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Build Your Own Antenna - Discuss topics for building your own antenna.

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Old 10-05-2017, 8:46 AM
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Default Antenna element materials/sizes

I've been researching antenna element materials for a bit for a few NOAA, satellite and base station builds recently. I was surprised to see how low aluminum was on the list of electrical connectivity list, and how high copper was rated. I've got access to a fair supply of copper tubing, of just about any size for wholesale prices, so I'm curious as to the dimensions of what it use and why.

I plan on using hard drawn copper, even though its slightly less sensitive (by a minuscule amount) than soft drawn. I just need it for its rigidity and durability. But what determines the diameter of the tubing for the elements? I can get 5/16" upwards of 3" hard drawn, so sizes aren't an issue. The majority of antenna plans say to use 3/4", but why, and of what type? Copper comes is a few classes, type K (thickest), type L, M, DWV... I'd imagine the diameter of the elements will also take into account the thickness of the tubing itself.

Here are some charts of copper types and thicknesses for anyone who can help.

https://www.petersenproducts.com/category-s/1979.htm
https://www.copper.org/applications/..._tube_tbl.html

I understand that the frequency will also dictate the characteristics of the elements, but smaller is preferable...less of an eye sore in the air lol. I plan on a few builds to cover NOAA, some weather satellites, railroads (similar to NOAA frequs.) and maybe general purpose mid range scanning (100-800mhz) and local law enforcement. Not all will be covered by one antenna, I plan on making specific task antennas. I've already built a general purpose dipole out of 3/4" copper hard drawn, and it works very well, but I wanted more.
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Old 10-05-2017, 9:28 AM
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Diameter has a small effect on resonant length. The thickness of the tubing doesn't matter much because the RF skin effect dictates that currents only flow in the outer surface of the conductor. Larger diameter increases the usable bandwith of the antenna slightly. 3/4" is recommended because it's commonly available and rigid enough to withstand high winds. If your plan specifies that size, then the lengths in the plan will be adjusted accordingly. If you use a different size, be prepared to trim the length a little differently to get the correct resonant frequency.
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Old 10-05-2017, 9:39 AM
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The larger the diameter of the element, (the main transmitting element of a yagi, etc.) will usually have a wider band width. Using the hard drawn copper is your best bet, it won't be that much in sensitive that you would be able to detect. Plus it will stand up better in the wind to a degree.
Aluminum is used because it is substantially cheaper than copper. But overall, it still makes good antenna material.
Makes my heart feel good to see people experiment and build their own antennas. You will learn a lot.
The one antenna that will be kind of hard to fabricate will be the weather satellite antennas; right turn, left turn, circular, etc. (I may be showing my lack of knowledge on that antenna system; never built one, seen 'em, that's all)
(after note: the tube types, "K", "L", "M", etc., can get you. There's a small difference in size.)
HTH

BTW, always make your antennas slightly longer than called for. For example, an element for 146 Mhz is 38.4657 inches long; make it 39 and trim down.
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Old 10-05-2017, 9:41 AM
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The element length will be determined by the desired resonate frequency. There are quite a few charts that will list length vs frequency and what the element is used for, reflector, director or driven element. The diameter will effect the bandwidth, larger diameter = broader bandwidth. Again, there are a lot of charts and tables that will assist you in designing your antenna. Wall thickness will not effect the antenna's performance, the signal only travels on the outside of the conductor, called skin effect.

But why reinvent the wheel? All that design work has already been done, just pick the type of antenna you want and build it using the materials you want. The actual performance difference between aluminum and copper elements will be very small.
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Old 10-05-2017, 12:26 PM
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So, basically I need to get an antenna analyzer is what people are subtly suggesting lol. I can do that

I was just curious as to why 3/4 was recommended a lot of the time, and if the thickness of the tubing had much if any effect. It sounds like 3/4" is best for wide band coverage, that I understand. Tube thickness and length are almost directly related (ticker tubing will affect length compared to thinner tubing), so an antenna analyzer is needed to be spot on frequency.

I will look for charts though, I love a good reference chart.
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Old 10-05-2017, 12:32 PM
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Not tube thickness, just the outer diameter.
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