In my experience polarity switching is certainly a benifit on V and U. On L and S I have had only RH circular and certainly on AO-40 where I had hundreds of QSO,s with L up and S down I never had any indication of requiring polarity reversal.
On AO-51 there certainly are fades and perhaps some polarity reversal is occuring. However with RH L and S antennas I can usually work from AOS to LOS.
For AO-51 a single 27 turn helix driven with 10 watts from your Icom 910 should work OK provided you dont lose more than a couple of watts in your feed line.
For high orbiters you will almost certainly need more ERP such as I have with a 4 x 27 turn helix array, which I am afraid would not fit on your 6 foot boom, but you could get an amplier.
Construction details for L band helix ants is in the March/April 2004 AMSAT Journal.
Clare VE3NPC
----- Original Message ----- From: "Mark Brueggemann K5LXP" brueggemail-k5lxp@yahoo.com To: AMSAT-BB@amsat.org Sent: Thursday, November 16, 2006 4:00 PM Subject: [amsat-bb] Practical L Band Antenna?
I am (and have been for a while now) in the throes of getting a satellite station set up. I currently have V and U circularly polarized yagis, and recently acquired a K5GNA barbecue dish and converter. What would be a practical antenna for 1.2GHz? A helix is the first thing that comes to mind, but is the ability to switch polarization important? I was told this was worthwhile for V/U, so I went through the extra trouble and expense to add that feature to those antennas. How important is polarity switching for L and S band?
I am limited to what will fit on a 6' horizontal fiberglass mast of a 5400 AZ/EL rotor, so I am interested in finding out what would be a modest performance antenna for 1.2GHz for A0-51, and potentially future birds. Rig is an Icom 910. Thanks.
Mark K5LXP Albuquerque, NM