For hams and other radio enthusiasts, the best part of the hobby is often designing antennas. Part black magic, part hard science, and part engineering, antenna design is an art. And while the expression of that art often ends up boiling down to pieces of wire cut to the correct length, some antennas have a little more going on in the aesthetics department.
Take the discone antenna, for example. Originally designed as a broadband antenna to sprout from aircraft fuselages, the discone has found a niche with public service radio listeners. But with a disk stuck to the top of a cone, the antennas have been a little hard to homebrew, at least until [ByTechLab] released this mostly 3D-printed discone. A quick look at the finished product, resembling a sweater drying rack more than a disc on top of a cone, reveals that the two shapes can be approximated by individual elements instead of solid surfaces. This is the way most practical discones are built, and [ByTechLab]’s Thingiverse page has the files needed to print the parts needed to properly orient the elements, which are just 6-mm aluminum rods. The printed hub pieces sandwich a copper plate to tie the elements together electrically while providing a feedpoint for the antenna as well as a sturdy place to mount it outdoors. This differs quite a bit from the last 3D-printed discone we featured, which used the solid geometry and was geared more for indoor use.
Interested in other antenna designs? Who can blame you? Check out the theory behind the Yagi-Uda beam antenna, or how to turn junk into a WiFi dish antenna.
[via RTL-SDR.com]
I have mixed feelings about discone antennas. I’ve read a lot of comments about them, stating that they’re not better than a random length of wire.
Does anybody have positive experiences?
It is definitely better than a random length of wire. Though it may not be as good as a length of wire specifically cut for a specific frequency.
The balanced version, the biconic, is used in all EMI test facilities.
The discone is a good option if you need a broadband, omnidirectional antenna. I’ve seen an HF one made from 60′ telephone poles, arranged in a circle, with a wire connecting the tops of the poles, and many, many wires connecting that top wire to a small plate near the ground, at the center of the circle of poles.
The advantage of the discone is its (relatively) constant impedance over a frequency decade.
Analysis of a UHF discone. It’s far from a flat match over a decade, but the 3:1 SWR points are a lot farther apart than a 1/4 wave dipole: https://www.fars.k6ya.org/docs/All_About_the_Discone_Antenna,_QEX,_Jan-Feb-2007.pdf
For VHF/UHF listening discones are fine.
And most also work for transmitting on hambands.
Low gain but wide band with reasonable match.
Random wires will present random impedance’s at the feed point depending on the frequency, a discone is far more constant.
“I’ve read a lot of comments about them, stating that they’re not better than a random length of wire.”
This is a bizarre statement. A quarter-wave monopole (or half-wave dipole) is just a totally different antenna than a discone. “Better” just depends on your use. Do you need a wide range of frequencies? Wide beam pattern? Good impedance match? It just depends.
You can imagine a dipole antenna “evolving” into a discone, too. First, imagine the wires in a dipole flaring open (into a cone, unsurprisingly), getting fatter the farther they get from the feed point. That widens their bandwidth, and gets you a bicone antenna.
Next, replace one of the dipole arms with a flat ground plane (so you’ve got a disk, and a cone). That steers the beam pattern downward. While you could obviously guess from looking at the antenna that the bicone’s radiation pattern is “up/down” symmetric (it can receive from 10 degrees above the horizon just as well as 10 degrees below the horizon), the discone’s obviously is not. If you haven’t seen the radar engineering handbook, you should: looking at the dipole going to the bicone to the discone really helps to illustrate what’s going on.
So from a bandwidth/beam pattern perspective, the discone is a wide-bandwidth dipole steered downwards. Obviously screwing with the antenna also alters its impedance too, so there are other effects going on as well.
It totally just depends on what you’re doing with it.
“I’ve read a lot of comments about them, stating that they’re not better than a random length of wire.”
Some people are just like that, incapable of compromise.
Of course a wideband antenna is going to perform inferior to a purpose made narrow band one. But, it also limits you to a narrow band! Every antenna is a compromise. That is the nature of things. Choose the compromise that best fits your purpose.
Back in the ’80s, when I was heavy into HAM Radio, I used a discone antennae. It worked quite well, compared to a 1/4 wave antennae. All subjective, I don’t think I used instruments to get an objective measurement.
subtitle: “Or: what you shouldn’t 3D print”
I’ve wondered if it would be possible to make an inflatable discone antenna using radio-transparent and aluminized plastic/fabric. The idea would be to inflate it with helium and float it on the end of the coax cable for an quick and high in-the-field antenna. The wind might be an issue though…
The weight of the coax might be an issue too.
I’ve seen where some claim an inverted discone reflector above the discone elements like as shown is really effective also as noted above. I don’t think a monopole is used in that type design. I use for listening in the ranges specified and have thought about making loading coiled type elements to go even lower in frequency for a more background scan antenna coupled with a yagi or more directional antenna.
From my readings, looks like the longwire antennas if say portable and used for multiple frequencies… are best to have colored zip ties marking the optimal wavelength antenna wire length matching to be deployed.
I also have an idea where we could take and at least if there is a monopole antenna on the top, place a fractal antenna I’d guess is called a “director element” over. I’m thinking this can be performed for each driving element also.
Basically, cover with a fractal antenna design tube with a foam spacer. I’ve watched this video and looks like significant improvement in performing I’d guess like a directing element passive sympathetic resonance effect: https://www.youtube.com/watch?v=QWd0nEXFnrE
Great idea for building also and thanks for sharing.
Good stuff!
While I’m not active I do hold a valid ham licence from 1990, and still have a Radio Shack discone mounted in my attic.
While indeed a compromise its wide bandwidth is what has made it useful in many projects over the years.
Does anyone have any thoughts on this antenna for helium mining.