You have only one transition 75 ohms > 50 ohms. This will cause negligible loss (0.177 dB). Not worth using 75 ohms > 50 ohms convertor.
When 50 ohm is mixed with 75 ohm,
Reflection Coefficient Γ = (75-50)/(75+50) = 0.2
SWR = (1+Γ)/(1-Γ) = (1+0.2)/(1-0.2) = 1.2 / 0.8 = 1.5
Mismatch Loss in dB = -10 log (1 - Γ²) = -10 log (1 - 0.2²) = -10 log 0.96 = 0.177 dB
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