Mechanical fatigue; where the elements are formed this outer region is the thinnest as it is stretched the most in the forming process. Had this hole been drilled along the side it may have been a better choice as the thickness would be almost the same as the parent straight tubing however after this or any modification the material should be stress relieved as a precaution to prevent stress cracks from forming. This fatigue does not need to be induced by frost heaving but simple wind vibration may cause it to begin, having the screw go from the inside to the outside of the formed corner will help prevent the drilled hole on the thin (outside) side from opening outwards but the addition of a formed washer along the thin side will assist in keeping the material from opening over a wider footprint. I am thinking to try this without causing the mechanical stress drill across the outer curve and use thin bar stock twice the length needed with a insulating teflon or cpvc strap between the parallel sections a few inches from the end to secure the floating end and keep it from folding in the wind.
Laryn Lohman wrote: > > Derek, my concern is mechanical, rather than RF. > > Many moons ago, I received a brand new DB224 for the club, which was > soon to be installed at a new site. Observing the fine new aluminum > elements, I saw that the drain hole was not in the bottom of the > loop, but rather up an inch or two from the bottom. My infallible > wisdom dictated that a drain hole should be at the bottom. So, I > made it so. > > A year or two later we were getting a lot of noise on some signals on > the repeater. Inspection revealed that three of the four dipoles had > physically broken, you guessed where, right where I had drilled the > small drain holes. :( > > Having said all that, filling the hole with a good stainless bolt > like you did may prevent that kind of mechanical failure, I don't > know. There are apparently stresses and fatigue going on there that > I don't fully understand.... > > Laryn K8TVZ > > --- In [email protected], "Derek B. McIntyre" > <[EMAIL PROTECTED]> wrote: > > I have heard that adding whiskers to a DB-224 element > > > > Derek KC4FWC > > > > Yahoo! Groups Links > > To visit your group on the web, go to: > http://groups.yahoo.com/group/Repeater-Builder/ > > To unsubscribe from this group, send an email to: > [EMAIL PROTECTED] > > Your use of Yahoo! Groups is subject to: > http://docs.yahoo.com/info/terms/ -- 73...Clark Beckman N8PZD Pursuant to U.S. Code, title 47, Chapter 5, Subchapter II, �227, "Any and all nonsolicited commercial E-mail sent to this address is subject to a download and archival fee of $500.00 U.S.". E-mailing denotes acceptance of these terms. Yahoo! Groups Links To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ To unsubscribe from this group, send an email to: [EMAIL PROTECTED] Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
