Question for mechanical engineers - Not gun-related
Posted: Wed Oct 26, 2016 4:29 pm
I and a friend are trying to start an Amateur Radio Club for youth. I have two repeaters (both 70cm band) and 100' of Andrews Heliax. We have struck out trying to get a good antenna location, so I'm going to talk to my fellow Board members at the club about putting up a mast/antenna. I want to copy something I've seen done that involves using steel box tubing. (It comes in 24' lengths rather than 20' for pipe.) Here's a video showing the design. https://www.youtube.com/watch?v=cY-7VgZNypk&t=5s
I would like to get at least 70' AGL and I'm thinking of three sections of steel, each just small enough to fit inside the larger one. The pieces would either be welded or bolted, preferably bolted.
This mast would be sandwiched between two pieces of either box tubing or angle iron each 24' tall. The center mast would pivot at a point close to the top of the supporting angle iron or box tubing. The lower section would be weighted to make it easy to raise and lower the mast. (Since this would be a mast rather than a tower, it couldn't be climbed for antenna work, so it must pivot.) The concrete base would be sized close to the base required for an equivalent length tower. (That information is available from tower manufacturers.)
Is there a formula or reference I could use to make sure I used sufficient overlap with the telescoping sections? Just guessing, I would assume a 2' overlap would be sufficient. That would result in a 68' mast, plus about 10' of antenna, if the lower section is bolted to a mounting plate rather than being put into the concrete base. (24+22+22) If I were to put a section in the base, it would give additional height (24' less the portion in the concrete.) Also, I need to determine what wall thickness would be required.
Any input would be greatly appreciated.
Chas.
I would like to get at least 70' AGL and I'm thinking of three sections of steel, each just small enough to fit inside the larger one. The pieces would either be welded or bolted, preferably bolted.
This mast would be sandwiched between two pieces of either box tubing or angle iron each 24' tall. The center mast would pivot at a point close to the top of the supporting angle iron or box tubing. The lower section would be weighted to make it easy to raise and lower the mast. (Since this would be a mast rather than a tower, it couldn't be climbed for antenna work, so it must pivot.) The concrete base would be sized close to the base required for an equivalent length tower. (That information is available from tower manufacturers.)
Is there a formula or reference I could use to make sure I used sufficient overlap with the telescoping sections? Just guessing, I would assume a 2' overlap would be sufficient. That would result in a 68' mast, plus about 10' of antenna, if the lower section is bolted to a mounting plate rather than being put into the concrete base. (24+22+22) If I were to put a section in the base, it would give additional height (24' less the portion in the concrete.) Also, I need to determine what wall thickness would be required.
Any input would be greatly appreciated.
Chas.