Ham Radio/SW quick super compact antenna - The Good old Broomstick Helical.
This antenna is cheap and easy to make, Back then it was only $10, today it's closer to $40 and can be made from all parts you can find at the local "home center" or big box home improvement stores.
A package of 3/4 inch long brass screws
A package of brass nuts, and Brass washers
Spool of 100 feet solid copper 14 AWG wire (Mine is THHN but that dont matter)
A 4" ductwork T cap , 6 inch is better but 4" works just fine.
Start by stripping the end of the copper wire back 1 inch. This is a lot easier to do now than later.
Drill a hole just big enough for the wire to poke inside the pipe, stick the end through about 2-3 inches worth. Now comes the hard part, Start wrapping helically around the pipe. Every time you stop tape the wire down tight in the direction that you are wrapping to help hold it tight. Right about now your hands are starting to hurt, by the time you are done they will hurt badly and ache for an hour afterwards. When I said this is the hard part I really mean it, this is only 100 feet so imagine how much this would hurt if you made a bigger one that would let you transmit nicely down at 160 meters as well. That would be about 500 feet around a 1 inch PVC pipe, so power through the pain stopping for breaks to rest your hands, you have about an hour of hand pain ahead oh you.Once you are done Tape it down tightly, we need to drill a hole for the big screw to electrically and mechanically attach the wire to. My end is messy, if you plan it right yours can exit the coil clean and wrap around the screw as if a professional did it. Take your time and it will look better than mine. I use two brass washers around the wire to make sure I get a LOT of contact. on the other side add a washer, two nuts, two washers and a last nut. This is where we will attach our feed line.On to the tophat, this is actually important to create a capacitance at the end of the antenna to eliminate static electricity noise. Trust me it really lowers the noise floor and increases the performance of the antenna, ideal would be 6" in diameter but all I could find was 4" on the shelves. You need to take some sandpaper and carefully sand the edge of this thing, it's a round razerblade right now and to be sure you dont cut your fingers off, sand the edge well until it feels smooth and soft. Now drill a hole in the center or as close as you can eyeball it. Install your 3/4 inch screw with a washer on the outside and inside, wrap the wire end around the screw, add another washer and nut, then tighten it down. You can now push it on the top stuffing the wire into the pipe. Comparing it to the 12 feet of speaker wire I was using as a test antenna it works fantastic. With a random chunk of wire I could not tune in WWWV time signal on 15Mhz. with this antenna it now comes in clearly with some light background static. This is in my office where it is 12 feet from 3 computers 10 networked devices and all other kinds of electrical noise. If you are interested in Shortwave listening or want to at least have an antenna that is small but functional to test the receiving
That's IT! your antenna is actually finished. cut the unused part off that you will not need. I left the blank part of the pipe long enough so that the top-hat sat at the top of my window frame in the room I was going to have my radio. If you want to use this outdoors and put it up in the air, you really need to protect it. the tape you used will release in the weather, so my recommendation is to get some good paint and spray the whole thing except for the feet wire connection. Then you can leave about 24" at the end to clamp to a mast so you can get it higher up in the air. Even 6 feet is enough to make a difference. A single wire feed line up to 9 feet long can be used with this, if you want to use a longer wire and possibly transmit with it, then run a twin lead and put some ground radials off the ground wire from the twin lead, you do need a good Antenna tuner to transmit from this antenna and only at low power levels.
Using the "broomstick" with resonant radials turns it into an excellent amateur radio antenna for a specific band... For example with 4 radials cut for the 15 meter amateur band and a 4 feet high broomstick. My design with only 100 feet of wire is not really enough for transmission on those lower bands, I strongly recommend adding a LOT more wire, 200 feet on 3/4 inch PVC is a good middle point for performance and size. I wanted to build mine from whatever I could find on the shelf on a sunday morning at my local home improvement store. If you want to make a perfect one I would go with a smaller 16 awg PVC coated solid wire and make sure you cover a full 5 feet of 3/4 PVC with very tight windings. Yes you can automate this and build a jig to wind the wire for you. and if you really want to experiment with these I strongly suggest going that route. make a way for a drill to spin the PVC while you build a sliding jig to hold the wire spool and feed the wire cleanly and close to the pipe so you can do it quickly and without pain. I have heard that commercial versions use enamel coated magnet/motor wire to get more wire on the antenna to make a more compact and higher performing antenna. and you can certainly do that as well. Bonus points if you can find some 1.25" Schedule 40 PVC to slide over the wound 3/4 to make a pvc casing and create a completely weatherproof version.
If you want to make a more optimized version, The helical distributed loading can be cleaned up a bit by winding it with different pitch.... starting with turns separated about 2 wire diameters at the base, going to one wire diameter separation at the middle, and ending with closely wound turns at the top of the antenna, were it connects to the top hat.The general rule to follow is to wind enough wire so that it makes a half wavelength at the lowest operating frequency you want the antenna to work at. The easiest way to do this would be to try and measure out how long the stick will be tightly wound and mark at the 1/3 mark. now mark the next third, but at a DOUBLE distance because you want the same number of windings, but they will have a 1 winding spacing making the distance double. Finally the last third will be the full length of what a tightly wound pole will be (double thickness spacing). You start to lose the "compact" size this way as you will end up with basically an antenna that is 3 time larger.