Alexandre, a DC block functions as a series capacitor in your input signal path. This keeps DC out, but being a capacitor, also has a response at RF that resembles a high pass filter. The cutoff frequency depends on the capacitor value in the DC block. Measurements of RF signals will be affected near and below this cutoff frequency. You should look at the frequency response curve for the DC block to make sure it will not interfere with signals you intend to measure. You could look at the spec sheet or sweep the DC block with your E8285A like you would sweep a filter to confirm its response.
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73, Steve W9TN
