This is the dual band ground plane antenna I made out of 6 aug copper wire and an SO-239 connector. I got the idea from NA4IT on eHAM.net. You can find the original plans here.
My antenna differs from his in that I used 6 aug copper wire instead of 3/32 welding rod, because that is what I had on hand, and I used terminals on the ends of the radials as opposed to soldering them to the SO-239. I did this for two reasons. If I need to disconnect the radials, I can simply unscrew them making it much easier to move. The second reason is, I am just not very good at soldering and you have to get the SO-239 very hot for it to stick.
I chose to make this antenna because I pretty much only talk on my local repeaters, the only other antennas I had were a dual band mag mount in my car and my Nagoya rubber duck on my Baofeng. Finally, this is my first antenna build and I wanted to see if it actually worked before I get more technical.
My first transmission was on the 70cm band and it worked flawlessly getting onto my local repeater. It also works perfectly on the 2m band. Because I live in a neighborhood with an HOA, I just leave it in my attic. This puts the antenna about 20 feet +/- in the air and I have been able to achieve simplex transmission on 440 up to about 6 miles on 20 watts. I have been able to use it very well with a repeater that is about 15 miles away, which is plenty for me because I have dozens of repeaters in the area. This is all done on my THT TY-9800 Quad Band Radio I keep in my attic.
Overall, this build has been very worthwhile for me. I am hitting my local repeaters much better and have good enough results using simplex for my needs. The hardest part is soldering the V aerial into the SO-239 centerpin.