[GroundUrMast]

There is some variation between loss calculators. However, a conservative estimate of loss at the top of the UHF band would be about 6 dB / 100' of RG-6. RG-11 would come in at about 4 dB / 100'. As the frequency gets lower, so does the loss. By the time you're down to the H-VHF range, the losses are about half that of the upper UHF band.

There's going to be some minor amount of loss associated with a splice, but if you use quality parts and good technique during assembly, there's no advantage or need to provide additional shielding. The estimated losses cited would account for the connectors. Good practice would include protecting connections from water intrusion when they may be exposed.

The best 2-way split is going to come in at about 3.5 dB of insertion loss. 3 dB is the theoretical perfect split of power (no losses in the components). For example, if you put 1 milli-watt of power into a splitter and got 0.5 milli-watts of power out each of the two output ports, the loss inside the splitter would be zero, the sum of the power output would equal the input. But the difference between the input and either output would be 3 dB (a factor of 2 or 1/2 depending on the direction you view it from). 0.5 dB of loss in real world components is doing very well. If your system can't tolerate 3.5 dB of loss, you'll need to add an amplifier ahead of the loss.

Trees are 'wild things'. If the loss was fixed and stable, trees and other vegetation would not pose the problem they do. The signal path fluctuation/variation caused by the movement of the foliage causes the dynamic equalizers in the tuner to have to frequently readjust to the changing conditions, this often results in data errors and loss of signal lock. Bottom line, there isn't a single answer to your question.