Radio broadcast .. (1922-30)

A New Factor in Radio Construction THE KINEMATIC REMOTE CONTROL By M. B. SLEEPER Sleeper Research Corporation, ENGINEERS WHO have been working on remote control for radio sets have produced a wide variety of exceed- ingly clever devices. We, at the Sleeper Research Corporation, found that it would be difficult, perhaps impossible, to out- rngineer some of the systems already in existence. As a general policy, anyway, it is al- ways well to forget others when you want to do something original. That was why we w i'nt back to pre-war times and set to work on a thirteen-year-old system, originally planned for airplane radio use, to make a piece of present-day merchandise. There, briefly, is the story of Kinematic remote; dial tuning. It isn't designed as a remarkable mechanism that does amazing things. It is only intended to meet a sales manager's requirements as a piece of mer- chandise. The only remarkable things about it are its simplicity, small size, and low cost. What the Kinematic Does Fig. 1 shows a Kinematic control IKJX. There is a dial, the scale of which corre sponds to the settings of the tuning con- densers. This is rotated by the knob on the left of the box. The right-hand knob regulates the volume control which is mounted in the set. The volume control is the standard Yaxley device fitted with an a.c. toggle switch which is thrown over, when the volume is cut down to zero, to turn off the current supply to the set. We feel that the proper place for the volume-control resistor is in the chassis—• not inside the control box—because it is not good engineering practise to run long leads belonging to the radio circuits, here and there around the house. Moreover, when such an arrangement is employed, it limits the system to the use of only one control box. Certainly any really useful system must be capable of controlling the set from two or three points, or up to a dozen if they are required. How It Operates In Figs. 2 and 3 are top and front views of a standard Sterling screen-grid chassis equipped with the Kinematic driving mechanisms. The mechanism at the left is geared to the shaft of the four-gang con- denser, while the one at the right moves the arm on the variable volume-control resistor. The contact arm, in turn, oper- ates the toggle switch controlling the power. These devices are referred to as driving mechanisms because, contrary to their TUNING DIAL VOID ME COMTROL si ON H OFF SWITCH TUNING CONTROL Fig. /— The Kinematic remote dial tuning unit. appearance, they are not motors. They simply serve to actuate the condensers in perfect synchronism with the rotation of the dial on the control box, following not only in speed but in degree of movement. This point is made because, although the driving mechanisms operate in both direc- tions, they are not to be confused with the systems which employ constant-speed, reversible motors. Such motors are con- trolled by two buttons, one to make the motor turn left and the other to make it turn right. Stations are tuned in by jug- gling the buttons back and forth. The disadvantage in this is due to the inertia of the armature. That is, if you want to make the condenser move only one-half a division, and you barely touch the button, the armature does not have time to start up. If you hold the button down long enough to start the armature, having started, inertia will cause it to turn the condenser too far. By eliminating inertia from the Kinematic device, and designing it to operate in synchronism with the control box dial, at any speed, the tuning condensers can be adjusted to an accuracy of greater than one-quarter of a division on the dial. Still finer settings can be obtained if it is considered necessary, but one-third or one-fourth of a division is sufficient for most sets. Importance of Accuracy The extreme accuracy of the Kinematic gives just as perfect and as close tuning at each box as can be obtained by hand at the set itself. One of the great difficulties with pre- selection devices is the problem of stop- ping the condensers at a given setting, re- peatedly over a period of months, right on the nose of each station. Any kind of con- tacts are subject to wear, and stops are moved slightly by repeated action, just enough to make a difference of plus or minus one-half the division or more. The result is that the adjustments require frequent re-setting. As this is a service which must be performed by a serviceman, and, as it is due to failure of the mechanism itself, the work must be done at the dealer's expense. As a result the cost of repeated re-settings may wipe out the profit from the installation. Another thing, beyond the control of the manufacturers—a change in the antenna, the lead-in, or a ground connection— may throw out all the settings. Nor is the frequency of the broadcasting stations ab- solutely constant. The stations are only limited by Radio Commission regulations to an accuracy of one kilocycle, and, at that, many stations vary beyond this lim- it. Thus pre-selected settings, no matter how perfect, do not assure perfect tuning. All these troubles are eliminated with synchronous dial tuning, but they are in- herent with remote pre-selection. In this, remote pre-selection differs from hand- operated automatic tuning, for with the hand type of control no harm is done if the selectors do not bring in each station on the peak, for when the selector button is pressed the tuning knob is also within TUNING MECHANISM .ON &' OFF / SWITCH VOLUME CONTROL MECHANISM Fig. 2 — Top view of standard Sterling chassis equipped with remote control mechanisms. Fig. 3 — Front view of chassis shows small sise of tun- ing mechanisms. JANUARY 1930 • • 149