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Thread: Antenna Base

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    Antenna Base

    My friend and customer Ray designed a base for a Ham radio antenna that will eventually be mounted on top of a school, which is the highest point in the area. I machined all of the components for the antenna base. The antenna will be used for a Ham radio repeater station. The school didn’t want him to drill holes through the membrane of the roof, so it has to rely on weight and a large base to keep it from tipping over in the wind. The first step was to face and cut the stock to length.

    1. Cutting Off Stock 1
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    2. Cutting Off Stock 2
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    The next step was to set it up on the Bridgeport to cut the slot. I removed the chuck from the lathe and clamped it to the Bridgeport. Then I used a center finder to find the center of the stock so that I could zero my digital read out.

    3. Finding Center
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    Next, I drilled the center hole undersize just to remove some stock. In hind sight I should have done this step while the base was still in the lathe. (It is easier to drill a hole with the 7-1/2 HP lathe as opposed to the 1 HP Bridgeport.

    4. Pilot Drilling Stock
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    5. Drilling Stock
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  3. #2
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    Re: Antenna Base

    The next step was to cut the slots. I used a 1” roughing end mill. The depth of cut per pass was .050” and the speed was 800 rpm. The roughing cutter is a six flute endmill. The finishing cutter is a four flute endmill.

    6. Roughing Cutter
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    7. Finishing Cutter
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    The last mill operation was to tap the four 5/16-18 UNC holes. I tap drilled the four holes deep enough to provide room for chips, so that I could use a spiral tipped endmill. I tapped ½ inch under the power of the Bridgeport then backed off to clear chips. I tapped the last ¼ inch by hand. I have some spiral fluted end mills, which would push three chip streams out of the hole, but the ones that I have aren’t designed for steel.

    8. Tapping four holes
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    The next step was to go back on the lathe to bore and counter bore the center hole. If I were smarter, I would have done this during the first lathe cutoff and facing operations.

    9. Boring Base
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    10. Counter Boring Hole
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    Re: Antenna Base

    11. Chamfering Bores
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    And here is the base all done with lathe and mill operations:

    12. Base All Done
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    The next step was to drill and countersink the legs followed by chamfering the end of the leg. My 45° chamfering end mill has enough flutes that I can cut a 3/8” chamfer in steel in one pass – very nice.

    13. Chamfering Leg 1
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    14. Chamfering Leg 2
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    I really like the M. A. Ford style of countersink because it cuts clean without chattering. They can also be used on a drill press, because they are self-centering.

    15. Countersinking legs
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    Re: Antenna Base

    16. Legs Done
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    I drilled the scrap piece left over from the base. I figured the antenna mast could use some additional mass to keep it from tipping over in the wind.

    17. Drilling the scrap as a counterweight
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    The next step was the mast. I added a cap to the top to keep it from filling with water and possibly freezing or corroding. The other side had a collar to trap the mast in the base and to prevent it from rotating relative to the base. (The scrap tubing was just to show you how the pieces fit together.)

    18. Making caps for the mast
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    19. Three mast pieces in exploded view
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    20. Three mast pieces together
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    Re: Antenna Base

    I welded the cap to the top and the collar piece to the other side.

    21. Cap welded to mast
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    22. Other end welded to mast and dressed
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    Next, I assembled the antenna mast components.

    23. Mass inserted into base
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    The collar on the other end of the shaft was .005” proud of the counter bore, so when the legs were bolted on, they would clamp the mast shaft to prevent it from rotating.

    24. Mast proud of base
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    25 Legs clamped to base
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    Re: Antenna Base

    And here is the antenna mast base all done. The counter weight, which is not shown, would slide on the mass and rest on the base to add additional weight to the base.

    26. Antenna Base All Done
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    -Don
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    Re: Antenna Base

    Nice write-up with lots of photos.
    Would they have allowed a flat base stuck down with roofing tar ?
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    Re: Antenna Base

    Quote Originally Posted by frieed View Post
    Nice write-up with lots of photos.
    Would they have allowed a flat base stuck down with roofing tar ?
    I don’t believe that they would accept the roofing tar solution. They are very protective of their roof membrane. If the glued down antenna base was removed for any reason, it could damage the roof.

    -Don

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    Re: Antenna Base

    Beautiful piece of engineering, great machining and even better description and pictures of the process.

    And totally overkill for the task at hand! (in my humble opinion! )

    How about some concrete filled buckets on top of those legs? That should add more than enough weight and stability to the base.

