The L and S band antennas on AO-51 are linearly polarized, so the best setup for both uplink and downlink on these bands with 51 would be one that is circularly polarized. LHCP or RHCP should not matter for just AO-51. I would pick RHCP in order to be compatible with future HEOs on L and S (P3E, ESEO, and Eagle). Remember the dish will flip the polarity of the feed, so the feed itself should be LHCP.
If you do go circular on your BBQ dish, you'll need to screen it in order to take full advantage of the circularity. The BBQ dishes have a lot more reflectivity in one plane than in the other. That being said, even a stock BBQ dish should hear AO-51 fine on S even some polarity fades.
73, Drew KO4MA
----- Original Message ----- From: "Mark Brueggemann K5LXP" brueggemail-k5lxp@yahoo.com To: AMSAT-BB@amsat.org Sent: Friday, November 17, 2006 5:58 PM Subject: [amsat-bb] Re: 1.2GHz and K5GNA BBQ Ant ??
In the course of my travels, I read about the K5GNA dish screening on K5OE's site:
http://members.aol.com/k5oe/K5GNA_dish.htm
According to the text you get 1.5dB from the screen.
As far as the 1.2GHz antenna, I've only got a couple responses. No real clear answer on whether linear or circular is an advantage, or if switching polarization is advantageous. Not sure if this info is so common no one is interested in answering, or if there are so few users of the mode, no one really knows. Nothing on the AMSAT site I could find. Individual web pages on the topic yield a vastly disparate range of configurations, so no clear path to follow there. I got a quantative value of 1kW ERP on 1.2 to work AO-51, and a source of yagi antennas from M2 and helix antennas from W7LRD.
Mark K5LXP Albuquerque, NM _______________________________________________ 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