MAGNETRON PULLING 



403 



20 



-10 



-20 



-30 



-50 



-25 



25 50 75 100 



TEMPERATURE (°C) 



125 



Fig. 8-5 Frequency Stability of a Magnetron and Klystron vs. Ambient Temper- 

 ature. 



The response time of the AFC does not have to be very great to correct 

 for the frequency changes listed in Table 8-1. It is only required that; the 

 controlled frequency can be adjusted over the range. To obtain a wide 

 tuning range, control of both the klystron cavity resonator and the reflector 

 potential may be employed. In many cases only reflector control is required 

 if periodic adjustment to accommodate frequency scatter caused by tube 

 replacement and aging is allowed. 



Table 8-1 indicates that when a radar set is first energized it is usual for 

 the open-loop frequency error to be rather large. A wide pull in range is 

 therefore required. {Pull-in is the process whereby the error in receiver 

 tuning frequency existing at the instant of an off-frequency input signal is 

 reduced by the AFC operation.) 



8-5 MAGNETRON PULLING 



The single mode equivalent circut of a magnetron is shown in Fig. 8-6. 

 The magnetron is considered as a conventional self-excited power oscillator 

 with the L-C tank circuit inductively coupled to the output transmission 

 line. 



As will be discussed in Paragraph 11-1, loading mismatch can affect both 

 the frequency and power output of the magnetron. Transient variations of 

 the load admittance occur in scanning antenna-radome configurations. In a 

 conical scanning radar, load admittance variations occur with feedhorn 



