Antenna Tilting Theory and Practice
Will angling an antenna upward improve reception?
Some people who are far away from desired stations get an improvement using slight tilting, and I've seen charts of recommended tilt based on distance to the transmission antenna. This has to do with the curvature of the earth and any obstructions in the way between the transmitter and the receiving antenna. Antenna tilting can work well for some people, but might have no effect at all for others. Tilting an antenna is a time consuming process since we're talking about a very small degree of arc to be adjusted each time you test.
If I, in the Vancouver area, am aiming for SeaTac stations, I need to bear in mind that 110 miles away a TV signal emanating horizontally from there is not arriving here horizontally, but rather with a slight upwards angle, so it is therefore theoretically most efficient to aim my antenna slightly downwards
to match the angle. Having said that, in real-life practical terms pointing the antenna downward usually means worse
reception! The usual method of tilting is to aim the antenna at the tops of the local trees and then testing, re-tilting, testing, repeating, etc. etc. to see if any improvement in signal strength is found.
Antennas on rotors are not good candidates for tilting. The tilt might be be efficient for one group of stations in one direction but not for others at a different bearing. For that reason tilting should rarely be used on rotor-mounted antennas
Another situation that might call for tilting is if your antenna is statically mounted in line of sight to a broadcast tower, in which case you would tilt the antenna to point right at the top of that tower and run your signal strength tests. If you're using line of sight, a yagi is simple since you can aim it like a rifle. For a bowtie reflector, use a carpenter's square with the long section heading straight out from the centre so you can aim it like a rifle.
I hope this helps, and if I find any of those tilt calculators I'll post it in this thread. Is there a particular aiming scenario you are thinking about, bsr2002?