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Scanner / Receiver Antennas For discussion of any type of receiving antenna used by a scanner or receiver base, mobile or handheld.

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Old 12-29-2004, 8:12 PM
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Default How to make homemade discone?

full wave 14.04 inch rods or use 14.5 down to 13.5

anyone have any plans how to build one?

or should I skip full wave and go for 3/4 or 5/8?

any input ?
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Old 12-29-2004, 8:15 PM
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I used to have plans years back for one that used an SO-239 socket (one that would go inside a radio) and 5 pieces of wire if you will. 1 went in the center lead of the backside of the SO-239 and the other 4 went in the 4 mounting holes for the socket assembly. . It was the 'poor-mans' discone antenna.

The plans might be on the Internet someplace.
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Old 12-29-2004, 8:55 PM
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Wouldn't that be a regular ground plane antenna?

Mike
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Old 12-29-2004, 9:23 PM
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Yes, that would be an ordinary ground plane.

The best article on discone design I know of is "Designing Discone Antennas" by J. J. Nail, Electronics August 1953.

The discone was invented way back in 1946.
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Old 12-30-2004, 2:23 AM
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I don't know if it's the best, but certainly an interesting article! Thanks for the info.

Mark S.
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Old 12-30-2004, 1:07 PM
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Thanks! I remember the first one from when it came out. I just couldn't remember where I saw it. Nine years ago, even my memory isn't that good!

Mark S.
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Old 12-30-2004, 5:27 PM
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You can also make a discone out of a chassis mount SO-239 or N connector and wire. This one has 4 cone and 4 disc elements and is just for photo
purposes. I didn't solder the 2 disc wires yet. Something like this probably
wouldn't last long outdoors.

Tom
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Old 12-30-2004, 8:22 PM
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Thanks all

I made one out of (beat this)

A platter out of a hard drive for the disk on top.

some sheet metal with 16 copper wires running down the outside of it for the cone.

An old fan stand for the base (it had plastic inserts inside the telescoping boom,

It works great (maybe a bit too good, now I am getting a second MOT on the same frequency as one I already have)
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Old 12-30-2004, 8:39 PM
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Quote:
Originally Posted by nd5y
You can also make a discone out of a chassis mount SO-239 or N connector and wire. This one has 4 cone and 4 disc elements and is just for photo purposes. I didn't solder the 2 disc wires yet. Something like this probably wouldn't last long outdoors.
Tom
Umm, Tom, the problem with your design is that you cannot make a discone with 4 wires as the skirt. I mean it isn't practical. Ideally the skirt (the cone) of the antenna is solid, but if made from a cage of wires the bottom separation between elements should be no more that 0.02 of a wavelength. If you were building a 2-meter version, then the skirt elements would have to be a little longer than 19 inches and the bottom spacing between elements could only be about 1.5 inches.
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Old 12-30-2004, 8:53 PM
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Hustler sold a discone with three top elements and four for the cone. But you are right, with so few elements the losses are high and the antenna is very inefficient.
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Old 12-30-2004, 9:05 PM
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Lou, several years back I made a few of these cut for 118 MHz at the low end.
They had relatively low SWR on the 2m, 220, and 440 ham bands.
4 elements seemed to be just as good (or bad) as the RS discone
and a "solid" one made from 1/4 inch mesh. I don't remember if I ever
tried adjusting the spacing between the disc & cone apex.
I did make a flat one with only 2 disc & 2 cone elements and it didn't work.

Tom
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Old 12-31-2004, 1:49 PM
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I have a question, I looked at ND5Y's picture of the home made
discone and something is boggling the mind.
My understanding of discone antennas has the cone hooked to
the center conductor of the coax and the disc hooked to the shield.
While I think ND5Y's idea is neat, would it make a difference being
that it is reversed from what I have know as discone antenna's?

If I am wrong in my inderstanding of the construction, then I
apologize to all.
Thank in advance...
Danny
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Old 12-31-2004, 2:31 PM
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I think you have it backward
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Old 12-31-2004, 2:48 PM
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n4yek, you indeed have it backwards. And I guess by strict definition, that still is not a discone. More like a wide band ground plane. I would be interested to see if anyone has done antenna field strenth plotting on that design.
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Old 12-31-2004, 3:16 PM
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Here is a picture of my (experiment) it is a rough job made out of what I had in my shed.
The tape on the top was holding the copper wires in place until I could clamp them all down.

I will be making one out of copper this weekend.

Dont laugh
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Old 12-31-2004, 3:40 PM
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Merlin,

I am not laughing, but I have a question. Is the cone support you have there metal. If so, you don't need the wires.
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Old 12-31-2004, 3:47 PM
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Yes it is, but I was not sure how well sheet metal vrs copper would work.
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Old 12-31-2004, 3:50 PM
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I do have a question, does the cone act as a reflector ?

I am new to building antennas of this type ...
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Old 12-31-2004, 4:42 PM
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Quote:
Originally Posted by merlin-7
I do have a question, does the cone act as a reflector ?
Not a reflector per se. Let me quote the ARRL Antenna Book on the subject:
The radiation from the discone can be viewed in this somewhat oversimplified way. A traveling wave, excited by the antenna input between the apex of the cone and the disc, travels over the surface of the cone toward the base until it reaches a distance along the slant surface of the cone where the veritcle dimension between that point and the disc is a quarter wavelentgh. The wave field therefore sees a resonant situation and is almost entirely radiated. (pg. 7-18, ARRL Antenna Book, 17th edition)

While looking for the above explanation, I ran across another interesting point. It was noted that as the frequency gets higher than 3:1 or 4:1 from the design frequency, the angle of radiation begins to rise. This may explain another reason they are utilized in aviation. If the low end frequency cut-off was desgined for 40MHz, by the time it got to the aircraft band, it would start to radiate upward. I don't have measurements from the ones at airports but from just memory, it doesn't seem that they were as big as my discone on the roof which has a 50Mhz low cut-off.
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