so ive been going back and forth on this for a few weeks now and figured id just ask here because the club guys are pretty split on it. we're putting together a 2m repeater up on a ridge site, roughly 1800 feet elevation, pretty clear shot in most directions except a bit of tree cover to the northeast. the question is whether to go with a decent collinear - thinking a Comet GP-9 or maybe the Diamond X510 - versus just building or buying a 4 or 6 element yagi and accepting that we lose the omnidirectional coverage.

the repeater is mostly going to serve a valley that runs roughly north-south, so theoretically a yagi aimed down the valley makes some sense, but theres always someone operating from the east side hills or coming through on mobile and i dont want to leave them with nothing. the site already has a short tower stub, maybe 15 feet of Rohn 25, and we can get power up there but coax runs are going to be long - probably 100 feet of LMR-400 minimum to get from the cabinet to the antenna.

anyone run a setup like this and had to make the same call? curious what people actually found in practice vs what the math says.

the GP-9 is a solid antenna but i'd honestly think hard about whether you actually need 9dBd of gain pointing at the horizon when you've got 1800 feet of natural elevation doing most of the work for you. at that height a modest collinear like the X510 is going to cover that valley just fine, and the high angle radiation from a lower-gain antenna might actually help with the mobile stations coming over terrain. we had almost the exact same debate for a 70cm link repeater a couple years back and ended up going with a Diamond X700 on the basis that it was less critical about mount alignment than a high-gain collinear and way easier to troubleshoot when something eventually goes wrong.

the 100 feet of LMR-400 is fine for 2m, you're looking at maybe 1.5 to 2dB loss depending on connectors, not a killer. just make sure your connector work is solid and weatherproofed properly, that's where most sites fall apart over time - not the antenna choice.

yeah what he said about elevation doing the work. we have a machine at about 2200 feet on a commercial site and it runs a GP-15 which is overkill honestly, thing hears mobile stations that are basically in a hollow 40 miles out. a yagi just doesnt make sense unless you have a specific coverage problem you're trying to solve, like punching through terrain to one specific area. for general repeater use you want omni and you want reliable, and a well-installed collinear beats a fancier antenna with a sketchy mount every single time. also seconding the connector comment - i've seen more repeater issues traced back to a PL-259 that wicked moisture than anything to do with antenna selection.