I've been fiddling with a couple antenna things because I want to get some more permanent options in the air while I work on the home shack (you can get up to speed on that project by starting here and following the links at the end of each post.) and eventual tower project. As I was messing around, it dawned on me that the desk I am sitting right now, faces a window that looks over the top of our addition and into the back yard. The addition has a metal roof. Why not throw a random-wire end-fed into the trees across the back yard, and use the metal roof as a counterpoise?
End-fed antenna's usually need an unun to transform the high impedance of the end of the wire into something that the radio or tuner will be happy with. This usually means that a 9:1 unun is just the ticket. With that thought, when I should have been going to bed, I was making this little number out of scraps of wire and hardware from my garage, along with a couple bits from the electronics stash:
If you do a search on that internet thing for "9:1 unun" you'll find all kinds of diagrams, far better than what I could draw for you. I mostly wanted to share this because I was pleased with how I was able to make myself a "mini" 9:1 unun. I managed to squeeze the whole thing into a 3x2x1 project box. It won't handle high power, but for 100 watts or less here at home, or as another piece of ammo in the portable kit, I think it will be just the ticket!
Once I had the thing built, I threw a 650k resistor across the terminals (because that's what I had handy), and then put the antenna analyzer on it just to make sure I had the winding correct and had it wired correctly. It read at something in the neighborhood of 1.5:1 across the entire HF spectrum, so I'm gonna take that as a good sign! All that will be left to do is to attach an appropriately random length of wire to it, connect the counterpoise terminal to the roof, and hook it up to the rig to see what happens when it actually has some power applied.
Just for fun, here's a couple more pics of my handy-work as I threw it together:
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