With 4G tests going on this, may be of use for anyone who needs a quick cheap filter, even if it isn't perfect.
A co ax o/c stub across the TV feeder will put a notch about 30 dB deep at it's L /4 resonant frequency. It should be in front of any amplification i.e masthead preamps, but not necessarily right at the aerial.
The wavelength for 800 MHz is 37.5 cm so the stub should be 9.375 cm reduced by the co-ax velocity factor, typically 85% i.e about 8 cm. The classic method is to is to cut 2 stubs slightly over length, connect one and prune gradually it for best results. The second stub is to get spot on when over-pruning the first results in overshooting ( Murphy's Law !!) Take care not to short circuit the cut end.
By coincidence the 3L /4 resonance is at 2400 MHz which would attenuate WiFi interference if this is a problem.