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You can use a Ma Com brand amplifier IC and use their suggested circuit. Then if necessary, use their 300:50 ohm transformers to match tye 300 ohm twinlead to the 50 ohm required by their amplifier ICs.
If you want to send the DC up the line to the amplifier, you can use a capacitor and inductor to split off the power and signal paths at each end. The inductor should have a reactance of about 4 times the line impedance at the lowest frequency you intend to use.
Your choice of amplifier will be a tradeoff between noise figure and distortion. If you are in a remote area, use the amplifier with the lowest noise figure.