Radio Broadcast (May 1928-Apr 1929)

Automatic Tuning for the Radio Receiver By LEROY S. HUBBELL AN EXPERIMENTAL SET-UP OF THE HUBBELL AUTOMATIC TUNING CONTROL The photograph shows a rough model of the tuning control apparatus and the radio and detector circuits of the receiver. The motor in this illustration is much larger than necessary. The model shown is equipped tor tuning only to one broadcast station. For each additional station, two more cams, one on each shaft will be required and one additional relay for each station IF WE review the development of the mechanics of a radio receiving set we remember a panel resembling a small switchboard which had primary and secondary inductance switches, an A battery control switch, several variable condenser controls and other minor control switches. Gradually, over several years, these numerous controls began to disappear until now, on the panels of many of the recent designs, not more than three controls exist, namely, the on-off switch, a single dial for controlling the variable condensers, and sometimes a volume control. While there have been many improvements toward simplifying the tuning of a radio receiver, it is still necessary to manipulate a dial and if a particular station is desired it is necessary to consult a schedule. If no tuning schedule is available the settings are oftentimes haphazard. In a large number of cases, particularly in the metropolitan areas, the dial settings are usually confined to not more than five to ten stations. When one is comfortably seated, whether in a favorite armchair by the fireside or at the table enjoying a dinner or participating in a card game it is annoying to interrupt one's activity to adjust the radio to some other station in search of a more delectable program. The partial elimination of the multi-controls on the radio receiver has reduced immensely the trials and tribulations of many a lover of radio entertainment. Probably there will always be at least two controls, one for the station setting and another for the volume from the loud speaker. Take these two controls to the armchair by the fireside or to the table and the ideal radio entertainment is at hand. In this article we discuss a means for automatically tuning a radio receiver at a remote point, although the same equipment may be used in connection with a transmitting station where the tuning elements are adjustable. The advantages may be summarized as follows. 1 . The set may be tuned to any one of several definite stations by pressing a button. 2. The set may be controlled at any point of convenience. 3. The radio receiver may be housed in a closet or other out-of-way place reducing considerably the cost of expensive furniture. 4. An outdoor directional loop type antenna may be used instead of the present antenna. [Judged by present standards, Mr. Hubbell's automatic tuning mechanism has certain drawbacks, as well as obvious advantages. These limitations hold for all automatic tuning mechanisms with which we are familiar. The apparatus takes up considerable space, and although, as Mr. Hubbell suggests, the receiver and the tuning mechanism may be located elsewhere than in the living room or the den — or wherever receivers now in common use are located — it is necessary to place the automatic mechanism quite close to the radio apparatus and in most cases that involves rearranging at least the radio frequency and detector circuits of the receiver. Neither Mr. Hubbell's arrangement or any other can readily be applied to the average existing receiver. That is, of course, not a serious disadvantage, for it is not difficult to rearrange a "pet circuit" so that the relay tuning controls are operative. Cost, too, is a factor, but a very real gain in convenience is achieved which should equalize that. — Editor] THE APPARATUS USED THE equipment designed by the author for automatically tuning radio apparatus consists essentially of a small commercial type motor of about h.p. or less, depending on the number of stations the equipment must tune to, connected to a revolving iron disc through a reduction gear. The revolving iron disc is caused to engage at right angles another iron disc by means of an electro-magnet (magnetic clutch). The second disc is connected to a series of cams to which spring contacts engage. Two cams, one acting as a vernier to the other and a relay are f~\E LA TE there has been a considerable interest in the automatic tuning of radio receivers. Remote tuning control of radio transmitters has been used for some time, in various forms by both commercial and military radio stations, but until recently, little had been done to explore the possibilities in the radio receiver. This timely article by Mr. Hubbell describes the mechanical principles of the system which he has devised: the illustrations show a rough model. A commercial model would probably be quite different in arrangement and appearance. Practically, the device suggested by Mr. Hubbell is limited to the control of from ten to fifteen stations, but it does permit the manual control of the receiver at any time. No effort has been made to treat this subject from the constructional point of view. Our readers will nevertheless be interested in the description of the present method. All patent rights arc reserved by the author. — The Editor. required for each wavelength setting. If the radio apparatus has more than one variable control the clutch and cams are duplicated, but the motor and reduction gear are common to any number of controls. At a distance from the radio set there is a small button box which contains a button for each wavelength and associated with each button is a small display lamp to indicate the station to which the set is tuned. The button box also contains a rheostat or potentiometer for controlling the volume at the loud speaker. Except for the push buttons, display lamps and volume control switch, the tuning mechanism may be housed within the radio cabinet. For those who are not interested in distant stations and confine their entertainment to local broadcast programs it would be practical and desirable to place the radio equipment in a closet or other out-of-sight place thus reducing the cost of the receiver. In the accompanying Fig. 1 is shown the fundamentals underlying the operation of the automatic tuning equipment designed by the author. In the lower left hand side of the drawing is shown a revolving iron disc, Di, whose shaft is connected to a small motor (not shown) through a reduction gear. When the motor is energized, the iron disc to which it is connected revolves at about 60 revolutions per minute. Adjacent to this disc is another iron disc, D;, the axis of which is at right angles to the former. These two discs have about clearance between their edges. There is a magnet, Mi, mounted closely against the driving disc, but not touching it, with one of its poles facing the driven disc. There is a return pole piece on 72