Okay---but the 12-15 degree argument _assumes_ that the station has a view "to the horizon" that isn't tainted by trees, hills, and houses. In those circumstances, 30 deg might well be the better choice! I know it would be where my array is at currently.
So, the 12-15 degree "optimum" assumes a clear view to the horizon...right?? Mark N8MH On Tue, Apr 12, 2011 at 2:24 PM, Bob Bruninga <[email protected]> wrote: >> As I said, in the "goode olde dayes" we used >> 30 degree up tilt and it worked well... >> Lessening the up tilt may increase the gain >> for the lower angle passes but will also decrease >> the gain on the higher angle passes. So, it is a >> "trade off" no matter what you do! > > Sorry to sound like I am quibbling... but that last sentence implies the > idea of an equal "trade off". But the tradeoff is not equal at all and may > be missing the point here. > > A LEO satellite pass does not need gain at "higher angles" because the > satellite is by definition 2 or 3 times closer to the ground station (+6 to > +9dB stronger). But one does need the gain at lower angles where the > satellite is much further away. > > An up-tilt of 30 degrees is throwing away excess gain where it is not needed > (high angles) at the expense of low angles where every single dB -is- > needed. So there is no real tradeoff... A lower angle (about 15 degrees) > is more-or-less optimum for LEO's with fixed tilt and modest gain beams. > > To actually quantify the exact best angle (which will depend on the actual > beam's own beamwidth), it is simply to up-tilt the antenna no more than the > angle at which the gain on the horizon LOSES say less than 1 dB. Note, this > is not half the published "antenna beamwidth" which is usually a "3 dB" > beamwidth. It is much less than that, less than half the 1 dB beam width. > You can measure this by setting the beam no higher than the upangle that > loses less than 1 dB to a signal on the horizon.... > > Something like that... > Bob, WB4APR > > _______________________________________________ > Sent via [email protected]. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb > -- Mark L. Hammond [N8MH] _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
