You can make a dual band ground plane as simply as this: http://www.eham.net/articles/7005
If you prefer to buy, something like would work nicely: http://www.gigaparts.com/store.php?action=profile&sku=ZMF-1754
Or just put your Comet or other dual band vertical somewhere on your roof. Many people with flat roofs even use a mag mount over a large cookie pan or other sheet of metal.
In my (limited) experience, all vertical and omni directional antennas work about the same, including the expensive Eggbeaters. They work fine as long as the satellite is more than about 25 degrees elevation above the horizon, which for most people is good enough. If you get serious about the sats and want to work the lower elevations, an Arrow or other dual band yagi will be needed, and you will have to rotate it, either by hand or with a small rotator.
When you are ready to make a contact, remember that AO-51 is busy and you need to talk quickly and clearly, or else someone else will step all over you. You might want to start on a late night weekday pass when it's not so busy, weekend afternoons are the worst.
73, Bill
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