False Echoes - Example

Suppose that the transformer of Section "Design of Pulse Transformers" were used in a line-type modulator with L_N = 50 μh, C_N = 0.02μf, R_I = √(50 · 400) = 141 ohms. J = 2.0. Using equation 142, for close echo,

Impedance ratios:

From ratio k₄ we see that the long-term backs wing is barely oscillatory. Hence some distant false echo is possible. In Fig. 255, minimum k₂ for close false echoes is 0.17. Since k₂ calculated above is 0.628, there are no close false echoes with this modulator. According to Fig. 235, the transformer has 56 per cent backswing. It can be improved by using 0.002 in. grain-oriented silicon steel having μ = 1,000 at 5,600 gauss. L_e then becomes 1,000 μh, Δ = 0.283, k₃ = 2.75, and k₄ = 1.39. Now there are no false echoes, distant or close, and the backswing is 30 per cent.