so i've been going back and forth on this for a few weeks now and figured i'd just ask here because im going in circles reading old posts and antenna modeling forums that are way over my head at this point.

quick background — i have a repeater site on a hilltop about 1100ft elevation, pretty clear takeoff in most directions but there's a ridge to the northeast that blocks a few towns i'd really like to hit. the current antenna is a hustler G7 collinear, 7dbd gain, been up there maybe 6 years and honestly it's probably fine but we're doing some maintenance work on the tower next month so it seemed like a good time to reconsider the whole setup.

someone suggested we put up a yagi aimed at that northeast problem area instead and feed it off a separate port on the duplexer, which sounds reasonable on paper but im not sure how much gain we'd actually need to punch over that ridge vs just living with the coverage gap. the ridge isnt massive, maybe 200ft above the path between the repeater and those towns.

anyone run a similar split setup? how do you handle the pattern difference when a mobile comes out of the collinear coverage and transitions into the yagi sector, does it just work or is there handoff weirdness with the duplexer loading?

we ran something similar at our club's 2m machine years ago, had a DB224 omni plus a single 5el yagi off a hybrid combiner aimed at a valley about 15 miles out that the omni just couldn't reach properly. worked pretty well honestly, the main thing you have to watch is port isolation on the combiner — if you skimp on that you'll get intermod garbage coming back into the receiver and it takes forever to diagnose because it looks like random noise.

the transition you're worried about is basically a non-issue in practice. mobiles just hear the repeater louder when they're in the yagi footprint and quieter when theyre not, there's no actual handoff happening, it's passive. the duplexer doesnt know or care which antenna path the signal came from. where it gets complicated is if you're running two separate receive antennas going into a preamp combiner rather than a passive hybrid, then you really need to think about phasing and isolation more carefully. but if you're just combining TX only on both and using the collinear for RX, keep it simple.

honestly for a 200ft ridge obstruction a yagi might be overkill depending how far those towns are. if we're talking 8-10 miles the collinear might already be marginal there and a moderate gain yagi like a 6 or 8el would help a lot, but if the towns are only 4-5 miles out and its just the ridge blocking them you might get away with just tilting the antenna or even just a better feedline run to reduce losses first. old G7s can have pretty sad feedpoints after 6 years of weather, worth checking the SWR on the existing antenna before buying anything new.