I've been going around and around concerning trying to reach a repeater that's blocked by roundly a thousand feet of a mountain. I've gotten dozens of suggestions ranging from "you need more power" to "put a Yagi on a mast and hook up your HT and you'll be fine".
One of those suggestions was to put a passive repeater on the intervening ridge, then aim a Yagi at that. I rejected that at first, because all the land on the ridge is privately owned and fenced in (due to past history of hang gliders getting hurt flying off the mountain). However, something else occurred to me in that regard.
As I understand it, what's been referred to as a "passive repeater" is nothing more or less than a half wave antenna, which will re-radiate (with some loss) any signal close to its resonant frequency. The loss is fairly high, but the radiation is omnidirectional, meaning it ought to reach down into the signal shadow from the mountain. And while I can't get up there to plant a pole with a meter of copper tube on it (or equivalent), I might not have to, because several others already have.
There are four repeaters already on that ridge (none of them connect to the group I want to access, however). If I aim a signal at one of those repeaters, its antenna ought to re-radiate as a passive, as long as the signal I send is well separated from the receive and transmit frequency of attached repeater -- and that qualification is assured, because I'd be sending on the frequency for a different repeater. The one I want to reach is on 146.865; one I use regularly up there is 145.470.
I already know this doesn't work with the antenna I have on my HT, but I should be able to get close to double the signal with a Yagi (3 dB over a short whip isn't a huge gain for a beam antenna).
My HT has plenty of power to key a repeater at the distance involved, if I have clear line of sight -- there's one I've worked from hilltops near home, at a distance of forty miles, which is 500 or so feet up a TV tower. What I don't know is whether the loss on a passive will be too much to reach a repeater at thirty miles after re-radiation -- or whether an antenna with a repeater attached will even work as a passive on a different frequency.