High Frequency Apparatus Page 48

48 HIGH FREQUENCY APPARATUS Fig. 3. Two Oudin resonators placed side by side to produce very long sparks and mechanically. For portable purposes, the Oudin coil is the ideal type to use, particularly if it is desired to keep down weight and bulk and to have apparatus that will stand the hard knocks of road work. Proportions of Coils.-In the actual construction and subsequent use of some dozens of different types of high frequency coils, the author has evolved a few simple rules, which, for some inexplicable reason, appear to give the pass-word to the realm of successful coil building. While there is a perfectly good method by means of which these coils may be designed “on paper," through the medium of various formulae, all more or less complex, the average practical worker in this field will admit that the time-worn "rule of thumb" method is possessed of certain advantages in this case as in others, particularly when the results of "rule of thumb" calculation are carefully noted and the mediocre designs eliminated from future consideration. With this brief explanation or, perhaps, apology, for the use of the much used-and abused-rule of thumb,