Ham Radio Tower

[GaryM]

S Line is nice stuff. One of my friends is a Collins Collector. He has several nice units. He has one that was built in Iowa, as they all were, but he found it on a trip to Isreal. Bouhgt it and shipped it back. So the trip from iowa to Missouri was kind of round-a-bout.

[GaryM]

Pat,

I have several friend with GA aircraft. I'll check and see if they have a tensiometer for rigging control cables. But I suspect that if they do, it won't read high enough values. Plus GM doesn't give any spec. for tension. At least I didn't see it in the manual. The anchors are rated at 4K in normal soil. I had planned to tighten the turnbuckles snug, a nice scientific value I know. I guess that would be about 100 Lbs of so?

Re the bolts, I'm tempted to use hex head bolts in lieu of the carrage bolts. The carrage bolts have larger dia. heads, but a washer under the bolt head would be about the same. The larger head on the carrage bolt is wasted as the nut has a smaller head! The sections butt together at the joint. The splice plates mearly keep everything aligned. There is no provision to plumb each section. Just the whole assembly.

[Pat]

Gary, You are right, A/C control cable tension is not as much as most tower guys. You are more in the sailboat rigging domain. I'd suspect that there are fitup tollerances and that tower sections aren't super constrained as to precise positioning so you'd most likely be able to plumb each section and then tighten the bolts rather than just trust that everything would automatically self allign perfectly.

I'm sure you are aware of the importance of keeping the tower "in column" at all times when tightening the guys and to always tighten the guys from the bottom up and loosen from the top down.

I have added another room to the house, another computer room/office and now shack. I was going to add an office for my wife upstairs next to where the upstairs shop (metal columns and trusses) adjoins the stick built section. Then I got to thinking how hard getting coax out of "my" comp room office might be and how a little more space might be good so I became so generous... I gave her my nice main floor office/computer room and I'll take the one to be sited upstairs. Since I am the architect, I get to proportion the space between the library and my newly sited computer room/office/ham shack. The library didn't really need to be THAT BIG.

I'm thinking I might run around the steel building section with my wire feed welder and tack everything together to avoid having any poorly bonded (RF and electricalyy speaking) steel sections. I might need the steel trusses and steel columns as a counterpoise for a vertical or whatever ham purpose comes to mind. I wonder what the feed point impedance would be for a vertical with 12:12 pitch steel trusses as drooping radials?

If/when I get a tower (still looking for an old oil derick) I hope to remote the amp(s) for some bands to the tower and just have the exciter/xcvr in the shack. Who knows, with some of these modern rigs I might remote the rig and just have a control head in the shack for some bands.

I haven't searched there but BoatUS or someone similar might have a decent price on a simple tensiometer.

Give us another peek at the tower when it gets taller.

Oh yeah, if there is a question regarding contact area under the head of a hex substituted for a carriage, you could buy some aluminum angle, cut it in short pieces, drill holes in it, and use them as washers under the heads of the hex bolts. Plenty strong, as good or better than the carriage heads and way more convenient since you can use a ratchet, drill-driver, or air tool.

Pat

[GaryM]

Pat,

The splice plates that hold each section together can only be bolted up with the leg extrusions in contact with each other. the splice plates only keep the legs in line. The bolts are really in tension rather than shear. The Rohn towers I'm familar with have the bolts in shear. IE each section is supported but the bolts through the tubular legs. Now it's true that the tube from the lower section is swaged down to fit inside the upper tube, and the bolt holes are drilled such that the upper tube should be resting on the curve of the swaged section...

This tower is assembled on the ground, then walked up to the vertical. All 70' at once. I figure I can loop a rope around the top and use the tractor to pull it up once the ground crew runs out of lift.

The Rohn heavy duty towers have stamped steel legs held together with two 3/8" or 1/2" bolts at each joint. If both bolts fail the leg drops.

I think some of the Alpha amps are self tuning. Make sure you run a 220 line into the shack, and I guess out to the proposed tower site, so you'll have power for the amps.

