Here is a Noise Margin diagram for an outdoor antenna with and without a preamp with weak signals. As with an indoor antenna, the preamp not only compensates for distribution losses but also allows the reception of weaker signals than without a preamp; in this case from -2 dB NM to -7 dB NM. Only antenna gain can improve the NM to the point that the NF of the tuner is exceeded without a preamp or the NF of the preamp is exceeded with a preamp.