Wireless Work in Wartime 



XI. — Radio transmitters using 

 synchronous and quenched gaps 



By John V. L. Hogan 



IN last month's article the non-syn- 

 chronous operation of a rotary gap 

 in the wireless transmitter of Fig. 41 

 was decribed, for conditions which gave 

 two or three sparks for each half-cycle 

 of alternating current power. The curves 

 of condenser discharge are shown in 



Power Imnsf. 



fig.+l 



A diagram of a radio transmitter with a 

 rotary spark gap interposed in the apparatus 



Fig. 42, where the divisions along the 

 horizontal line represent six-hundredth 

 parts of a second. Since the dashed 

 wavy line shows the voltages at which 

 the gap will permit a spark to jump, as 

 time goes on, and the solid wavy line 

 indicates the potential available (in the 

 condenser) to produce a spark, it is 

 evident that the discharge must pass 

 whenever the two curves cross. 



If we now adjust the studs so that they 

 are somewhat nearer together, permitting 

 the spark to pass at a lower voltage (or if 

 we raise the maximum charging potential 

 to a higher value), it is clear that the 

 overlaps will occur more often and that 

 it will thus be possible to secure four sparks 

 in each half cycle of charging current. 

 By proper selection of the break-down 

 and charging voltages, by changing the 

 wave-form of the charging voltage, and 

 by using a power transformer which will 

 put energy into the condenser quickly 

 after each spark passes, it is possible 

 to get a large number of fairly regular 

 sparks per second with only a low fre- 

 quency of alternating current power. 



The curves of Fig. 42 are not complete, 

 since the secondary condenser voltage 

 will be bound to be reduced by the with- 

 drawal of energy for each spark; never- 

 theless, a sufficiently "quick" or closely- 

 coupled power transformer will build 

 it up again before the next sparking 

 time, so that the general conditions will 

 be as indicated. 



For every spark there will of course 

 be produced a group of radio frequency 

 alternating currents in the oscillation 

 circuit. With the non-synchronous meth- 

 od of operation these will not be of 

 the greatest power obtainable from the 

 same amount of input energy. This 

 is because the condenser is not dis- 

 charged at the instant it has been filled 

 to its fullest (maximum potential) point 

 for each spark. It has been pointed out 

 that for a given capacity, the amount of 

 charge depends upon the potential; 

 obviously, then, if the condenser is dis- 

 charged through the spark gap at a 

 voltage of 7500 there will be less energy 

 for conversion into oscillations than if the 

 charge is held until the full potential of 

 10,000 volts is reached. The greatest 

 utility of the non-synchronous method 

 lies in the fact that with it one is able 



Fig. « 



Time 



Curves showing the operation of the non- 

 synchronous spark gap for a wireless set 



to secure a fairly good and moderately 

 high-pitched spark tone from low fre- 

 quency alternating current, even though 

 at some sacrifice of conversion efficiency. 

 By adjusting the gap for best regularity 

 of operation, with the fewest possible 



9.37 



