Examine figure This is the characteristic of a resonated transformer used in the if circuit The frequency modulated signal is fed

into this device and the sweep circuit is synchronized in such manner that the start of the sweep occurs when the frequency modulating condenser is at full capacity and the frequency is the lowest. The numbers upon curve A in figure 263 are reference figures to indicate the response of the circuit at the various frequencies. During one half of the sweep cycle, curve B is developed and during the remaining half of the sweep cycle, curve C is developed, curves B and C appearing simultaneously upon the screen. If you examine curves B and C, you

pREqoENCY IN kc.

Fig. 263. Development of an asymmetrical resonance curve of an i-f. transformer. The sweep circuit is so synchronized with the output of the frequency modulated oscillator that the lowest frequency, 450 kc., is at the start of the sweep and the highest frequency, 470 kc., occurs at the middle of the sweep.

pREqoENCY IN kc.

Fig. 263. Development of an asymmetrical resonance curve of an i-f. transformer. The sweep circuit is so synchronized with the output of the frequency modulated oscillator that the lowest frequency, 450 kc., is at the start of the sweep and the highest frequency, 470 kc., occurs at the middle of the sweep.

fcequency in kc

fcequency in kc will find that they are identical, with respect to frequency response characteristic. They appear different, because the direction of the frequency sweep is different for curve C than for curve B. This you can see if you examine the frequency change during the existence of the linear sweep cycle. First, the frequency sweeps from the lowest to the highest and then from the highest to the lowest. While the response of the circuit remains the same, the appearance of the response curve has undergone a change. Curve C is curve B turned over. You will further note, for comparison with the subsequent illustration, that the maximum peaks in the curve appear at the outside of the curve, whereas the lower peaks are on the inside of each curve.

Suppose that we synchronize the linear sweep with the highest frequency ; that is to say, the sweep cycle starts when the frequency modulating condenser is all out and as the sweep moves the spot across the screen, the frequency of the oscillator is being lowered. What type of curve would appear upon the screen for the same resonant circuit? Examine figure 264. The basic circuit is the same as on figure 263. Everything in the system is the same, except for the synchronization between the movement of the frequency modulating condenser and the linear sweep. Compare curves B and C in figures 263 and 264. The curves are identical, although they appear different. The two maxi-

Fig. 264. The sweep and the highest frequency, 470 kc., af the frequency modulated output of the oscillator coincide in this diagram, showing the development of the resonance curve of the same i-f. transformer in Fig. 263. Note that the resultant curves B and C are reversed with respect to those of Fig.

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