I was - many years ago - involved in hunting for TV transmitters with harmonics that could interfere with GPS in the UK - although we found some candidates, we didn't find any that caused substantial problems. However it is certainly possible for a TV transmitter to cause problems in GPS frequencies either due to its fundamental or harmonic. There is a really interesting paper on it -Interference of GPS signals: Influence of Licensed Transmitters on the GPS GPS Signal Quality in the Netherlands' Airspace. This is an old paper (2000) from two researchers at the Netherlands Research Laboratory. I can't post a link yet but if you type "NLR-TP-2000-226" in Google, it comes up as the third report..