Wireless Work in Wartime 



X. — The Non- Synchronous Gap Radio Transmitter 

 By John V. L. llogaii 



HAVING taken up, in the previous 

 article, the general operation of the 

 spark gap and primary oscillation 

 circuit of a typical radio sending station, 

 further and more specific types of spark 

 gap may now be considered. In the il- 

 lustration Fig. 38, printed last month, was 

 shown a simple fixed air-cooled gap; and 



Tig. 59 



An old type of a rotary spark gap which has 

 been in general use for some time for wireless 



the accompanying Fig. 39 shows a type of 

 rotary spark gap which has had wide use. 

 This consists of a rotating conducting 

 arm A, having spark electrodes on both 

 ends and mounted upon a driving shaft so 

 that it may spin between two semi-cir- 

 cular frames B, B. Supported on the 

 frames are a number (in this instance ten) 

 of fixed, equally-spaced electrodes. The 

 five on one frame are connected together 

 and act as one terminal of the spark gap; 

 the other five form the other terminal, 

 being connected together in the same way. 

 The length of the studs and the separation 

 between them is so chosen that when the 

 rotating arm is almost directly in line 

 with any one pair there will be only two 

 short spark gaps in the circuit. If at 

 this time the transformer (and condenser) 

 voltage is near its maximum, sparks will 

 pass and the condenser will discharge with 

 oscillations, as previously explained. If 

 the rotating arm has passed out from a 

 position almost directly between two 

 stationary studs, however, not even the 

 maximum secondary potential of the 

 transformer can force a spark to jump. 



The Disk Rotary Gap 



Another type of rotary spark gap is 

 shown in Fig. 40. Here there are two 

 stationary terminals D and E, and be- 

 tween these there rotates a spoked wheel 

 F. Each spoke has a spark gap tip G 

 at its outer end; the length of the spokes 

 and their distance apart is selected so that 

 sparks can pass only when they are almost 

 directly in line with the stationary elec- 

 trodes. It is evident that these two types 

 of rotary spark gap have much in com- 

 mon; in both of them the gap length is 

 continually changing, and in both the gap 

 is cooled and kept clear of conducting 

 gases by the air circulation stirred up by 

 the rotating member. 



There are two general ways of using the 

 rotary spark gaps. The gap of Fig. 39 is 

 generally used according to one of these, 

 the "non-synchronous" method, and has 

 consequently come to be known as the 

 non-synchronous rotary gap. The second 

 type, of Fig. 40, has had its widest use 

 according to the second or "synchronous" 

 method, and is therefore often called the 

 synchronous rotary gap. Neither of 

 these names is strictly correct, however, 



Fig. 40 



The second type or synchronous method is 

 usually called the synchronous spark gap 



since there is no reason why either gap 

 should not be used according to either 

 the synchronous or non-synchronous 

 method. This will appear from an ex- 

 amination of the two types of operation. 



797 



