I have an omni-directional antenna on my TV that picks up quite a few channels, but because I was getting a lot of dropout, I put a yagi antenna on the roof. I lost some stations with the yagi so I put in a combiner with A/B switch to be able to use both antennas and switch between the two. But when I switch to the indoor, I no longer get all the stations. If I connect the indoor antenna directly to the TV, the stations are back. Would this be a problem with adding the the splitter/combiner? Extra cable length? Mixing RG6 and RG59 cables? (Sorry if I'm not using all the terms correctly.) Thanks for the help.
The A-B switch could certainly cost you some signal strength. You could replace it with a good quality splitter, used in reverse, to combine both antennas.
If the omni is not amplified then try replacing it with on that is. You could add a signal amp to the one you have but it might cost more than replacing the antenna.
RG59 loses more signal than RG6 but it would be on a per foot basis. Mixing them doesn't matter.
I would have suggested that you get an omnidirectional roof antenna if the transmitters are in different directions and use a signal amp to boost the incoming signal strength. Simpler and easier to use.