Hi..

By the things you wrote, I understand the transistor is
connect to the sensor unit.
then you afraid that most of the voltage will fall the wire
and not left for your circuit.
My suggestion is to use LM741, or some OP-AMP.
measure the voltage that reaches to the other side of the
cable, (lets say 1v, for a very long cable) connect it to
the +in, and connect the -in to 0.8v (by two resistors),
I recomend you to use a coax cable in this case.
Also
You can use an amplifier in the middle of the way.
Goodluck
OK