I was curious about that myself because about 99% of the TV antennas I have seen were on the chimney. It is really the only substantial thing to hang an antenna on if you don't want to be drilling holes in the roof.
I grew up in the suburbs where rabbit ears were not that effective so everyone had an antenna on the chimney.
The one I had in Southern Md had a 10' stick of rigid on the chimney mount, a rotor and then another 10' EMT above that with an antenna mounted on it. There were guy wires on the rotor mount. I could get the Redskin games from Richmond on that rig (blacked out in Md).
That was long before cable.
