Help build Discone Antenna 30-512MHz

[ateet101]

I am trying to build a discone antenna with a frequency range of 30-512MHz. Can someone point me in the right direction in how to build one with this bandwidth?

I was researching the internet and came across a few documents on technique used. All of these documents base the size according to the lowest frequency, but I also want to set the upper bound

These are the documents I found

https://26hs4316.wordpress.com/antenna-construction/discone-antennas/
UHF Discone Antenna
http://kd0cq.com/downloads/Antennas/discone.pdf

 

[prcguy]

A Discone has a rated band width of about 8:1 but after about 4X the lowest design frequency the pattern shifts up above the horizon and they don't work so well up there. For a 30Mhz low end a Discone will need a cone skirt about 8ft long and 8ft wide and its upper cutoff would be about 240Mhz but in reality it would degrade in the VHF hi band range.

You can use a large Discone for say 30MHz to 90MHz then a smaller one for 100 through 512Mhz and combine them with an off the shelf diplexer.

A Discone is also a PIA to build due to the mechanics but for lower frequencies you can use wires for the skirt and attach them to a hoop made of EMT pipe bent into a circle for the bottom of the skirt. The top of the skirt can be a small round piece of sheet metal a few inches across to attach the skirt wires then use a CB type SO-239 to 3/8-24 stud for the coax connection and center insulator. Use another round sheet metal piece on top of the stud mount to attach the top hat radials.

If the Discone cone and top hat are made to spec you then vary the distance between the top of the cone and the hat to get the best match.
prcguy

I am trying to build a discone antenna with a frequency range of 30-512MHz. Can someone point me in the right direction in how to build one with this bandwidth?

I was researching the internet and came across a few documents on technique used. All of these documents base the size according to the lowest frequency, but I also want to set the upper bound

These are the documents I found

https://26hs4316.wordpress.com/antenna-construction/discone-antennas/
UHF Discone Antenna
http://kd0cq.com/downloads/Antennas/discone.pdf

 

[ko6jw_2]

Commercial discone designs such as those made by Diamond claim to cover 25Mz to 1.2Ghz. These claims are not to be taken seriously. The 30-50Mhz coverage of these antennas is provided by a base loaded whip mounted above the disk and the skirt and which uses those structures as a ground plane. The actual discone portion works roughly from 100Mz to 1Ghz with varying degrees of success. They are unity gain at best. I use one because I can also transmit on several amateur bands with low SWR.

I live in an area where there is little activity above 460Mhz so the higher frequency response of the discone is not an issue.

I agree that using two separate antennas is a good solution.

I directionality is not a concern, you could look into log periodic antennas. This is another method of getting wideband response with some gain. However, they are unidirectional. You can always use a rotor.

 

[AC9BX]

The discone is remarkable, offering about 6 octaves range, maybe as much as 10 but that's really pressing your luck, as the others pointed out it has limitations. And since antennas get bigger as frequency goes down they become quite cumbersome. Two antennas is probably the best solution to cover an extremely wide range. Thus the loaded vertical whip on top that many commercial discones feature. I'd not make it larger than 6 feet. Such an antenna will work pretty well for most of the range you are looking for. I would make a smaller one to cover high bands better and perhaps use a vertical (or two - maybe loaded to shorten them) and combine them with a diplexer or triplexer (or as some call a duplexer)

The discone is a funny animal. It's a vertical polarized antenna. The lowest frequency is the hard part, it's big. That's why you don't see much documentation about the high end. However, once you get above the nominal range the pattern gets weird with a poor elevation angle and polarity begins to shift to horizontal. A great reason to use one for scanning is because it's pattern looks to the horizon in a narrow beam so it hears well at a distance and is less sensitive to nearer signals. I like biconical antennae which are similar to the discone. 3 octaves is easy, 4 is reasonable, more than that is useful, more than 8 is not practical.

~ HF discone ~

Also as pointed out the log-periodic is a great wideband antenna and a favorite of mine. They are directional but as such offer gain in the intended direction. They too can become quite large. They are seldom made with ideal parameters (maximum gain versus size) because the size gets too big. For higher frequencies it becomes easier to achieve.

 

[prcguy]

The pic in your post looks like the Titan Missile base in Tuscon, AZ. That one uses the metal hoop at the bottom to connect skirt wires.
prcguy

The discone is remarkable, offering about 6 octaves range, maybe as much as 10 but that's really pressing your luck, as the others pointed out it has limitations. And since antennas get bigger as frequency goes down they become quite cumbersome. Two antennas is probably the best solution to cover an extremely wide range. Thus the loaded vertical whip on top that many commercial discones feature. I'd not make it larger than 6 feet. Such an antenna will work pretty well for most of the range you are looking for. I would make a smaller one to cover high bands better and perhaps use a vertical (or two - maybe loaded to shorten them) and combine them with a diplexer or triplexer (or as some call a duplexer)

The discone is a funny animal. It's a vertical polarized antenna. The lowest frequency is the hard part, it's big. That's why you don't see much documentation about the high end. However, once you get above the nominal range the pattern gets weird with a poor elevation angle and polarity begins to shift to horizontal. A great reason to use one for scanning is because it's pattern looks to the horizon in a narrow beam so it hears well at a distance and is less sensitive to nearer signals. I like biconical antennae which are similar to the discone. 3 octaves is easy, 4 is reasonable, more than that is useful, more than 8 is not practical.

~ HF discone ~

Also as pointed out the log-periodic is a great wideband antenna and a favorite of mine. They are directional but as such offer gain in the intended direction. They too can become quite large. They are seldom made with ideal parameters (maximum gain versus size) because the size gets too big. For higher frequencies it becomes easier to achieve.

 

[vagrant]

The pic in your post looks like the Titan Missile base in Tuscon, AZ. That one uses the metal hoop at the bottom to connect skirt wires.
prcguy

I have made contact with at least a handful of different operators that were using that particular antenna at one time or another. If I was in the neighborhood, I would enjoy giving it a try. I would probably spend more time listening on various bands than actually transmitting. I believe a club local there also has an event once a year and puts it to use over a weekend.

It is my understanding that a vertical element would assist with the lower range, as can be observed on many discone antennas. Still, this particular discone in the photo proves otherwise, yet practicality always comes into play unless it is a government funded project.

 

[SpectrumAnalyzer]

Help Build A Discone Antenna 30-512 MHz

The plans, design, theory & application for your discone antenna project is all in here:

Amateur Radio Antenna Projects

For real world tips, hints & opinions for DIY success try these three awesome sites:

www.qsl.net

eHam.net Home - Amateur Radio (Ham Radio) Community Site

HAM RADIO - AMATEUR RADIO - HAM RADIO INFORMATION, LICENSE INFO!, PLANS - PROJECTS

Good luck in your endeavor & let us know what you decide & pictures please.

 

[Ubbe]

If someone comes to this page for reference you should know that some misinformation exists.

" it's pattern looks to the horizon in a narrow beam so it hears well at a distance and is less sensitive to nearer signals." ????? That's crazy talk. The RF signal doesn't work as a magic bullet and changes direction in mid air and jumps over objects in the beams direction.

"once you get above the nominal (frequency) range the pattern gets weird with a poor elevation angle"

Inside the discones frequency range it works great. Look at AORs diagram for the DA3200 discone:

It doesn't loose much gain in horisontal plane but gain more vertical, up in the air, at higher frequencies.
Also see the PDF diagrams for lower frequency discones that show the same thing, not much loss in horisontal plane but gain more in vertical plane with higher frequencies.

/Ubbe