vhf copper tube dipole antenna

[wqzw301]

I recently came across a 36" - 3/4" od 5/8" id copper tube, 101 alloy...
I am surrounded by the ocean, so I was thinking perfect length for a marine band dipole to place on my mast.
A nice wide band, low noise floor, antenna, to listen to all the boat traffic from Hudson canyon to NY harbor. Transmit also, And a chance to build my own antenna.
I know there is nothing compared to free space, but I would like to have as little loss as possible. Maybe some day use it with my icom busisness band repeater.
Instead of mounting the elements inside pvc nipple, electrical junction boxes, etc... (that can be found in plans all over the internet....) I was thinking of mounting the elements with a piece of 5/8" od fiberglass (inside the tube) and run an perpendicular 18" fiberglass pole back to the mast with feed line and quarte wave matching stub.
No fiberglass over any part of the elements but inside with a little jb weld and soldered feed line to the elements. Bare Copper Antenna.
Given skin effect, on the outside radiating part of the tube. Would fiberglass inside of copper tubing effect the impedance at all or (at the least) less than having the element emerge from a pvc conduit connector or plastic, making contact with the outside radiating part if the element.
My feed line will be a 20' piece of messi broad 10 solid copper with copper foil and copper braid I had left over from my uhf antenna.
Any Thoughts?
thanks ,
d

 

[prcguy]

Go to post #5 in the thread below and download the instructions. This will show you a great way to mount copper elements in a PVC pipe Tee at the feedpoint with accompanying arm to hold it out from a mast. There is also some info on the length of copper tubing for frequency range near the marine band. I would also put three snap on ferrite beads at the feedpoint and a #43 mix ferrite is good for VHF. This will help decouple the coax shield from the dipole.

You should not need any matching like a 1/4 wave stub and with 18" spacing out from the mast you will get an odd directional pattern with probably four lobes and a slight null in the direction of the boom pole. You would have to get a dipole at VHF at a good 6ft or more out from a mast to reduce interaction and directionality and even at 6ft you will not have a great omni pattern. I would recommend painting the copper and other parts to protect from the weather.

4-bay VHF dipole array project

This project was inspired by someone wanting a better antenna for VHF RR and this is about the best you can get. It will cover 2m through RR and can be custom tweaked if you have an antenna analyzer. The pdf instructions are a first draft, but it took longer to document the project than it did...

forums.radioreference.com

 

[jaspence]

Another good antenna often made from copper pipe is a j-pole. I used one for years with good results and no worries about structure stability.

 

[Ubbe]

/Ubbe

 

[iMONITOR]

Any copper exposed to salt water or salt air will turn green and corrode badly in a short period of time. Consider stainless steel.

 

[wqzw301]

/Ubbe

I'm not familiar with antenna modeling software
Is this the distance from the mast to the dipole?
My mast is fiberglass... Does that make a difference?
Thanks
d

 

[Ubbe]

My mast is fiberglass... Does that make a difference?

Very much so. It needs to be metal to change the pattern. Fiberglass makes it have a circular pattern. If you have a metal pole or sheet metal at those distances you will increase the gain in some directions and reduce gain in others, depending of what you prefer. If you reduce gain by 3dB in one direction it will add 3dB in the other.

/Ubbe

 

[prcguy]

Stainless steel is a poor conductor for antennas and has measurable loss. There was a website where some engineers made identical J-poles out of aluminum, copper and stainless then put them on an antenna range. The stainless versions were about 1dB down from the copper and aluminum versions with very little difference between copper and aluminum. You can prime and paint the copper and keep the good conductivity and it will last for years. I have a version of my 4-bay dipole project from around 2008 painted with Rustoleum and its doing fine today about a mile from the ocean.

Copper actually does really well if left alone. It will get a crust of green oxide then that will protect it for many years. In some parts of the country copper rain gutters are still in use after 100+yrs and they are still fine.

Any copper exposed to salt water or salt air will turn green and corrode badly in a short period of time. Consider stainless steel.

 

[iMONITOR]

Stainless steel is a poor conductor for antennas and has measurable loss.

That's odd, the Diamond D130J discone antenna that everyone raves about is made of stainless steel elements.

 

[prcguy]

Make the identical antenna out of aluminum and it will work a tiny bit better. Definitely measurably better but maybe not noticeable for most people.

That's odd, the Diamond D130J discone antenna that everyone raves about it made of stainless steel elements.

 

[wtp]

make it out of the copper and keep it inside ??