Have You Thought of a Discone (
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- Опубликовано: 14 окт 2024
- Ivan, WC2S, Is building a simple ground plane antenna to try to receive some satellites. He has a lot of questions. "What is the effect of this vs leaving them straight out? Does it change the shape of the lobes, and if so, in what way? For reception only, will this matter? If both receive and transmit, is it the same answer?" Watch to learn more about what I think and what I suggest on his plan to reach his goal.
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Appreciate the video, Dave. I made a homebrew Discone years ago from a salvaged SO-239 connector, that was from the chassis of an old parts radio. The antenna worked pretty well, though the overall gain was fairly low. All in all, neat antenna project and nice bandwidth, too. 73, AC3HT
Ah, same could be done with any panel mount bulkhead. Good idea. There are plenty of ways to improve on that too. Im assuming your ground cone had 4 leads.
The LORA 433 Satellites are using LORA radios on the European ISM band. Tons of inexpensive antennas are available. Most of the satellites max out at about 30dbm so they are very low power, but LORA provides good weak signal propagation with a good deal of processing gain.
You're welcome Dave!!! Thank you for all your help! --- Nick S. W3NKS
You say in the video that noone really "knows" how a discone works - here's the best explanation I've found for it.
I didn't come up with this, and I can't find an attribution, but it makes perfect sense if you think about it.
Imagine a piece of coaxial feedline as a RF waveguide. That is essentially what it is at its core - electromagnetic waves travel down the cable through the dielectric due to potential differences and current flow on the conductors.
Now, imagine that you take the open end of that coax and turn it inside out, kind of like folding the top of a sock. Spread the outer shield into a cone shape, and warp the inner conductor into a disc. Depending on the angle, length, and spacing of the the cone/disc, you will have a certain impedance at the point where it folds, and a certain range of frequencies where it will work well. As you mentioned, you want the cone section to be at least 1/4 wavelength at your minimum operating frequency. So essentially what you have is a form of waveguide radiating a vertically polarized signal omnidirectionally.
Where this breaks down is when the cone and disc become very large in relation to wavelength - then it ends up acting more like a bunch of long wires and the radiation pattern starts looking funny. The commercial discone antennas tend to be designed with 100MHz as their lowest frequency, so they cover aviation frequencies and 2 meters well, as well as 220 MHz. Once you get to the 70cm band, the pattern is still "okay" and the SWR will remain low. But above that, they tend to throw a lot of energy vertically due to the "long" cone section. The low SWR continues up to around 10x the design frequency, but examination of the antenna pattern shows a mess at those high frequencies.
Your proposed design would likely work well on the 70cm, 33cm, and if built carefully, the 23cm bands. Possibly a very useful little antenna.
Thanks and 73 de N2NJZ.
That Ti Solar brings back memories.... Like early 80's memories. Was in band at the time and whoever sold the most candy bars won a Texas Instruments Solar calculator.. I don't remember the model number. Also, last time I was at the Smithsonian they had one on display :) cheers.
When I was a kid I made a 2 meter discone out of hardware cloth. I cut down a plastic cup to act as a spacer between the disc and the cone. It sat on my bed and worked great. 73 DE NØIP
I am in the United States and I thought the 70 cm band here was 430-450MHz. After a quick google, turns out I was north of a Line A this whole time. After all these years of being a ham and a couple more on top of it just listening, I learn something new today.
Interesting video David.
I made a ‘Tape Measure’ Discone just for RX purposes with parts of a tape measure for the disc on a SO239 like the one in the video. Then used copper audio speaker wire going down to a steel circle from a garden waste bag for the cone.
It works very well in the loft with my Scanner but doesn’t look too great! I may eventually invest in one off the shelf that is waterproof for outside.
Always fun to build and experiment. 73’s Franco 🙂
This just happened to be exactly what I was wondering about. Good information! Thanks Dave. 73, KF0GPX
Discones are pretty wideband, but suffer another problem: as frequency rises from the lower usable range, the radiation angle becomes strange - at a point where impedance is still good, the main lobe is well above the horizon. Great for talking to nearby aircraft ...
Thank you for sharing your knowledge, Dave. 73 Bret/AC0AE
There is a huge discone on the hills above Las Luz, New Mexico. I often wanted to stop in and talk with the ham that owns.
by the way, can you explain the * velocity factor * of wire, aluminium and copper, etc, it is vital to have when building antennas
i bought one of them at a ham fest for fifteen dollars. it did not have the wire that was used for getting out that little wire cost me ten dollars. it was a beautiful antenna for two meters. all though i was only about ten to fifteen blocks to the repeater the little wire wad on top of the antenna was for getting out..
Now I have very little interest in trying to build one because most of my experiments with antennas haven't worked out but many years ago in the 90s I bought a radio shack discone for a scanner and I was shocked at how good it worked with my two meter rig... It works perfectly for 2 m and 70 cm and I'm still using it today
I always wondered in you can transmit from one of those "Scanner antennas". Can you transmit okay with it? If so, I may get one.
Don't give up on trying!!!
@@chrissewell1608 I ordered one yesterday. I don't know if it has a decent band width. Maybe it depends on the frequency or on the coax used? Idk..
I'm guessing that was the Hustler DCX, that I also purchased from Radio Shack for scanning in 1977 or so, and is still manufactured.
I used it for 2-meter transmit several times with good results as well.
This is awsome. Where on the internet can I get the discone directions?
Still running my old radio shack sputnik
Great Video!
Do these have any vertical antenna on the top? Or is it just a flat disc, and the cone below? And how well do they transmit?
I like these cause they're so goofy looking.
? is he going to use it for receiving only
Solid advice David ... as always! 73 - KF6IF
6.7 inches is around 155mm.
Would a log periodic work?
This is exactly what I was thinking. It would be nice to point at the satellite, too.
Thank you, Dave. N0QFT