Pvc in the sun will it warp

[stryped]

I am building a 440 yagi. Thinking of using sch 40 for the boom. Will it warp in the hot sun of summer or over the years being outside in the weather?

[Matt]

Don't know about warp - but it will deteriorate. If you have to use plastic, I'd go ABS.

[RBM]

[Percival P. Cassidy]

I think the grey PVC electrical conduit is more sunlight resistant, but I don't know about its insulation properties at UHF.

Perce

On 01/18/05 04:54 pm [e-mail] tossed the following ingredients into the ever-growing pot of cybersoup:

[DN B]

Cant say for sure...but, i made a PVC umbrella stand out of 1" and use it every summer in direct sunlight ; has not bowed at all.

[Greg]

Use EMT, It isn't that much more money and a whole lot more rigid. PVC will sag, bend and wave in the wind.

[SJF]

W7CJK here. I've used sked 40 and lighter for a number of experimental antennas. Very convenient and cheap. It probably will be OK as to warp if it does not cantilever (project from a support) more than three feet. I built a double rhombic for 900 MHz with a twelve foot boom and used diagonal wire struts back to the mast to support the ends which were six feet out. It was up several years without incident before the experiment was terminated. Don't remember now but it may have been 1" sked 40. Most of my experiments used 3/4" stuff.

IMHO it's a good material for experimental use as most ham projects are. If you plan a rather permanent installation, metal gives more reliability.

[stryped]

I would love to use conduit but it is conductive and I cant figure out how to insulate the elements from it. I was thinking of running the elements straight through the pvc. ANy ideas?

[SJF]

The directors and reflectors do not need to be insulated from the boom. However, the exact length you need will vary depending on which way you go. The center of the driven element may or may not need to be insulated, depending on the type of feedpoint matching. I generally used gamma match so the center of the driven element did not need to be insulated. On the driven element, slight variations in design length can normally be corrected in the matching process.

If you're fairly new to this stuff and following someone else's design, I would follow the mechanical details as closely as possible. Minor changes can alter the resonant frequency of the directors and reflectors enough to seriously impair the directivity and gain.

[stryped]

design, I

I am new to this. SO you have a plan that uses a conductive boom?

[SJF]

Sorry, I don't. Suggest you check the ARRL handbooks (library?). Any departure from a specific design of a yagi generally requires considerable skill and some test equipment. Good luck.