TV receivers have a threshold signal below which they will not work and this varies. Portable sets often have better quality receivers to be able to work with smaller aerials.
For aerials
this reviews their performance A while back I also found a site comparing the boxes and what signal they required to work.
We get some results
JVC TU-DB1 -80dBm
HUMAX F2 -70dBm
MATSUI DTR1 -82dBm
ECHOSTAR / ECHOVIEW -75dBm
Technisat Digipal2: QAM16= -85dBm, QAM64= -79dBm
Technisat Digicorder T1: QAM16=-85dBm, QAM64=-79dBm
DIGIFUSION FR101 -82dBm
HUMAX PVR 8000T -70dBm
Televes DTR7288 -75dBm
GOODMANS GDB4 & GDB3 -82dBm
SAGEM ITD64 -90dBm
What they is there is a huge difference between boxes and I have noted my Thomson box is no where near as good as my Panasonic TV and my PCi card in my PC is not as good as Thomson box.
So even if we knew how far away and what power was transmitted from your local transmitter no one could work out if you could receive the TV signal strong enough to view.
Interference also is a factor with Sky boxes, Freeview boxes, and games machines all having RF outputs which can degrade any signal.
So only method is to try it.