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Author Topic: Steel tube antenna building  (Read 887 times)

N0AKX

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Steel tube antenna building
« on: July 02, 2021, 10:53:28 AM »

I am trying to build a 15.75 in steel tube antenna in replace of my Wonderloop copper wire. I do not have the tools for it... Any ideas? Is this something I could do at Homedepot?

Cho
N0AKX
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W9IQ

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Re: Steel tube antenna building
« Reply #1 on: July 02, 2021, 11:28:10 AM »

You do not want to use steel in this application due to the high losses. Consider larger diameter copper tubing that you can easily form by hand - it has very low losses by comparison.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W1VT

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Re: Steel tube antenna building
« Reply #2 on: July 02, 2021, 11:53:48 AM »

Steel is hard to work with so I avoid machining it, except for drilling holes in antenna masts with cobalt drill bits.
Steel work hardens so if your drill bit doesn't cut into it, it will harden the steel and make it harder to drill with the proper drill bit.

Surplus Heliax or Hardline has a corrugated copper jacket that can be used for small loop antennas.
The foam dielectric is bonded tightly to the copper and reduces its scrap value.

Zak W1VT
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WB6BYU

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Re: Steel tube antenna building
« Reply #3 on: July 03, 2021, 01:23:20 PM »

The problem with steel and other magnetic materials is that the
hysteresis loss can be high:  every time the direction of the
RF current reverses, the steel remagnetizes in the opposite
direction, and that takes energy.

Non-magnetic stainless steel doesn't do that, but it isn't
as convenient to work with.

My suggestion would be to get a piece of aluminum flat stock,
drill the ends to fit on the terminals, then bend it into a loop.
Much easier to work with, and you can find it at Home Depot,
Lowe's, or many other hardware stores.

You can also use a piece of copper tubing bent into a circle,
which is easier than trying to solder straight pieces into an
octagon or square.

AH7I

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Re: Steel tube antenna building
« Reply #4 on: November 21, 2021, 01:59:14 PM »

I am trying to build a 15.75 in steel tube antenna in replace of my Wonderloop copper wire. I do not have the tools for it... Any ideas? Is this something I could do at Homedepot?

Cho
N0AKX

If you have a local company that makes those awnings you see at small shops and restaurants, they'll have a stock of Al tubing and a roller for bending radius. Go with the smaller mom and pop...brothers...etc. shop. They can cut and bend a loop in about 15 minutes. Also they buy a lot of Aluminum so your total cost will likely be less than if you bought the same piece of straight stock retail.

Most will be set up for TIG weld too if you need tabs welded on.

73, -bob ah7i
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KC2TRX

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Re: Steel tube antenna building
« Reply #5 on: December 01, 2021, 08:19:53 AM »

  A question about steel antennas:  why does MFJ make their vertical whip antennas out of steel, if there are so many (alleged) disadvantages in using that material? Is steel really inferior to copper or aluminum?
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W1VT

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Re: Steel tube antenna building
« Reply #6 on: December 01, 2021, 08:32:09 AM »

Whip antennas are made out of steel because mechanical ruggedness is more important than efficiency.
You do not want pieces of a mobile whip falling off an automobile.

The OP is building an antenna that ideally has very high circulating currents compared to a full size antenna. 
So even a small amount of loss becomes significant.  High circulating currents typically correspond to good efficiency when you are building small loop antennas.

Zak W1VT
« Last Edit: December 01, 2021, 08:35:50 AM by W1VT »
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KH6AQ

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Re: Steel tube antenna building
« Reply #7 on: December 02, 2021, 07:28:59 AM »

G4VIO wonder loop:  http://www.g4ilo.com/wonder-loop.html

The wonder loop uses 250cm of RG-213 coax which is equivalent to 0.4" copper tubing. The wonder loop radiation resistance and copper loss at 7MHz is 0.0019 ohms and 0.055 ohms. The radiation efficiency, neglecting other losses, is 3%. 0.0625" O.D. aluminum tubing has the same RF loss resistance. Entering the properties of "electrical" steel in EZNEC raises the loss resistance to several ohms. I would use 1/2" copper or aluminum tubing for this antenna.
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N6YWU

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Re: Steel tube antenna building
« Reply #8 on: December 02, 2021, 12:14:56 PM »

  A question about steel antennas:  why does MFJ make their vertical whip antennas out of steel, if there are so many (alleged) disadvantages in using that material? Is steel really inferior to copper or aluminum?

IIRC, according to a presentation at Pacificon by N6BT, replacing those steel whips with AL tubing measurably increases radiation efficiency. 
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