Okay, thanks everybody. Time to think about two antennas, which gets to two more questions:
(1) What do I need to look for to get a good A/B switch (probably a remote control weather-proof model)? I've seen reference to a jointenna signal combiner; is this a potential solution for me?
(2) What antenna to point at KQEH? I'd have to upgrade my mast for a big antenna like a CM 4228; could I use something lighter like a yagi-type antenna?