Hi Jeff, KE7ACY
If the satellite transmit and receive in circular polarization RHCP or LHCP then using horizontal polarization on the ground station is no bad both for the uplink and downlink because you loose only 3 dB in signal strenght but your linear antenna system is not complicated at all.
By the way if the satellite transmit in linear polarization then circular polarization on the ground station is mandatory otherwise receiving with linear polarization when the satellite and the ground polarizations are opposite you loose at list 20 dB into the QSB
Since the most part of actual LEO satellites uses circular polarization both receiving and transmitting then a horizontal polarization at the ground station is fully satisfactory in uplink and downlink for satellite work and as well for weak signal work particularly for a beginner satellite user.
Obviously switching polarization between H-V-RHCP and LHCP for the uplink and for the downlink is much better but it is a lot more complicated.
About the use or not of a elevation rotator with the actual LEO satellites a fixed elevation of 20 degres is a good compromise because when the satellite is overhead the attenuation decreases and the most part of the time in wich a LEO satellite during a pass is above 45 degrees elevation is very small.
73" de
i8CVS Domenico
----- Original Message ----- From: "Jeff Moore" tnetcenter@gmail.com To: amsat-bb@amsat.org Sent: Friday, March 18, 2011 9:13 PM Subject: [amsat-bb] Re: more antenna discussions....
Horizontally polarized beams will not work very well for satellite use. For maximum utility, I'd get crossed yagis set up to switch between horizontal,vertical, and circular polarization. Use the circular polarity to work the sats, horizontal polarity to do weak signal work, and vertical polarity to pull in those weak repeater and FM simplex signals.
The az/el rotor set up will work best and give you maximum flexibility in your set up with the least impact on your above roof aesthetics.
73, Jeff Moore -- KE7ACY CN94
On Fri, Mar 18, 2011 at 6:40 AM, zach hillerson qstick333@yahoo.com wrote:
I'm still struggling to figure out the best antenna configuration for me. I was originally planning (and now own) to use a Gulf Alpha dual band fixed at 15* elevation, but I am now having 2nd thoughts. Being limited to 1 roof top tower it might be prudent to get as much use out of the single mast as possible. If I go with 2 horizontally polarized linear antennas on a cross boom (1 ea. 2m and 440) could I use them for both satellites and weak signal work? Is there a downside to proceeding this way?
One concern that I have is that the horizontal antennas seem to have a somewhat limited frequency range, and I'm not sure of the impact. Also, is it prudent to go with separate azimuth and elevation rotators to allow for future expansion (6m etc...), although the separation required between booms is height prohibitive with 6m?
Is anyone running a setup similar to this? Are you happy? Any thoughts, opinions etc... would be appreciated,
Zach N4ERZ
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