> I want... a dual band 144/440 antenna on my 85' tower. > Can I get away with a fixed elevation of about 30 > degrees and horizontal polarization?
Three facts say that 30 degrees is the wrong angle. 1. The amount of time that LEO satellites are above 30 degrees is less than 20% of all view times. 2. You dont need gain when satellites are above 30 degrees because they are much closer and 6 to 10 dB STRONGER. 3) You DO need gain at the horizon where they are 6 to 10 dB WEAKER. So putting the beam at 30 degrees is counterproductive to LEO satellite reception, you will be giving up 3 dB where you need it most!. The answer is to elevate it to 15 degrees. 1) You still have all the gain on the horizon where you need it 2) You dont loose any gain from 0 to 30 degrees where you need it 80% of the time 3) you lose a dB or so above 40 deg where you DONT need it at all Etc. I dont know where the 30 degree angle came from, but it is pervasive through the literature, but is just plain wrong. The only time to use 30 degrees is if your antenna is so low that it cnanot see anything below 15 degrees anyway, and you are already missing out on 70% of all satellite view times. So if 15 deg and below is ocmpletely blocked, then OK, set it to 30, but it wouild be better to raise the antenna, and see the horizon where satellites spend most of their time. See the scale drawing on www.aprs.org/rotator1.html Oh, and it is better to be vertical because some satellites are magnetically stabilized and in the northern hemisphere, they will be more vertical than horizontal. See the plots on http://www.aprs.org/attitudes.html > I recognize that this is a compromise, but I'd like to avoid > the additional complexity of dealing with an azimuth rotor. Elevation rotator is absolutely not required for any LEO satellite. And since we do not have any working MEO or HEO or GEO satellites, then it is the simple way to go. Hope that helps. Bob, WB4APR > > Any thoughts appreciated. > > 73 de harry, W6DXO > > _______________________________________________ > Sent via amsat...@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...@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
