Improved Cathode-ray tube method for the harmonic comparison of frequencies

Convenient arrangements for the superposition of a telephonic and a radio-frequency displacement of the light spot of a Cathode-Ray Tube are described. The arrangements include the following: - Circular or elliptical trace at a telephonic frequency to serve as a time axis. When great steadiness, and uniformity are desired, a valve-maintained tuning fork controls the rate of revolution of the light spot. Radial, circular and straight-line displacements at low radio or high audio-frequencies are next described and examples of the stationary patterns produced when these are superposed on the circular or elliptical time trace are given. A special application of the method to the delineation of wave forms consists in the superposition of a long narrow elliptical time displacement and a straight-line high-frequency displacement in a direction at right angles to the major axis of the ellipse. By this means a considerable portion of the time ellipse is nearly a straight line representing a uniform time axis. The wave shape at the high frequency then appears in normal form and may be made of quite considerable size. Some examples of each of the foregoing methods are given in the form of reproductions from prints made directly on pieces of bromide paper held down on the top of the Cathode-Ray Tube for a few seconds (3 to 10). A special case occurs when an oscillatory valve system is arranged with grid and anode circuits closely coupled and harmonically resonant to each other. Wave forms consisting of a fundamental and a resonant single harmonic can be produced in this manner. Examples of current wave shapes in the grid and anode circuits are given, together with the voltage wave shape induced in a loosely coupled untuned coil.