constantly changing levels of loudspeaker volume. ‘The device corrects these difficulties. The name ‘Ansliostat’"? has been selected for this device hy reason of its tendency to maintain the audible intensity at a constant value. However, actual control of intensity level is not accomplished witliin the audio amplifier system, but rather in one or more of the radio frequency stages. These results are obtained through the action of the receiver detector, or rectifier, which in turn applies a negative biasing voltage in proportion to the strength of the received signals to ene or more of the valves within the radio frequency stages In this way output volume is maintained at a definite standard.

MUST TUNE BY EYE. Of course for the case of fading signals, such a device can only control that signal element which is above the required volume level. Where sige nals fade to a low value or entirely disappear, it is apparent that neither the audiostat nor any other available device can correct the deficiency. Int consequence of the automatic control action it becomes difficult to tune by ear a receiving set equipped with the new improvement. The amplification is decreased as the response to the signal is increased by tuning and vice versa, so that the point of resonance is itidicated by minimum plate current in the neutralised stages of the radio frequency amplifier. In other words, tuning is accomplished by eve, instead of ear, through a visual indication of a milliameter connected in the plate circuit of the first valve. ‘his arrangement is employed as a resonance indicator and to give ‘an indication of relative signal intersities.