High Frequency Apparatus Page 40

40 HIGH FREQUENCY APPARATUS 1 Fig. 1.-Two forms of stationary spark gaps. The type at the right is fitted with radiating discs to dissipate the heat generated by the spark sometimes possible to obtain the nickel-steel rod in suitable lengths, however, and, in this event, it should most certainly be employed. If an air blast is directed against the electrodes and into the gap, the operation will be improved materially. The current of air serves not only to cool the electrodes but to wipe out any arc that may tend to form. The Rotary Gap.-In this type of gap, one electrode is stationary while the other rotates past it a certain number of times per second. The various modifications of this simple rotary gap are bewildering to contemplate and no attempt will be made to describe all of them. Suffice it to say that the rotating member may consist of a single disc of metal from the periphery of which pieces have been cut to form teeth; or it may be a disc of metal with metallic studs fastened to it to form the rotating electrodes; or it may be a disc of insulating material with metal studs passing entirely through it near the periphery; in the last instance, the stationary electrode will be in duplicate, with one on either side of the revolving disc. The advantages of the many types are mechanical rather than electrical. The builder, in selecting a certain type, will have to consider the limitations of his shop equipment. One is about as good as the other so far as results are concerned, and almost any rotary gap is better than even a good one of the stationary form.