A couple of years back, I was thinking of getting a cellphone. One of the places I looked, had a link to this map. It was a lot like google maps (in that you can zoom in and see very close details) but it had all these layers over the top that indicated the kind of cell phone service and which carrier provided it. We could toggle the layers depending on what we wanted to see. It turns out that I'm in a dead zone for all but analogue signal (which most modern phones can't use).
For example, light green would be for analogue telephone coverage. Purple would be for G5 at such and such a speed. Yellow would be for a different speed.
you best bet is to check friends phones see who has signal! In my house our normal phones have big issues (an old nokia and a samsung flip phone) but the smart phone I use for work gets 4G and works as an internet connection if required. we're only 1km from the mast for the two old phones, but there is a hill in the way, we're nearly 10km from the smart phone's mast but it does fine as no hills.
Farmers know to never drive a tractor near a honey locust tree. But a tiny ad is okay:
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