High Frequency Apparatus Page 34

CHAPTER IV. THE OSCILLATION CONDENSER. The function of the high potential condenser in a set of high frequency apparatus is to take the high tension current from the transformer or induction coil, store it up until the "condensed" energy reaches a certain critical value, and then discharge the current across a suitable spark gap, thereby setting up electrical oscillations which constitute what is called the high frequency current. In its simplest practical form, the condenser consists of two sheets of tinfoil separated by a sheet of paper. Such a condenser will have a certain electrostatic capacity designated by the word "microfarad" or fraction or multiple thereof. The single sheet of paper with its foil coatings will have a capacity of but a small fraction of a microfarad or mfd. as it is abbreviated. By placing sheets of paper and tinfoil alternately in a pile and connecting the alternate leads from the foil in multiple, a condenser of practically any desired capacity may be made, the capacity increasing in direct proportion to the number of little condensers connected in multiple. On the other hand, if we take two identical condensers and connect them in series, the pair will have but half the capacity of either unit. High Potential Condensers.-If a high tension current were impressed upon the simple condenser just described, the paper insulator or "dielectric" would not stand the strain and the current would puncture the paper. Therefore, in 84