The new antenna is up and fully operational.
The slowdown in the work I talked about yesterday all focused on a simple enough part of the tower build, the house bracket. Makers of consumer radio towers generally insist on a house bracket because it reduces the amount of torque applied at the base trying to collapse the tower. Virtually every TV antenna mast uses a house bracket so the simple ones are big box hardware store items. This one is more than a bit different and totally custom.
Back in '16 while I was working on replacing the rusting out pole, I made a fairly accurate model of the tower and antennas to help me nail down the geometry and treat it as mechanical design statics problem. Along the way, I made a model of the house bracket and how the tower is secured.
The view is as if you were on roof looking down onto the bracket, which is in white. The house is transparent but the side of the bracket facing the house mounts to the house eaves and is lag bolted into the roof trusses. All of that bracket is 1" angle iron, and those corners were welded for me by a friend long before I started doing any metal working as hobby (and I still don't have a welder). The red rectangle is a 2x4, split lengthwise, that clamps around the tower legs as you can see. The inner half (bracket side) of the 2x4 is held to the bracket with a pair of 5/16"-18 bolts through the vertical portion you can barely see, and the outer half clamps to the inner with a pair of lag bolts. I ordinarily make those from a chunk of pressure treated 2x4 but last time I used plain wood because I didn't have any PT on hand.
It's barely visible in this drawing, but the house bracket actually tilts down a few degrees because it's mounted to the house eaves. That means the left piece of is downhill and that piece of angle iron accumulates water. Water means rust and it was worse than expected. It was time to re-wire brush, and re-apply rust treating primer. I did that yesterday and painted over the black primer with the white trim paint today. While taking the 2x4 off yesterday, so I could wire brush and prime the outside face of that piece of angle iron, a piece broke off the 2x4. Which suddenly meant it was time to remake that, and I had no end of little problems making that piece. I should probably paint 2x4, too, although that's less urgent.
Pretty much all of the painting was done by 1 PM and I searched for anything else to redo while the antennas were accessible. Late in the day, it was time to crank the tower back up and make sure everything went together as it should. Happily, it did.
This is the house bracket assembled - the tower bears the "scars" of earlier trim paint. I should really clean that off, one of these days. It's just inconvenient enough to reach that I don't get to it.
Finally, I re-swept the antenna and the data was almost identical to what I got yesterday with it pointed up. After the test data looked good, I turned on the station and verified the radio was happy with it, and it was. It was almost ecstatic. For a radio.
Finally, the completed installation. The new antenna (Directive Systems Engineering DSEJX5-50) is the one at the top, the lower antenna is my HF log periodic (LPDA) array, a Tennadyne T6. The way that the two antennas are mounted on opposite sides of the vertical mast adds some oddness to this perspective, which is pretty odd anyway.
For some time, I've been pondering replacing that house bracket with one made from aluminum to avoid the rust. Eventually that rust I fight every couple of years is going to force my hand and that bracket will have to be remade. I've thought it would be be better to perhaps machine the interface so that I don't need the 2x4 clamp, something that could maybe slip over the bracket and the tower cross bar (visible just below the 2x4 in that middle picture) and not even require hardware. Maybe just held in place by gravity. And maybe that's hoping for too much. Either way, it's not something that needs to be done immediately and can be thought about. All my antenna projects tend to start with the phrase "when it cools off" - maybe it's a next year project.
Nice. I've always envied guys with towers. I lost that argument with Mrs. Freeholder before it ever started.
ReplyDeleteI've got my new vertical (Hustler 6BTV with a lot of DX Engineering addons) up and am testing now. I can finally reliably get to South America. Going north isn't looking so hot, however. East-west is still an open question, but east is looking favorable.
I think after a week or two, I'll know how I want to change the tune, and I'll add on the 12 and 17 meter kits. But unlike you, I may be waiting for it to warm up.
Obviously, I have no idea where you are, the landscape around you, or anything like that. That said, the 6BTV antenna is a good design, going back to as far back in radio as I can remember as the 5BTV.
DeleteAs I was saying in the first post on directional antennas, a rule of thumb is that antennas work better high and in the clear, and more metal is better - if it's the right size and in the right place. If you have to keep an antenna in the attic, it will work better if you can raise it the couple of feet to put it right above your roof. Oh, and you can drop the part about being "high" with a vertical. They work best over water.
