MEASUREMENT OF DELA V DISTORTION 



259 



Radio Frequency Measurements 



The frequency range of a particular measuring equipment using the 

 circuits of Fig. 5 or Fig. 8 is determined only by the range of the oscillators 

 and the range over which the plugs and jacks and attenuators operate 

 with sufficiently low reflection coefficients. While this range is greater 

 than the IF range encountered in microwave repeaters, it does not include 

 the actual microwave frequencies. However, it has been found that 

 microwave components can be measured satisfactorily by using the circuit 

 shown in Fig. 10. In this circuit the measuring equipment is operated at 



d 



R-F 

 OSCILLATOR 



CONVERTER 



FILTER 



NETWORK 



TO BE 

 MEASURED 



CONVERTER 



DETECTOR 



OSCIL- 

 LATORS 



fr 



J 



ATTENUATORS 



> 



J 



AMPLIFIER 



CATHODE -RAY 

 OSCILLOSCOPE 



SLOTTED 

 COAXIAL 



AMPLIFIER 



DETECTOR 



PHASE 

 SHIFTER 



Fig. 10 — Method of using the intermediate frequency measuring circuit of Fig. 8 for 

 the measurement of radio frequency networks. 



IF, and the reference branch is unaltered. The measuring branch signal 

 is fed first to a converter where it is beat up to the desired microwave 

 frequency. The converter is followed by a filter which eliminates the 

 beating oscillator frequency and one of the beat frequencies. The filter 

 output is then applied to the microwave component under test. The 

 output of this is fed to another converter and converted back to IF by 

 beating with the same oscillator that was used in the first converter. This 

 process removes any variations in phase due to variations in the beating 

 oscillator if the connections from the beating oscillator to each converter 

 are of equal electrical length. 



Since considerable extra equipment is included in the measuring branch 

 in Fig. 10, it will usually be necessary to make a calibration run with the 



