In practice, a good commercial TV receiver will correctly receive signals down to about -85 dBm at the antenna leads. But you can certainly achieve better results. This figure depends on receiver self noise, bandwidth, and temperature, so that results way down to -110 dBm and lower can also be achieved, either by adding cost to lower receiver self noise, or add cooling, and so on, or by reducing the bandwidth.
This paper gives a good presentation of the factors involved:
The attached report should explain what you want to know... in terms of front-end receiver noise. After that, it's all about how your signal processing processes signal versus noise.
Technical Report Noise and Noise Figure for Radar Receivers
Yes, I fully agree with the standard formula to measure the platform noise level in a radio receiver. However, as is expected in RF related measurements,the variation even in two receivers of same type can be striking.
I am citing some data for different receivers. (i) 802.11b @2.45GHz=(-65 to -70)dBm; (ii) [email protected]=(-69 to -63)dBm; (iii) GSM@900MHz=( -41 to -42)dBm
Such range variation is to be remembered for receiver design and measurements.