7-20] PROBLEMS IN MEASUREMENT OF RECEIVER CHARACTERISTICS 391 



Demodulated 



Output 

 NoC+NoS 



■O NeC±NoS 



Output 



NoC±NeS 



Fig. 7-17 Ane;ular Error Demodulators. 



lent to a source temperature of 9775° K. Measurement of noise figure 

 merely involves the measurement of the noise power required to double 

 the output noise power of the receiver under test. 



A precision microwave attenuator is used to control the noise power 

 applied to the receiver. The available noise power from the discharge tube 

 is equivalent to a noise figure of 15.28 db referred to a temperature of 290°K. 

 The noise figure is determined by merely subtracting the attenuation 

 required to produce a doubling of the noise power from 15.28 db (corrections 

 for spurious signal response are required). 



Several problems arise in this type of measurement. If the noise power 

 output of the receiver is allowed to double, it is necessary that the receiver 

 be linear at the two output conditions and that the response of the detector 

 to noise be known. It is desirable that a 3-db loss be inserted in the receiver 

 rather than let the output noise level change. The 3-db loss must be inserted 

 at a point in the receiver which is preceded by sufficient gain that noise 

 sources following the pad do not contribute to the output. The receiver also 



