454 



BELL SYSTEM TECHNICAL JOURNAL 



Methods of Use 



A wavemeter may be used as either a transmission or a reaction instru- 

 ment. In the former case (Fig. 10a) it is inserted directly in the trans- 

 mission path, so that substantially no through transmission occurs except at 

 resonance. In the latter case (Fig. 10b) the \\avemeter is coupled to the 

 transmission path or a branch circuit. W'lien the meter is tuned off reso- 

 nance it presents such a high impedance to the main path that its effect is 

 negligible. At resonance, however, it offers a lower impedance which 

 reflects energy in the main line so that less power reaches the detector and 



R.F. 



BYPASS 



COND 



J_VIDE 



_ )e:o 



(METERl -pcOND. 



R.F INPUT >- 



L 



Fig. 9 — Crystal detector for pulsed RF signals. 



TEST 

 SIGNAL 



^^^^ TEST 

 SIGNAL 



POWER 

 INDICATOR 



TRANSMISSION. TYPE b REACTION TYPE 



Fig. 10 — Types of frequency meter circuits. 



a dip in the reading occurs. For most applications the reaction arrangement 

 is preferable since the power transmitted when the wavemeter is off tune 

 may serve various purposes. For analysis of frequency spectrum the trans- 

 mission method is necessary. This method requires two couplings to the 

 wavemeter, which lowers the Q as compared with the reaction type. 

 Drive and Scale 



A direct dri^'e with a precision lead screw of the micrometer type is fre- 

 quently used. Accuracy of reading is insured by spring loading to minimize 

 backlash and by specifying close tolerances for threads and for concentricity 

 of plunger and cavity. The scale on a wavemeter must be fine enough to 

 permit utilization of the resolving power. The conventional micrometer 