    Mikel

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    Re: Antenna Base

    It does seem like there would be easier ways of accomplishing
    the “no damage roof mount” task. Could even include some
    welding.Really nice job though.
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    Re: Antenna Base

    I would have copied this design or even just bought one of these from Rohn. Depending on the application they are from $150-$500

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    Re: Antenna Base

    Depending on the antenna they are using and how it attaches to your base, you may need to solder a ground wire to your legs to act as ground radials. Would greatly improve the antenna performance.
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    Re: Antenna Base

    That is a thing of beauty! I like to think that this creation is shown to the students, along with the pics and descriptions of how it came to be.

    Almost seems like the young figure everything magically comes in a box after picking a picture on the internet. Have to find that one or two that get the "hands on" bug to continue the tradition of self fabrication and problem solving.
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    Re: Antenna Base

    Quote Originally Posted by Louie1961 View Post
    I would have copied this design or even just bought one of these from Rohn. Depending on the application they are from $150-$500

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    I use these all the time for cameras and wireless internet equipment. They work great but I feel for a ham radio antenna They might not be the best item.
    If the women don't find you handsome, they should at least find you handy!

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    Re: Antenna Base

    Quote Originally Posted by wb4rt View Post
    Depending on the antenna they are using and how it attaches to your base, you may need to solder a ground wire to your legs to act as ground radials. Would greatly improve the antenna performance.

    Burt, its a 2 meter repeater they are setting up for. The antenna likely already includes the radials as part of the antenna.

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    Re: Antenna Base

    Quote Originally Posted by Kevin_Essiambre View Post
    I use these all the time for cameras and wireless internet equipment. They work great but I feel for a ham radio antenna They might not be the best item.

    Actually Rohn is famous for making professional and amateur radio towers. This is essentially designed for a ham radio antenna.
    Last edited by Louie1961; 2 Weeks Ago at 11:11 AM.

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    Re: Antenna Base

    Quote Originally Posted by Louie1961 View Post
    Actually Rohn is famous for making profession and amateur radio towers. This is essentially designed for a ham radio antenna.
    Goes to show how much I know about ham radio stuff.

    One of these days I'm going to look into getting my ham radio license.
    If the women don't find you handsome, they should at least find you handy!

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    Re: Antenna Base

    It's a fun hobby

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    Re: Antenna Base

    Quote Originally Posted by Mikel_24 View Post
    How about some concrete filled buckets on top of those legs? That should add more than enough weight and stability to the base.
    Mikel
    I agree it was a little overkill. He was planning on using sand bags, but it is the same idea.

    Quote Originally Posted by jpump5 View Post
    It does seem like there would be easier ways of accomplishing
    the “no damage roof mount” task. Could even include some
    welding. Really nice job though.
    I agree, but I had fun building the parts.

    Quote Originally Posted by Louie1961 View Post
    I would have copied this design or even just bought one of these from Rohn. Depending on the application they are from $150-$500

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    Ray's comment on your suggestion:

    "I guess I would have considered it if I knew about it. Maybe I should have looked more."

    Quote Originally Posted by Shootr View Post
    That is a thing of beauty! I like to think that this creation is shown to the students, along with the pics and descriptions of how it came to be.

    Almost seems like the young figure everything magically comes in a box after picking a picture on the internet. Have to find that one or two that get the "hands on" bug to continue the tradition of self fabrication and problem solving.
    Amen

    I sent Ray a link to this thread. Here is his comment.

    "Looks like you have a nice group of welding friends there."

    I do appreciate all of the comments that everyone made to this thread.

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    Re: Antenna Base

    Looks great.... I'm wondering if guy wires would accomplish more than extra weight on that roof. Anyplace to attach them without getting in trouble?
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    Re: Antenna Base

    Quote Originally Posted by Louie1961 View Post
    Burt, its a 2 meter repeater they are setting up for. The antenna likely already includes the radials as part of the antenna.
    Hey Louie. I didn’t see that it is for a 2 meter. In that case that base should be more than adequate, but if using a mobile whip they may still use the legs for ground radials. I’m sure they have a good ham setting it all up. Been a ham for 30 years but not too active lately. Lots of QSO’s going through internet these days. A 2 meter handie talkie can go around the world.
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    Re: Antenna Base

    Quote Originally Posted by Don52 View Post
    Ray's comment on your suggestion:

    "I guess I would have considered it if I knew about it. Maybe I should have looked more."
    Don, you should probably consider some diagonal supports from the legs to the center mast.

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    Re: Antenna Base

    Quote Originally Posted by Louie1961 View Post
    Don, you should probably consider some diagonal supports from the legs to the center mast.
    I was thinking the same thing.

    -Don
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    Re: Antenna Base

    Quote Originally Posted by Louie1961 View Post
    Burt, its a 2 meter repeater they are setting up for. The antenna likely already includes the radials as part of the antenna.
    Does that mean the antenna is two meters high? I guess it's a full wave antenna??? I don't know much about this kind of stuff.

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    Re: Antenna Base


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