I've repaired several tools that way, including one pair of long handled loppers with 1/2" steel pipe. The TV antenna mast sounds like a better fit for both size and weight, and I even had one, but I didn't think of it.
What you want in a tool handle is light weight and strength, which is why wood is often ideal. In a striking tool like a hammer, axe, pick, or even a spade, a wooden handle also absorbs some of the impact instead of transmitting all of it to your hands, and arms and shoulders. Steel is great for strong, but lacks these other critical qualities. How are your steel handled spades for use? Heavy adds up. I used to own a 20 lb. sledgehammer which would have been perfect for some demolition jobs except that I couldn't swing it more than a few times without having to stop to catch my breath.