Which aspects affect the sensitivity of a receiver?

When I design a TV receiver, the sensitivity of the receiver is not good. I want to know which aspects affect the sensitivity of a receiver. Could anybody give me some help or introduce some book about these? Thank you very much.

A general formula for sensitivity level for any type of receiver is:
RX_Sens(dBm) = ?174(dBm) + 10*LOG[BW(Hz)] + NF(dB) + S/N(dB)

So the main factors that influence the sensitivity level are Thermal Noise, Bandwidth, Receiver Noise Figure and Signal to Noise ratio at the detector input.

Just remind, You have to dig out what is system itself contribution
NF or intefere contribution.