Why is copper tubing used to make high q antennas?


by baconman71
Tags: antennas, copper, tubing
baconman71
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#1
Sep3-12, 11:06 AM
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My question is just what the title says. Why is copper tubing used instead of normal wire or enameled wire to make antennas and coils at high frequencies? Does it offer less resistance than normal wire?
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rbj
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Sep3-12, 01:26 PM
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copper has higher conductivity than nearly any other metal than silver (and silver is only marginally better). at high frequencies, there is a lot of "skin effect" where the great majority of the current flows in the outside layer of the conductor and the internal part of the conductor has nearly no current.

but i always thought that these high-frequency antennas were made out of tubular aluminum, because Al is light and, in a tubular shape, it is strong, to stand up to wind, etc.

i don't think copper is used too much, simply because it tarnishes when exposed to air over long periods.
berkeman
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Sep3-12, 02:19 PM
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Quote Quote by baconman71 View Post
My question is just what the title says. Why is copper tubing used instead of normal wire or enameled wire to make antennas and coils at high frequencies? Does it offer less resistance than normal wire?
Tubing is mostly used for strength. Like rbj, I haven't seen much in the way of copper tubing used for antennas, except for J-Pole antennas where you need to weld two pieces of tubing together...

yungman
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#4
Sep3-12, 02:52 PM
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Why is copper tubing used to make high q antennas?


I don't think conductivity play much roll in this. Conductivity goes up, skin depth goes down. It all null out particularly the conductivity is not that big a difference between good conductors. Most common rod antenna like rabbit ear are not copper!!! Skin depth is:

[tex]δ_s=\frac 1 { \sqrt{\pi f \mu σ}}[/tex]
davenn
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Sep3-12, 06:43 PM
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Quote Quote by rbj View Post
......
i don't think copper is used too much, simply because it tarnishes when exposed to air over long periods.
and is substantially more expensive than aluminium!!

Berkeman, I do have one copper tube antenna, a 40m band magnetic loop :)


Dave
vk6kro
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Sep4-12, 09:16 PM
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Quote Quote by baconman71 View Post
My question is just what the title says. Why is copper tubing used instead of normal wire or enameled wire to make antennas and coils at high frequencies? Does it offer less resistance than normal wire?
Copper tubing is used instead of copper wire because it has a much lower resistance.

Because of skin effect, the resistance of the tubing or wire depends on the surface area of the conductor and tubing has a much greater surface area than wire, for the same length.

Copper is used instead of aluminum where a reliable electrical contact is needed. It can be easily soldered and connected to a feedline where copper conductors are also used.

Aluminum can be soldered with great difficulty and it corrodes rapidly, especially near the sea.
It is lighter and cheaper than copper, though, and is used for TV antennas where periodic replacement due to corrosion is acceptable.
yungman
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Sep4-12, 09:24 PM
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Quote Quote by vk6kro View Post
Copper tubing is used instead of copper wire because it has a much lower resistance.

Because of skin effect, the resistance of the tubing or wire depends on the surface area of the conductor and tubing has a much greater surface area than wire, for the same length.

Copper is used instead of aluminum where a reliable electrical contact is needed. It can be easily soldered and connected to a feedline where copper conductors are also used.

Aluminum can be soldered with great difficulty and it corrodes rapidly, especially near the sea.
It is lighter and cheaper than copper, though, and is used for TV antennas where periodic replacement due to corrosion is acceptable.
Agree, particular aluminum is next to impossible to solder. I was told that you have to scrape the surface under oil and solder under oil after scrapping the surface to prevent oxidation of the surface. Tube for the same weight has a lot more surface area than solid wire.


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