Ill Gil Q RESONANT CAVITIES 



429 



needed of suppressing the TM in the presence of the TE. Since the resonant 

 cavity is a cyHndcr, of varialjle length, tlie movable end plate (or reflector) 



FREQUENCY INDICATING DIAL 



'-INTEGRATING CONDENSER 

 Fig. 12 — Type of construction in a ^ kmc echo box. 



FREQUENCY 

 INDICATING DIAL 



PISTON ROD 



INPUT TRANSDUCER- 

 Fig. 13 — Type of construction in a ^ ktuc echo l)ox. 



can be moditied to include a gap at its [periphery. The gap perturbs the 

 resonant frequencies of the two modes by different amounts so that they 



