I have for your consideration this 50 Ohm Impedance, Pi Resistive Attenuator. Follow the table on the back of the pcb for value and location of the resistors for desired attenuation. (Note: as shown in the first picture, the input side of the attenuator is next to the 49.9 ohm resistor and the output side is next to the 0.1uF capacitor).
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