the 'mini' beam is a home built job that I put together just for trips to the bush. Its in 70cm.
I’ve made them for 2meters, 220, 1.2gig as well. The 440mhz works the best, for the size that is.
I had to make one, cuz there didn’t seem to be anything on the market that fit my need, at least at the time I made it many years ago. Most of the portable things out there were made by Hams to take to a field contest, sitting right next to there car. Some even have 40' portable masts to put them on. I don’t have that kind of luxury in packing. There is a few out there that are designed for “fox hunts” but they still seemed to big for me. I wanted SMALL. The kind of small, that I could put in my shirt pocket. I did need something to get OUT more power. In FM there are only three ways to increase your power output. More watts. More altitude. More antenna. (Even better, a focused antenna or beam) more watts brings more weight. A lot of weight! I would usually have the altitude in most of the areas I go hiking in. So that left antenna. I have been making antennas since I was a boy so its second nature to do so. Others might find this beyond there means. But trust me its not hard to do, with some basic understanding. Even after I could afford the worlds greats equipment, I still would try and use my home built stuff, cuz in making it you get a greater understanding of how things work. The road to your goal is not only fun but informative! And you end up with what YOU want instead of what someone else might want, and will have to adapt to.
Its made with the remits of a fiberglass walking stick that I had found. (Same as am aluminum one, just thin fiberglass. Its also tapered like the alum.) The top end was busted off and had sharp edges, the owner just tossed it on the trail in the Sierras and kept walking. At first I was just picking up someone else’s trash. Then like everything I do, an idea starts forming in my head. (I cant help it, it just does) Before I had hiked the next half mile I had it all figured out. Once I got home, I started to work. I cut the broken end off to make a ‘nice’ cut. Measured out the diameters to find were to cut, the smaller bottom part would fit inside the larger upper part. Telescoping, one inside of the other. Fully extended I think its only about 14" or so. The elements that go all the way though will hold the boom in place. Like a pin to hold the two pieces together in the middle. If they were not put in the exact spot every time it would affect the match on the antenna. I also found a small plastic cap that would fit on the small end of the fiberglass tube and lightly glued it on.
The other end I installed a small metal (round) right angle bracket that installed into the end of the tube, with a couple of small screws and some epoxy. This would make it possible to lash it to a stick and raise it above my head. (A lot of the length of bought antenna’s are the handles) A little more of the epoxy finished off the fiberglass ends on that side as well. That left the inside of the tube free to put the elements of the antenna into.
The elements are just some aluminum tubing that I got from the hobby store. Think it is 1/8" or 3/16" ? ...Thick walled tubing. On the 2 meter I made, I used old aluminum arrow shafts. The next one I made I used alum. Gun cleaning kit shafts! The first thing I did was to cut them in half, then drill and tap the holes in the ends to the right threads for the small “all thread” that would fit. With one end threaded and a short piece of all thread installed and crimped (so it wouldn’t come out) I screwed them together though the hole I had drilled into the fiberglass ‘boom’ , marked the sides of the boom on the aluminum and disassemble again. This make gave me my “stops” for the elements. With a little washer, and some very light brazing, I sweat the washer onto the elements. Then they where carefully trimmed to the right length. (I made one for a friend and used alum. Gun cleaning kit shafts. They already have the threaded ends on them!) The only thing that was left was the “gamma match” this is where the coax would attach with a BNC connecter. A gamma match is a short bar that the ungrounded coaxal feed runs through to match the impedance of the antenna to the 50 ohm load the radio puts out. The antenna it self was about 35ohms if I remember it right.
the last thing I did was measure out some very thin, flexible, RG-58. I cut it to just a little over one wavelength to allow the radio to load a whole wave before the antenna.
that’s it.........
It matched out at 1.2:1 I wasn’t complaining, my radios wernt either!
The math and the measurements. I will leave to you. The formulas are all common knowledge and readily available.
well maybe I can draw you a picture. The kid still has the camera. At least I hope he still has it... Just a minute........
Try this..........
here is a site that I just quickly found that might help a little in the understanding of basic construction of beam, yagi antennas.
posted
OK, thanks for the info. I am glad you made it and didn't purchase it. I'll give it a little thought and look up a yagi with a nice small boom in the antenna book. I've never built a yagi and I was hoping your mini beam was a wire antenna. I've built a few wire antennas and I have seen a couple of wire beams but most are large HF antennas. I almost built a 3 band HF beam last summer. The best things about wire antennas, they fit in a bag and they are almost unbreakable but they require trees. Ok, I got to check your link to the other post.
posted
"The best things about wire antennas, they fit in a bag and they are almost unbreakable but they require trees."
well that's why i made a pocket size yagi.
without coax, its about 7" long and 5/8" round. thats almost the size of the rubber duck that came with the HT. the 'rest of it is jjust a very sma. roll of coax. easly fits into your other shirt pocket.
i put it into a fanny pack with extra batts. and a bunch of other gear and dont even know its there till i need it
cant get much smaller than that.
it gets me a little over 3db. which is super over the rubber duck that is on a HT.
i kind of have a 'thing' for cool little HT's i only have two that are in the 'air band'
those are the ones thhat i take on hikes, for emergency use. now that the personal EPERB's are out, i was thinking about getting one of those. but then thats just another hunk of gear i will have to hump up the mountain. at least the radio is multi useful. the last thing i want is to be stuck in the situation were i would have to cut some body part off to get out!!!
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