improving wrong dimensions bicone - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: December 31, 2018, 03:37:05 pm
content: So my bicone antenna is built wrong, I used a 55 degree angle in the cone, and its dimensions are about 14x28 inches (taller then wide).I think the characteristic impedance is around 300 ohms. I have not solved its behavior past the characteristic impedance because the formulas provided by most documents I have require calculus and it does not use the same exact notation that I am familiar with, that is the equations are written in a way thats unclear for me in terms of how to derive or integrate things. I know how to solve DE and some basic MV calculus but I was kinda confused by the notations, I felt like I learned it with more elaboration on the setup. They seem 'gutted' to me.It is built to be fed directly into a coaxial line.It does look similar in dimensions to what would be considered appropriate for a balun fed bicone rather then a coaxial fed bicone.There is a coaxial connector soldered into the bottom of one of the cones, and it is already nicely mechanically fashioned in a 'hour glass' type mechanism with fiber glass rods and acrylic bases.However, I see that normal balun fed biconical antennas rely on the balun being placed between the cones sticking out in a T-shape.Can a balun be placed in a metal cylinder equipped with a BNC connector and reside in the hollow part of the cone?I was excited to built it and it looks good and it seemed to kinda work but I never tested it with a directivity bridge (like I have now). I am on vacation so I can't provide measurements but I might as well make the thread now.Also, does anyone have like, verified equations to use to solve for actual impedance, that you have tried out and worked? I am not asking for a exact solution but just how it looks like when you do it properly.

author: xyrtek
author_rank: Regular Contributor
timestamp: December 31, 2018, 06:19:05 pm
content: Antenna design and the math it requires can be daunting, for this particular antenna I can't say I have even used one.I am almost certain that you have done your googlefu so unless someone with experience in this particular type of antenna calculus chimes in or there is a calculator program somewhere in the obscure parts of the internet you have failed to look, experimentation is your next move.Do you have any sort of antenna analyzer?You probably think you don't but if you have a ham guy or gal near you then you do.Search for amateur radio clubs in your area, they tend to hide there sometimes.There are many approaches to hack your own antenna analyzer, and some kits can be had for really little $.http://www.foxdelta.com/products/aaz-0217.htmhttp://www.hamstack.com/hs_projects/k6bez_antenna_analyzer.pdf

author: coppercone2
author_rank: Super Contributor
timestamp: December 31, 2018, 06:21:32 pm
content: I can hook it up to a sweeper and do reflection measurement with a spectrum analyzer, however putting a balun on the side is going to require significant modification compared to putting it on the bottom inside of the cone where the coaxial connector is.I am just bored ATM in a crappy town in a meh country and there is a bunch of loud aggressive alcoholics outside the building I am in. Apparently confronting them is liable to start some kind of terror campaign of bottle throwing and fireworks. The bottles are piling up and I think its a good idea to stay indoors. They sound unusually fired up tonight. Known criminal records etc.

author: cdev
author_rank: Super Contributor
timestamp: January 01, 2019, 10:55:44 pm
content: I forget where I found this. In any case, its not mine!To avoid needing a balun you need whats called an infinite balun. Basically cover both the top and bottom with copper (ideally it should be rounded off like a sphere but thats impractical, so just cover it and ground the shield of the coax going down on its outside, where it goes through the bottom cap.)The impedance of this angle is "around" 50 ohms but I would suspect a bit higher. If you use individual rod elements the angle for 50 ohms needs to be greater- so the antenna should be even wider and shorter.Also in order to preserve the cone I think this design used conductive glue, not solder, at its tip.The reception/radiation pattern is best described as an oval that is enclosed by the two cones. You can make the cones asymmetrical to raise or lower the pattern (for receiving aircraft, lets say or things that are below the horizon.)

author: 9aplus
author_rank: Regular Contributor
timestamp: January 02, 2019, 07:14:15 pm
content: Here is my version of bicone...https://hackaday.io/project/28119-biconical-dipole-antenna-ikea-cones

author: ahbushnell
author_rank: Frequent Contributor
timestamp: January 03, 2019, 01:25:41 am
content: Quote from: 9aplus on January 02, 2019, 07:14:15 pmUmmmm bi-sphere. Looks nice.