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Old 18-Jan-2010, 10:26 PM   #22
Join Date: Dec 2009
Posts: 632
Originally Posted by herplace View Post
Would there be a good antenna building guide you could recommend or a place to start with theory etc?
The most common DIY antenna is a copy of a 4 bay bowtie antenna. This is good for UHF only, but it's easy to build and works pretty well. It is often referred to as the youtube antenna, although the same design has been copied in many places.

There is also the Gray-Hoverman family of antennas that have been optimized for high performance. They all support UHF. Some variants support high VHF stations. I'm not sure if they've come up with any for low VHF. These antennas are a bit more complex to build (nothing that a handy person couldn't handle), but their raw performance is better.

If you really want to get down to history and theory of antennas, then you can check out book resources like the ARRL Handbook and antenna analysis software like 4nec2 or ez-nec.

Do you happen to know if the aluminum used in the typical rooftop antenna has a particular quality. It's not especially strong it seems to me. I surmise that there are cost effective reasons aluminum is what one always sees. Does aluminum have some property that lends itself to antenna fabrication beyond lightweight rigidity? In terms of reception is there anything better?
Antenna performance is dependent on the electrical conductivity of all the parts. I wouldn't say that there's anything particularly special about the aluminum (or any other conductive material) used in antennas, but there are a few overall things to consider:

1) Beware of oxidation or other deterioration related to outdoor exposure. Some plastics are sensitive to UV, rust can cause some connections to stop conducting, temperature expansion/contraction might cause some parts to break or become loose, etc. Try to use materials and construction techniques that will stand the test of time.

2) If using mixed metals, beware of galvanic reactions. This can cause dissimilar metals to corrode if they are in close proximity to each other.

3) For longer (especially VHF-size) antenna elements, it's a good idea to use structures that can hold their shape well. The reason antenna "tubes" are used so often is because they are more rigid than a simple wires that might bend under their own weight. The mechanical properties of the materials you use will determine what kinds of steps you should take to have a structure that will hold its shape well over time and will resist some buffeting around by wind, snow/ice, and bird landings.

I'm full of questions.
Good. A healthy discussion is a great way to share knowledge/experience. For everyone one person that actually participates in the discussion, there are probably 50 others who will passively learn from it.

Is the thickness and hollowness of the long VHF elements, the specific shape of the ends formed during fabrication essential to gathering signal.
This should have minimal impact. Most electrical flow takes place on the outer "skin" of the antenna elements, so the hollowness of the interior has very little impact. The shape at the ends of the tubes is usually too small to have any impact because it is tiny relative to the wavelengths being considered (upper UHF wavelengths are about 15 inches). For the most part, antenna elements could be treated as wires and yield virtually the same results.

However, the angles and spacing between the conductive elements does matter. Connection points, the length of the elements, their relative positions/angles/direction, and the amount of space between elements are all very important in determining antenna performance.

I probably should just try to read up on this and not pester the forum with my curiosity but it would help to know as I get started.
No problem at all. This forum is all about OTA reception, and antennas (even DIY versions) are an integral part of that discussion.
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