Did you look at the antenna plot on that web page?: http://aprs.org/rotator1.html
At the proper 15 degree tilt of a fixed beam, the gain is down only 1 dB at the horizon. At your proposed 35 degree tilt, the gain is down 4 dB on the horizon where you need it most (70% of all pass times are below 22 degrees). To me, it makes no sense to sacrifice 4 dB in the area where the satellites spend most of their time. The only benefit to the high tilt angle is improved performance during the 3% of the time the satellite is above 60 degrees. And is that worth giving up gain for the 70% of all other pass times? Further, when the satellite is that high the signal is already 6 to 10 dB stronger than it was on the horizon anyway. How much better does one need to hear an already excellent signal? (so as to sacrifice the other 70%)? But again, if the antenna is in a hole and cannot see anywhere close to the horizon anyway, then of course, tilt the main beam up to point right at the lowest available horizon where the gain is needed most. Bob, WB4aPR > Bob, depending on the antenna pattern and the ground, as you say, > 15 degrees might be too low for any additional help toward the horizon. > 30 to 35 degrees will give you a little better results for stuff that isn't just > right at the horizon, I feel. As with all things in this hobby, experimentation > with your equipment will allow you to find the best combination. Also why sacrifice 3 dB for all terrestrial operations too which are also on the horizon? On 5/13/2013 11:29 AM, Robert Bruninga wrote: >> As has been said many times, most satellite passes are never >> "directly overhead", but rather on some inclination across the sky. >> A 5 element yagi antenna, at a 35 degree angle from the horizon, >> with only an asmuth rotator, will let you work far more satellites >> for > the money spent. > > Except that the correct angle is 15 degrees not 30 or 35. At 15 > degrees, the main gain lobe of the antenna still has excellent gain on > the horizon where you need it most and an equal gain all the way up to 30 > degrees or so. Below 30 degrees is where satellites spend 80+% of their > in-view times. This is where you need the gain most. But when the > satellite is above 30 degrees, the satellite is at least 6 to 10 dB > closer and so it makes no sense to sacrifice gain on the horizon > (where you need it most) by placing it at 30 degrees where you need it least. > > See http://aprs.org/rotator1.html > > Ignore the topic of the page but look very carefullyl at the SCALE > drawing (Yes, that is drawn to scale) of a LEO satellite pass Notice > how 95% of all satellite access times are below 50 degrees and 70% of > the time they are below 22 degrees. That is where you need the gain. > Do not waste it by tilting the antenna up more than 15 degrees. > > The only exception is that if your beam antenna cannot see the horizon > anyway, then, yes, tilt it up a little more since you wont hear the > low stuff anyway... > > Bob, WB4aPR > > > > Gregg Wonderly > > On 5/12/2013 12:48 PM, Jeff Moore wrote: >> I wouldn't recommend a J-pole for satellite work unless you expect to >> only work sats on the horizon. The J-Pole antenna has a low take-off >> angle and almost NO radiation overhead, an plain 1/4 wave ground >> plane antenna would work better for the sats. >> >> >> >> J-poles are great terrestrial communications antennas, not so much >> for working overhead satellite passes. An Eggbeater or quadrifiliar >> antenna would be a better choice. >> >> 7 3 >> >> Jeff Moore -- KE7ACY >> >> On 5/12/2013 8:00 AM, Werner, HB9BNK wrote >>> Thank you all for your valuable hints and advices ! >>> >>> I will now build such an antenna and then supply here the results. >>> >>> 73 Werner, HB9BNK >> >> _______________________________________________ >> Sent via AMSAT-BB@amsat.org. 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 >> > _______________________________________________ > Sent via AMSAT-BB@amsat.org. 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 > _______________________________________________ > Sent via AMSAT-BB@amsat.org. 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 > _______________________________________________ Sent via AMSAT-BB@amsat.org. 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
