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The behavior of two types of gain-clamped semiconductor optical amplifiers under small-signal optical modulation is analyzed both numerically and experimentally. The small-signal gain as well as the crosstalk is investigated in two different injecting schemes. Dependence on mean input power and signal frequency is studied. The study reveals a strong dependence of the small-signal gain on the direction of the data signal as compared to the pump signal. The biggest difference between both amplifier types is found in the co-propagation scheme where the RF gain shows a clear resonance in the case the gain clamping is achieved by a longitudinal laser field which results in a decrease of the small-signal gain around the resonance frequency. The behavior of the crosstalk is similar in both cases, however still showing differences due to the origin of the gain clamping, which will be discussed. The experiments confirm the results found in the numerical study in all cases.