OK, here's my tin can collinear I built a couple years ago from the drawing on Sprut's page. I didn't spend any money on it, just used what was kicking around.
To start make a big clearance hole in the bottom of the can, but not so big your insulator won't cover it. The triangular piece of Plexiglass in the bottom right picture is what I used for an insulator, it was cut off a corner of something that broke if I remember right. Doesn't need to be that shape. Bend a small hook in one end of the wire you're going to use for the active element, then with that flat (or clamped in a vise) make a 90 degree bend. Then measure up 130 mm and start making the bends in Sprut's diagram. I used galvanized steel electric fence wire because I bought a 1/4 mile spool of it to make antennas with. You can solder to it when it's new, it's stiff enough to stand upright for this distance. Sort of nasty springy stuff, you might want to wear gloves until you get it tamed and bent straight.
You'll need a hole through your insulator for the machine screw that holds the wire on, make sure you can keep the parts connected to the antenna from shorting out on the can. Drill a couple more holes to bolt the insulator to the can. I used a tiny scrap of copper flashing with a hole punched in it as a terminal to solder the center lead of the coax to, and it's on the bolt that holds the antenna on. The coax here is RG-59 because I have a lot of it around (it was free), and it's all copper, both the braid and the center, so it's easy to solder. Scrape a bare spot on the inside of the can, use a 100 watt iron or gun and tin that ahead, I did an extra one here that turned out to be in the wrong place so I did another. Be careful of melting the coax inner insulation, tin everything ahead and let it cool, then heat just long enough to melt them together. You could do this without soldering at all, just use a couple crimp-on eyelets for the coax, but soldered is more reliable. I've been soldering since I was about 10, just don't solder with short pants on.
On the other end of the coax I used a screw-on BNC fitting, you can pick them up at Radio Shack or other places cheaper, be careful to follow the stripping guide. You could also use an end cut off a cable with BNCs on it. The connection to the dongle is made with a pigtail, you can find those on eBay or Aliexpress. They're sort of necessary to have around if you want to use anything other than the antenna that came with the dongle, you can find them under $2. I just ordered my 6th dongle, most have pigtails to BNC. There's a little scrap of sheet metal bolted to the side of the can, that's to put something heavy (like a book) on to hold the antenna right side up. The coax comes into the can through a hole I filed the burrs off, it's clamped with a scrap of plastic cut out of a frozen dinner tray. There's a little scrap of sheet metal on the top of the antenna bolt as a washer. Oh, it's an empty tunafish can, steel, not aluminum
I see planes in the air flying over New York City 175 km to the south, Albany 60 km to the west, Boston 145 km to the east. I don't see them on the ground at that distance, only if they have some altitude. I've never used the antenna outdoors, rarely near a window. I built it quickly but it's worked fairly well. I'm ready for another though.
Make a little jig with nails in a board for bending the wire around, bend up 2 and put them together and you've got more gain, plus you can make them for friends. 75 cm of wire each roughly. I wonder if you can stack multiple ones and also bring the impedance down, not sure about the directionality though, probably wouldn't be omni anymore. You'd need to stack them vertically I think, like a J-pole array. https://en.wikipedia.org/wiki/J-pole_antenna
and https://m0ukd.com/calculators/slim-jim- ... alculator/
J-poles are sold commercially in sets of 4 for VHF, every time you put 2 together in parallel you cut the impedance in half. So 300 -> 150 -> 75, perfect. You just have to get the phasing right. But use the wiring harness, not the j-poles.
But simpler: take Sprut's design and mirror it vertically, that's 300 ohms about. Now use 4 of those at the same height 1/2 or 1 wavelength apart and you can just connect the terminals in parallel and get back to 75 ohms.