Correct, you only need one. You will probably need to put a sleeve on the J-pipe dish mount after you remove the dish to mount your antenna. The J-pipe is a bit larger in diameter than the clamp on most antennas.
You will find what you need in the chain link fence section of your hardware store, it looks like this:
Slide it inside the J-pipe half way, and secure it with 3 sturdy sheet metal screws, then clamp the antenna on the half sticking out.
In general I wouldn't recommend a Ge 24769 or similar antennas. That is especially true if any of your local channels broadcast in the VHF band. (Most people have at least 1.) To start out you should run a TV Fool for your location. If you post the URL for your report here, we can give you more help. Your address information will be hidden. Look at the column labeled "real." These are the actual radio frequency channels your stations broadcast on. 2-13 are VHF channels. 14-69 are UHF channels. The report will also give you the direction from which your channels are coming from and a predicted strength. Like I said before if you post the URL for your report we can give you more help.
This is what I received from TV Fool: http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id=e1c6a1dd86c9fd
I have learned a lot from reading the posts here. This is our first time ever tinkering with an outside antenna that our neighbor had no more use for. My husband was using the splitter from the directv and received no signal and I remembered what you said about it blocking the signal. I told him about using a different splitter we had on another TV, 5-900 and now the outside antenna connected to the smallest TV in the house is picking up about 6 channels thanks to you. We have 3 other TV's but I'll wait to see what you have to say about a new splitter. Do you think 5-1000 is enough for 4 TV's total? We are cancelling Directv because our bill escalated 3 times in one month and we didn't do anything to cause that. I'm prepared to do something different and pay the cost once and be through with it.
I think your splitter is fine. Can you tell us where your antenna is pointed? It looks like the best direction would be about 230 degrees. If you also post a photo of your antenna, we can give additional advice.