--- In [email protected], Nate Duehr <[EMAIL PROTECTED]> wrote: > > I don't think the comments about where you want to put your signal > apply as much as some folks would have you believe. Even though the > 408 pushes more gain to the horizon, it still is rated for something > like 7 degrees of vertical beamwidth to the 3 dB down points.
Ummm.... Nate maybe you got the numbers mixed up. The 420 would be the one with more gain to the horizon. And it's the one with the 7 degrees of vertical beamwidth. The 408 has a 14 degree vertical beamwidth. > During a local discussion here recently someone also pointed out that > the 408 and that other one with 10 dipoles (sheesh!) that they make > now, have a lot of really odd-ball types of coax in their harnesses > for the phasing, and there's a LOT of it. How much energy is really > making it to the dipoles in a 408, and how much is just radiated from > all that relatively lossy coax in the phasing harness itself? We'll > all never know, I guess. But there *has* to be some loss there. Sure there's loss in that there *sometimes* wierd coax. And a few minutes with a calculator one could take a good stab at the amount of loss in the harness. But we're seeing the published gain figures in the face of these losses, so I feel compelled to not concern myself about that too much. > Other's experiences with the 408 and other high-gain antennas not > reaching close-in stations very well make me wonder if something else > was going on. Multipath and various forms of fading can really be a > bear in urban or hilly environments. Again, I think you meant to say 420, no? > > 7 degrees down with 3 dB of difference in signal, right in close, > shouldn't make that much of a difference, since you're closer to the > repeater. I'll admit though, again, that the Sinclair 4-bay's numbers > for vertical beamwidth sure look a lot nicer for a building-top system > than the DB's... it has something like 9 more degrees of vertical > beamwidth to it's 3dB points. Yeah, that means some of our signal is > going up, where it's not needed... but with gain numbers similar to > the DB's and a wider beamwidth, doesn't that say something about the > antenna itself? Just my opinion... > > (That 7 degree number for the 408 is from memory, but you can get the > specs and do the triangle math yourself, pretty easily... fire up the > old pythagorean theorem and do some engineering... then decide. I ran > the numbers for the Sinclair 4-bay at our 11,440' MSL site that's over > 5000' HAAT, to see if down-tilt was needed. It had a MUCH larger > vertical beamwidth over the DB's, and the answer was, "not needed at > all". 1 degree of electrical down-tilt would have been nice, > perhaps... to push just a tiny bit more signal into Denver... but not > really necessary at all.) Nate, perhaps you could clarify that paragraph... Anyway, I was just comparing published vertical beamwidth numbers for various bands/manufacturers/gains. Within a degree or so, it doesn't matter who makes it, you'll find 14-16 degrees beamwidth for antennas rated at 6 dbd, U or V. And for antennas rated at 9 dbd you'll find them at around 7 degrees, U or V. Makes sense, since everyone starts out with the same applied RF, and since no manufacturer has yet to modify the laws of physics to their favor (though many try to convince you differently hehe), there has to be pretty much the same shape/beamwidth of the RF donut for the same gain at the horizon. (Omni antennas). I'm with you on liking the dipole antennas... Laryn K8TVZ