But that's a guideline that doesn't mean something that isn't "optimum" won't get you tons of contacts.
Can you just make a new steel bracket with open side of the angle down?
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ReplyDelete[updated]
ReplyDeleteGeez, just drill four holes in the horizontal angle iron and put two U-bolts in them to hold the vertical pipes of the tower! A 2x4 of uncertain angle and distinctly uncredible rot resistance is the wrong solution here. Take a hammer and bend the top of the angle in a bit where the verticals go past to make it relatively parallel.
If you're worried about strong pinch forces at the joint, put a couple pieces of split rubber hose around the tower legs to absorb a little bit of motion and use bigger U-bolts.
You could put a piece of angle steel on the away-from-the-house side of the 2x4, and run through bolts from steel to steel, so that wood becomes just a spacer in compression. You could replace the wood with the recycled plastic lumber they make into park benches. Or U-bolts like Malatrope said but instead of rubber hose force spreaders use half-cylinders of pipe.
ReplyDeleteYou do realize that, with the salt in the air here in east Central Florida, aluminum will ALSO corrode over time. Have you considered stainless instead?
ReplyDeleteSure. I'm not at the point of actually buying materials, but I prefer anything that touches the tower to be 316. Yeah, it galls, but that's a minor consideration here and it's very good in the marine environment. The aluminum has held up very well, and I think not physically touching the angle iron has helped. I check the tower regularly.
DeleteThe only metal that touches the tower has been the stainless cable to the winch and some stainless hose clamps. That has done well. I've used galvanized in some places - a couple of U-bolts to a bracket and the winch itself - and galvanized has acted like a sacrificial anode.
Malatrope and Anon 0224:
ReplyDeleteThere's a few things going on here.
In effort to keep this from being too a long post, I left out a lot of details that didn't seem part of today's story. When the system was first put together, this wasn't designed to the tenth of an inch. Even if it was, I wasn't good enough at construction to have built it to the tenth. I had a sketch of that bracket and my friend made it with what he had on hand.
When I put everything in place, the tower was so far from the bracket, it wouldn't touch. The 2x4 was a fix to get the bracket to reach the tower and get it to be useful. I originally intended to use U-bolts to hold the tower legs to the bracket.
In general, I'd guess I've replaced the 2x4 about every five years. Since hurricane Erin in 1994, I've had to take the antennas down for hurricanes every few years, and it always tends to be during one of those emergencies.
I'm more concerned about galvanic compatibility issues and longevity than the pinch forces. I had an aluminum boat that had some sort of electrolytic issues that led to holes forming in the hull. Every winch I've had, typically galvanized boat trailer winches, has rusted out within a few years. The one on there now needs to be replaced and is five years old.
I could use that recycled lumber for the 2x4 but I'd rather not need it. However, one strong point about the current installation is that I remove three fasteners, two on the bracket and one on the base, and can crank over the tower. I've prepared for a hurricane in less than half an hour.
I'll confess, not having lived in Florida since 1984 I completely forgot about galvanic corrosion. That said, I have another suggestion. Instead of wood, build a spacer out of a block of inch-thick plexiglass (teflon is nice, but it creep-deforms).
DeleteHere is a site that sells cast acrylic in whatever size you want. A 1.25" x 4" x 18" chunk is $38, but you could get two so you wouldn't have to rip it to go around the legs.
www(dot)professionalplastics(dot)com/PLEXIGLASS-ACRYLICSHEET-CAST
Oh, and Amazon carries stainless steel boat winches...
DeleteSix meters is starting to get interesting again. I've longed for - without success - a two band, 10m and 6m yagi. Three elements on each band would be just fine.
ReplyDeleteChris
I listened in on 10m within the last couple of weeks. Solar Flux was 130-ish and I know it supports transequatorial skip when it's in that range. There was some activity but not wall to wall. As we get farther into cycle 25, 10 will get more dependable.
DeleteMy first 6m antenna was that HF log periodic in the picture, operating on the third harmonic of something in its range. Worked well enough to get me started.