Construction info for 1/4 wave 160 mtr vertical??

[k4kyv]

Also, has anyone had to jack up the tower to replace the insulator?  It looks like the Rohn tower base section has holes that could allow a sturdy pipe to support jacking.

Tom, K1JJ recently mentioned jacking up a tower to add a base plate and pier pin.  Maybe he could describe how he did it.

Some larger towers with tapered base section have jacking ears. I don't know if the bolt holes in the bottom of the sections would support the weight of the entire tower without bending or tearing the metal.  Perhaps some kind of bracket system that would clamp onto the rungs of the tower with multiple  clamps on each leg might work.

In any case, one would need to be careful.  Hazardous job, both to the operator and the tower.  

[K5UJ]

Using a pipe through the tower to jack is a bad idea.  You need flat surfaces.  You don't want to find out you picked the wrong pipe the hard way, or have it roll off a jack.  The base has to be made to be jacked.  Consider small I beams, size depends on the tower.  Here's a link to a photo of some jack ears to give you an idea.  

http://www.fybush.com/Tower%20Site/030424/high-is-twrbase.jpg

This is the base of the WFAN/WCBS tower on High Is. in NYC--the two stations share the tower.  

Having written all that, consider that if you get a good base insulator, it will probably last longer than you.  A lot of stations on towers that date back to the 1930s are still on their original insulators.  

[k4kyv]

Some likely causes of base insulator failure: vandalism, accidental rifle bullet from a hunter, projectiles flung from a mowing machine, filling with water (blocked weep hole) followed by freezing.

WSM in Nashville and some other major stations built brick walls surrounding their base insulators to prevent them from being used for target practice.  WSM did theirs during WW2 when the station was used to transmit some kind of strategic data simulataneously with their broadcasts and they were concerned about enemy sabotage.

I have a spare base insulator, but have no idea how I would jack the tower to replace the original. I would probably construct some kind of elaborate jig for the purpose.  You would only need to jack the tower a few inches to clear the insulator and pier pin, but the scary part would be working near the elevated tower base while no insulator was in place.  I would probably cast some kind of reinforced concrete pillar to temporarily slip under the tower base just as the old insulator was removed, and slip it out as the new insulator was placed in position.  Something probably better left to a professional or at least supervised by one.

You wouldn't use just one jack, but three jacks supporting the base in a triangle, and in turn ease each jack up a little at a time.

I have heard of towers up to 150' or so being constructed on the ground and lifted into vertical position using a crane.  I suppose that wouldn't be a whole lot different from jacking up one from the bottom. I'm not sure how they would safely attach the cables from the crane to the tower, other than "very carefully".

[KM1H]

There is a 500' tower on the next hill over from me that was originally built for CH 50 and a FM station. As the tower grew more users the base sections started cracking.

I watched a crew raise the tower and replace two 20' sections, they said they do it all the time and made it look easy.

Carl

[k4kyv]

I can't imagine a tower that wouldn't have enough safety margin to withstand the extra load from antennas on top, if everything was constructed according to specifications .  I'd bet they far exceeded the recommended wind load. Did they add a bunch of solid parabolic dishes?  The base sections didn't fail due to the dead weight of the antennas or dishes,  but from the resultant downward vertical force transferred via the guy wires from the horizontal forces of the wind.

[K5UJ]

You gotta also consider the feedlines.  Get enough dishes, cell phone, broadcast, two way radio etc. up there and the feedline weight really adds up especially if it's a tall tower like the 500 footer Carl mentioned--pretty long runs and some of the feeds are big and heavy if waveguide or big heliax.   Further get a lot of feedlines and it affects the windload.  Up north you also got ice shields adding weight.  I have seen towers with so many feeds the tower looks like a black stack in the air.  Now, if they have to be painted, you gotta have the feeds in matching orange/white colored sleeves so they don't affect the tower visibility.

[KM1H]

There were no dishes, just another FM stick and several 20' 2 way sticks. If I remember the details the tower was Rohn 85 and already marginal at 500' with the original antennas on that hill. The site owner had been told that.

It doesnt take many 1 5/8" cables to add up the weight to more than the tower itself. Ive got a bunch of it out back and its a 2 man job just to roll 300-600' of the stuff.