How would you sum 2 signals, lets say that come from low impedance sources, one DC-10MHz, the other 10MHz to 500MHz, about 1Vpk-pk each
Output must be 50Ohms, the DC is important and cannot be lost. A passive way would be preferred but I guess op-amps could be an option.
Maybe some commercial Tektronix or HP use circuits to do this but I can't recall any..