Ham Radio Tower

[GaryM]

Pat,

Here we go! The Glen Martin tower is an aluminum construction, 70' in height. It has two levels of Kevlar guys and comes with earth augers for attaching the guys. The tower incoporates their Voyager system where the rotor and antennas can travel up and down one face of the tower on a set of tracks. The tower is triangular with an 18" face. No need to climb the tower. When you need to work on antennas, or going on vacation for a couple of weeks. just lower the tram to ground level and greatly reduce the wind load. OK, you need to droop the guys toward the tower if your antenna boom is more than a few feet long, but it's not hard to do.

It may not work as well as I anticipate, but should be a lot safer to work on. You can get more information here: http://www.glenmartin.com/catalog/page3.html

[Mike_Dumond]

Looks like a nice system, but drooping the guys to lower the antenna would make me nervous a bit. I think I'd have to see one in person before I was comfortable with it. With that said, I'm jealous [img]/forums/images/icons/grin.gif[/img]

73's WA1ZPD

[GaryM]

That's a point to consider. But, there are two levels of guys, and only two of the three guys at a level need to be drooped at a time. And they can be retensioned as soon as the boom has cleared them. So I figure most cases, they're loose for about 10 minutes or less. And I'm hoping to have the non-drooping guy facing the prevailing wind. I really like the idea of being able to work on antennas almost at ground level. A friend, K9SD, has two 120' guyed towers that have to be climbed for service.

A 70' non-guyed tower that's rated for the same load is almost double the cost. So if it doesn't work out I'll try something else.

[Pat]

Gary, How about an update on the tower situation? Around here one good reason to lower the tower is high wind. Since our weather is so very difficullt to predict (with any reasonable degree of reliability) you'd be needing to lower the tower during a fair wind event. As the direction isn't always stable it might make slacking the guys a nervous activity.

Still, more height for less bucks is attractive. How do crankups with guyed or unguyed upper sections compare? Tilt over towers might be great for verticals and VHF/UHF but a decent sized beam makes for using a really tall ladder to get to the "works" without smacking anything into the ground.

Hope springs eternal from the human breast... so I still hope to find an affordable oil derrick so I can have a stairway to the top and a couple observation platforms on the way up. I figure I could climb to the top, mark all the pieces and dissassemble it on the way down, haul it and reassemble from the ground up. I have a oxy-acetylene rig mounted to an old backpack frame for ease of dissassembly.

Pat

[GaryM]

Hi Pat.

I had a contractor install the 4x4x4 concrete foundation and base mount. And instead of trying to screw in the earth auger anchors for the guy wires he drilled a 2' dia. hole and set the anchors in concrete. I don't think they're going anywhere soon!

I started to join some tower sections last night while waiting for the satillite TV guy to show up, and fond that I had received the wrong length braces that jump the tower section joints. Called Glen Martin Engineering today and havn't heard back yet.

I did order and receive my 6M beam. It's a M2 6m5x model. 5 elements on an 18' boom. Our club has the same one and it works well.

For HF I'm considering a Force12 XR-5 or C3. The XR5 covers 10-12-15-17-20 meters with no tuner and elements for all 5 bands. The C3 covers the same bands with no elements for 12 and 17. Uses a tuner for those two. Performance is close, but I think I'd prefer the XR5.

Still need to pick out a 2M beam.

The GM 1870A is rated for 18 sq. ft. at 80 MPH. A lot of manufacturers rate their towers at 50 MPH. We know how realistic that is! I'll probably end up with about 14-15 sq. ft. of load, so should have some extra margin.

The guyed tower gives you more load for less money. The Voyager eliminates climbing so yeah it's a little trouble slacking the guys and cranking the tram down. But it's a lot less trouble than a fall off a 70' tower.

As you said, a crank down tower, or a crank down and tilt over, still require some climbing or a tall ladder.

[Pat]

Gary, It sounds like you'll be setup pretty well. I'm envious. You have chosen well, Grasshopper! All this tower and beam talk reminds me of the tower and beam on top of Point Loma in San Diego, CA. It was left over from what was previously NELC (Naval Electronics Laboratory Center). It survived several mergers and renames and is now a part of the SPAWAR SAN DIEGO complex (Space and Naval Warfare Research... or whatever) ANYWAY..

The beam is a HUGE HF log periodic. I don't know the actual tower height, just tall and very heavy duty. It has something like 13 elements or so. Its "keel" was a triangular tower looking assy run horizontal. I'm sure they biased it in manufacture so it was straight when horizontal and loaded. Its swing radius is like a baseball diamond. The lab's ham club had sometimes access to it. It got out just fine. Ahh, our tax dollars at work. I drove by it thousands of times and always dreamed of having something like it, impractical but oh well, we can dream.

If I don't find a used derrick that can have regular stairs, I'll settle for something I don't have to climb real high. I have climbed lots of towers, some way over 100 ft many times. It is not my favorite thing. Tilt overs with "real" beams require way tall ladders that are more dangerous than climbing the tower. At least with a crank up you can get within something like a section and a half of the ground which isn't so bad. Your solution, like most, is the combination of tradeoffs and compromises that you picked as suitable for you. I really like your solution but tend to prefer a crackup at this location (baring a derrick) because I can lower the tower for high wind situations. If maint were the only issue for me, you have found a near ideal solution. I have this, perhaps unrealistic, concern for high winds, living as we do only a few miles from ground zero of tornado alley.

If I can find an economical source of utility poles (I have a source of a $50/hr util pole setting truck with auger) I might experiment with rhombics and other layouts of skywire.

Uhhhh, those holes drilled into concrete in place of augers... what concrete?

Pat

[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.