[GaryM]

Saturday ten other hams and I erected the 70' tower. We had a good crew and I mostly had to answer questions and hand out tools. Two structural/mechanical engineers in the crew gave me peace of mind. I knew thay wouldn't let us get into dangerous areas.

The two previously erected 10' sections were laid flat and the other sections added for a total of 7 sections or 70'. We discovered that the manufacturer had misdrilled some of the holes for the crossmembers that support the tracks for the Voyager tram. We clamped and field drilled new holes as required.

The tracks were bolted on and the tram tested for free movement. Then the guy wire attachment points were added and the guys attached. Guys had previously been cut to length. Turnbuckles and anchoring clips were added to the earth anchors and cable clamps prepared.

We looped a good stout 150' rope to the tower at about 50' height. The other end was secured to the boxblade on the JD4100 hydro.

I had lifted the top of the tower with my FEL allowing supports to be placed underneath. They pushed the tower up to about a 20-25 degree angle with extension ladders and I started pulling with the tractor. By the way, a hydro drive is ideal for applying a slow steady pull. I wouldn't have wanted to be feathering a clutch!

The tower slowly started up towards vertical. One time we had to stop and support the tower with a lader as it was muddy and the tractor started to slide off line. I repositioned and we continued. I pulled it up almost to vertical, then stopped. One fellow then pulled it the last bit by tugging the rope by hand. We wanted to be sure I didn't pull it past vertical. That's a NO NO!

After it was vertical we installed the 12 base bolts and hooked up the guy wires. I need to find a transit or someting to ensure it's plumb. The bottom is as I checked with a level. But the top could be off a little.

No antennas yet. I want to wait and see if anyone complains about TVI. Then I can point out that there are no antennas or cable on the tower!

Here's a photo of the finished job.

[weedsportpete]

Congratulations on your major milestone.

I noticed you managed to get in another argument in on the 'hydro vs clutch' debate..

Eagerly awaiting your next installment.

[Pat]

Roger the TVI strategy! I had a neighbor who over a period of 3 years (he knew I was a ham) complained to me about TVI on his cable reception about 6-8 times. During that period I only used 2m and 450 in the car.

Glad it went smooth for you. I'm not too impressed with the number of OOPS the mfg has in their work. Is this the first one of these they ever sold?

Plumb?? Can you sight up the track? Is it straight? use a plumb bob down it in a low wind period. If you or someone would climb the tower you could drop a plumb line from the top to the ground. the tower sections are all the same size, yes? No taper? then a plumb line down from the travellor (gondola) should do the trick.

Pat

[GaryM]

Pat,

That's my next plan. Going to give the guy wires a chance to relax a while. Then will loosen the turnbuckles and take out some of the slack. I know that the cables will get a little loose over the next few weeks.

Visually the tower appears to have a little lean to the East. But the lower section is plumb, based on a level. But as it's on a slope the lean may be an optical illusion.

I wish I'd been smart enough to measure the length of the side arm I bolted on to hold center insulators. Then I could drop a plumb bob from there. But I wasn't bright enough to do so!

I am quite disapointed with their manufacturing quality. I'm not sure I'd buy another one from them.

[Pat]

Gary, I sort of deduced there were quality problems from your earlier comments. As regards optical illusions (delusions?), the floor of the room above our master suite was shot and reshot and shot again with a LASER. One of the GC partners couldn't believe it was level although it was nearly perfect. I came along and looked at it and it looked for all the world as if was bowl shaped with the two western corners way above the middle and the SW corner even higher than the other.

We discussed the fact that there was a strong illusion at work.

Like landing or taking off with mountains in the background. It makes the runway look tilted when in fact it might actually be tilted the opposite way (dangerous situation if you don't check the published info.)

[Pat]

Now that you have had time for a reasonable use test, what do you think of the tower from a performance standpoint? What is your final word on quality and fit?

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]