DIY Discone Antenna

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nspace01

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I decided, instead of buying one, I am going to build one.......

I am a Licensed Ham, KD5TPY, in Arkansas, and have some knowledge of antenna construction. I went through the formulas and here is what I intend (I hope that a antenna expert will correct me if I miss something):

Cone Component:

Since this antenna will be used with a scanner and I have no real interest in frequencies below 136mhz and due to the length of the materials that I will make the cone radials - 48"x1/8"1/2" aluminum flat stock - each cone element will be 23" long - by the formulas, the lowest freq that the antenna will receive will be 127mhz.

The diameter of the base of the cone will also be 23", with 8 total cone radials.

I will attach each cone radial to a 3"diameter x 1/8" disc with two 1/8" aluminum pop rivets via a 1” flap on each radial. I will drill a 3/8” hole in the center of the disc. On the underside of this disc I will attach a PL-259 connector. The center connector will have a 1” X1/8” copper wire soldered, insulated from the cone plate via a 3/8” x 1/2” rubber grommet.

Next, there will be a 3”x1/4” plastic/phenolic insulation disc.

Disc Component:

The disc component of the antenna will consist of a 3” diameter x 1/8” aluminum disc with eight 7 1/2” x 1/8” x 1/2” aluminum flat stock radials attached to the disc with 1/8” pop rivets. The total final diameter of the Disc Component (as per the formulas) is 16”. The center conductor of the PL-259 will pass through a center hole in the disc and attached to the Disc Component via a 1/8” screw.

Finally, there will be another 3”x1/4” plastic/phenolic insulation disc.

The antenna will be held together with four 1/4” bolts passing through the top cone disc, the first insulator disc, the Disc Component and the top insulator disc, insulated from the Disc Component.

Questions for the experts:

Will the antenna work as commercially available Discone Antennas? Would the 1/2” flat stock work in the same way as aluminum rod?
 

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Should work well for your application, I would however re-think the pop rivet fasteners, wind would cause the rivets to slowly lose their grip and the elements would move slightly and create noise in the form of crackling when the wind blows, which it does in this part of the country. I would invest in some stainless steel fasteners, have fun!
 

Rt169Radio

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Post some pictures when your done,it would be cool to see how it turns out.
 

jackj

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I know this will increase the cost of the project but I think I would use stainless steel instead of aluminum. Aluminum oxidizes really fast and the aluminum/aluminum oxide junction behaves like a diode. Also I would use stainless steel screws, washers and nuts instead of pop rivets. As rfradioconsult pointed out, the pop rivets will loosen and break over time.

Good luck with it.
 

prcguy

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Ideally the top of the cone should come to a point or close to it if possible. The flat stock should be a little better than rods since the perfect Discone is made from a solid cone and disc and there is more surface area with the flat stock.

You might want to leave options for changing the spacing between disc and cone since that affects matching. You would build as described then vary the spacing for the best match.
prcguy
 

nspace01

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What would be the effect of mounting a inverted identical cone assembly to the top, attached to the ground, insulated from the disc. Would this give more signal, having more signal to the disc? Or is there a issue that I have overlooked?

Nspace01
KD5TPY

---------------------
PRO-96 (Sucks)
Home patrol-1
IC-R2
IC-R75
 

fxdscon

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Should work well for your application, I would however re-think the pop rivet fasteners, wind would cause the rivets to slowly lose their grip and the elements would move slightly and create noise in the form of crackling when the wind blows, which it does in this part of the country. I would invest in some stainless steel fasteners, have fun!

I also agree with the comment on the pop rivets... from first hand experience! They WILL eventually loosen, and cause intermittent contact issues.
 

prcguy

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It should cut the impedance in half and will probably cause other problems. This was probably explored at least once in the last 60 or so years since the Discone was introduced.
prcguy

What would be the effect of mounting a inverted identical cone assembly to the top, attached to the ground, insulated from the disc. Would this give more signal, having more signal to the disc? Or is there a issue that I have overlooked?

Nspace01
KD5TPY

---------------------
PRO-96 (Sucks)
Home patrol-1
IC-R2
IC-R75
 

jhooten

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What would be the effect of mounting a inverted identical cone assembly to the top, attached to the ground, insulated from the disc. Would this give more signal, having more signal to the disc? Or is there a issue that I have overlooked?

Nspace01
KD5TPY


---------------------
PRO-96 (Sucks)
Home patrol-1
IC-R2
IC-R75

That would no longer be a disc-cone and would be called a bi-conical. A different animal.
 

thomast77

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I have wanted to build one of these for some time. I just never got around to it. I was thinking about building mine for 144. If my calculations are correct that would mean a disc about 13.944" and a cone of 20.506". I am seriously thinking of building it out of solid sheet metal instead of rods. It would have more wind load but if it is mounted properly it should work. I would need to take it down if there are any Hurricanes.

I like the flat radial design you have come up with that should work nicely. one option could be to rivet it then take it to a welder to strengthen it up some. I would be interested in seeing pictures once you have finished it.
 

swboss

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PLEASE,,, How do you start a new thread ??? WOW! How tough can they make it ???

PLEASE,,, How do you start a new thread ??? WOW! How tough can they make it ??? Someone please direct me how to create a new thread post........

S~
 

nspace01

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A bi-discone or double discone antenna does not have a disc. One cone is attached to the coax sheild and the other cone is attached to the coax center conductor. It is usually mounted horizonally instead of vertically.

My idea is a top and bottem cone of equal size, both attached to the coax sheild. Beween the cones, a disc is attached to the coax center conductor. Both cones are insulated from the disc. The antenna will be mounted vertically.

I have Googled and Googled and cannot find any reference or research into this kind of antenna. Surely I am not the first to think of it......................

If the antenna "experts" in this forum all say this design will not work better than a clasic discone disign, I'll trash the idea and go with the classic design............
 

fxdscon

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PLEASE,,, How do you start a new thread ??? WOW! How tough can they make it ??? Someone please direct me how to create a new thread post........

S~
Seriously??, "How tough can they make it?"

Go to the forums home page, click on the forum you are interested in, and click the button at the top that says -- of all things -- "New Thread".

Nothing tough about it at all.

In fact, do the same thing you did to create the new thread you started here a couple of weeks ago:

http://forums.radioreference.com/sc...how-import-databese-using-freescan-2-1-a.html
 
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majoco

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IMHO the flat section ali for the elements will flap around in the breeze and ultimately break at the fixing point due to metal fatigue - I have had to replace three ground plane tube section elements on my discone. After consultation I found that a wooden dowel inside the element prevented the flexing and also made the fixing more secure by not being able to compress the tubing - my fixing was by 10/32 nuts and bolts into an ali casting for the centre boss. It was a commercial antenna locally produced but no longer made.

Cheers - Marty ZL2MC
 

prcguy

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I have several military ground plane antennas with flat stock radials similar to the proposed Discone and they have no stress problems. The problem could be the alloy used on your antenna was not appropriate for the job and/or diameter vs wall thickness was a bad choice.
prcguy





IMHO the flat section ali for the elements will flap around in the breeze and ultimately break at the fixing point due to metal fatigue - I have had to replace three ground plane tube section elements on my discone. After consultation I found that a wooden dowel inside the element prevented the flexing and also made the fixing more secure by not being able to compress the tubing - my fixing was by 10/32 nuts and bolts into an ali casting for the centre boss. It was a commercial antenna locally produced but no longer made.

Cheers - Marty ZL2MC
 
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