Right you are, Paul. However, all it takes is several wavelength's of physical separation to reap all of the "diversity gain". Of course, that's not gain in the usual sense. Antenna diversity has been known of since the 1920s.
To get even more diversity, one could have two sets of H & V polarized antennas separated by several lambda's, driving 4 receivers. There's more to be done with polarization as well: Circular, both RH & LH. It is possibile to make omnidirectional CP antennas. FM broadcasters use a lot of them. They look like a bunch of arrows. Ok, here's my dream (large land, large wallet): Three sites spaced several lambda's apart. Each would have H omni, V omni, CPRH and CPLH. I'd want each antenna to have some omni gain. For H, I'd stack two or more of crossed dipoles (turnstile, they each have a gain zero dBd or less); for V, I'd stack two or four VHF-style folded dipoles 360 degrees around a mast; for the CP's, I'd use the FM broadcaster-style omni CP's stacked. I've always wanted a 10m antenna that would give me V, H, CPRH & CPLH at the flick of a switch. A pair of crossed Yagi's would give that & 2 flavors of linear slant polarization, too, 135 & 45 degrees. I'd cross 'em at 45 & 135 degrees to somewhat avoid metal mast coupling effects. Wish I had a really strong piece of fibreglas mast, say 1.25"x10' to avoid that. I think that a vert. pol. Yagi on a metal mast will throw its performance way off. The only proper way to do that is ti end-mount the yagi about 0.2 wavelengths from the mast. I see it a lot on VHF & UHF in point to point service. It's also possible to feed both sides of the same square Quad at the same time, with 2 sep. feedlines. You'd then combine them as with crossed Yagis. I knew a guy who had crossed Yagi's on 10 m. He told me that with F2 signals, the maximum signal would drift among the various polarizations, i.e. no one was always best. Then of course 12 identical receivers, I'd use, oh, Mitrek's or MaxTrac's. I think I'd not be inclined to use Micor or any of the Syntor radios because they are purpose-designed radios for quite wide freq. spreads. This necessarily makes for the compromise of a wider RF & mixer front end. I think I'd like maximum RF selectivity on both 10m and 6m (the latter esp. where TV ch. 2 is used on the air. Next would come the rx voting scheme. It'd have to be carefully designed (the squelch ct's, too, probably no Micor-style circuit here). Maybe a combination of quieting and signal strength would be used for rx selection or combining (see my earlier note). Motorola once (abt. 1960) had a squelch ct. which fed a bit of audio into the noise amp to inhibit squelch clamping on modulation. It also used a bit of both 1st & 2nd limiter levels in the mix. I don't know that it ever was commercialized. I can dream, can't I? --John WB0EQ/VE6 --- On Fri, 8/21/09, Paul Plack <[email protected]> wrote: From: Paul Plack <[email protected]> Subject: Re: [Repeater-Builder] Diversity FM reception To: [email protected] Date: Friday, August 21, 2009, 1:34 PM When I lived in Atlanta in the 80's I was a few miles from the local 10m repeater, and quickly noticed that distant stations which were fading on the repeater input had climbing signal strength at my location if I switched to the input. About the time they started getting ratty at my place, I could switch back to the repeater output, and they were solid there. I think, on 10m, voting receivers separated by a few miles could actually be of greater help for maintaining communications with distant stations than for local mobiles. 73, Paul, AE4KR ,_._,___
