Wow, what a writeup.
I guess my only question would be, "Why are you using LMR400?" Are you,
ummm, going to rotate that stuff?
>From the "been there, done that school of hard knocks:" I wouldn't.
-WB2WIK/6
"If everything seems under control, you're just not going fast enough." -
Mario Andretti
> -----Original Message-----
> From: Jim Smith [SMTP:jimsmith@shaw.ca]
> Sent: Thursday, November 21, 2002 12:10 PM
> To: towertalk@contesting.com
> Subject: [Towertalk] Obssessive-compulsive Anal Paranoid Builds
> Over-engineered Roof-top Guy Anchors
>
> I often see suggestions on TT that hams typically over-engineer their
> antenna support installations. Fifty years ago I heard the definitive
> definition of engineer. It goes as follows, "An Engineer is someone who
> can do for 50 cents what any damn fool can do for a dollar."
>
> I've been working on improving my modest antenna installation in an
> attempt to break free of that 1,000-Qs-in-a-contest barrier. The plan
> is to increase the self-supported Rohn 25 height from 25 ft to 30 ft off
> the flat, 2nd story, roof, swap out the old TH3 for a C4-SXL, get rid of
> the 40m dipole, mount an old Hy-Gain 6 & 2m beam above the C4, swap out
> the old Ham-M for an Alfa-SPID and mount it near the bottom of the tower
> where I can get at it easily, add steadying guys to the Rohn to
> accomodate the increased wind load, swap out the 30 yr old RG8 runs with
> 9 runs of LMR-400 (there are a few spares here), mount an aluminum plate
> with terminal blocks for rotor or other control cables and 9 barrel
> connectors (where the coax comes out of the conduit at roof level) to
> which the LMR-400 runs will be connected (to make it quicker to
> troubleshoot swr problems in the middle of a contest) and mount a
> similar aluminum plate in the shack wall to terminate the other ends of
> the LMR-400 and control cables.
>
> Why add 5 ft to the tower? Because I have a 5 ft chunk of Rohn 25 lying
> on the roof. Why bother? Because, at this rather low height, I expect
> to pick up 1 dB or so at low angles. Who cares about 1 dB when a 3 dB
> difference is barely perceptible? Think threshold. Statistically, if
> you're below it, no Q. If you're above it, Q. 2 dB is, of course,
> better. I hope to get at least that additional dB out of the C4 (and,
> of course, a lot more on 40).
>
> Got the C4, got the Alfa-SPID, got the Phillystran and grips, got the
> 1000 ft of LMR-400, got a 4' by 4' sheet of 1/16" aluminum for the coax
> termination plates (with a lot left over . . . always wanted my own
> sheet of aluminum) and got a 12 ft length of 1/4" x 2" aluminum bar to
> make the guy anchor station at the top of the Rohn (only need 7 ft but
> now a bending error won't kill me). Haven't sorted out what I need for
> a mast yet.
>
> OK, the Philly is rated at 2100 lbs. So I need turnbuckles, guy
> attachment points, etc. rated for at least 2100 lbs if I want to match
> the Philly strength. I do want to be able to tell the neighbours that
> the system is designed such that the weakest point has a very large
> safety factor (these are steadying guys, remember) so I want the Philly
> to be the weakest link. The plan is to attach the guys to the 4 corners
> of the house. (A 3 point guy anchor system would make one of the
> anchors rather close to the tower.) The house has a flat roof covered
> in vinyl, i.e. a deck.
>
>
> Sales Pitch For Flat Roof Follows
>
> Next house you buy (with due regard to snow loading), get a flat roof
> one, get rid of the tar and gravel, put vinyl on it and punch a
> stairwell through the roof with suitable enclosure and door. You'll
> probaly have to beef up the joists as the roof rating will now need to
> be for a live load as opposed to a dead one (people dancing as opposed
> to snow lying on it). You will have to add a railing for safety
> (non-conductive unless you can work out a "stealth" design for it . .
> hmmm... some kind of Moxon, maybe). Great for antenna stuff. Sell to
> the XYL by saying it's great for entertainment (which it is). Buy a
> fancy patio table, chairs and umbrella, a small barbecue with 10 lb tank
> and a Rubbermaid storage shed to store the umbrella, barbecue and tank
> and put it all on the roof. An elevator would be nice (but I wasn't
> able to sell that part). So, you're assembling your latest experimental
> yagi on the roof and it gets dark and tomorrow you're flying to
> Dusseldorf on a 2 week business trip. No problem. You just leave
> everything where it lies, close the door and walk downstairs. Nobody
> runs over it with the lawnmower. The kids don't use the elements for
> pole vaulting (you did lock the door to the roof, didn't you?). Nobody
> complains that it is unsightly. When you come back you just pick up
> where you left off. In other words, what you get by doing this is an
> extra floor of the house that is entirely yours to do with what you will
> except that it has to be tidy for social occasions, and then only in the
> summer.
>
>
> Back to Antennas
>
> In my case, the added railing to keep folks from walking over the edge
> consists of standard 2x4 framing which was installed on top of the
> existing 6" or so high parapet wall and covered with 3/4" plywood which,
> in turn, was covered with 10" bevelled cedar siding on the inside and
> cedar shingles on the outside to match those on the existing Mansard
> roof. When standing on the roof it looks like a normal outside wall
> covered in cedar siding except that, being a railing, it is only 42"
> high. So, when I screw the eye bolt into a corner of this railing for
> the bottom end of a guy, what's really holding it, a bit of cedar and
> some, perhaps rotting, plywood and 2x4? Off comes the siding. Off
> comes the plywood. No rot and I now know how the corners are framed.
>
> I decide that I don't want to screw an eye bolt into the corner as:
>
> 1. the guy will terminate only 3 ft or so above the deck surface.
> Remember the summer time social occasions? Can you football enthusiasts
> spell "clothesline"?
>
> 2. I don't like the risk involved in depending on one threaded eye bolt
> in wood to carry an expensive load for a lot of years (expensive to put
> up - more expensive to pull out of the neighbour's roof if it comes
> down). Here, in the rain forest, stuff rots where you can't see it.
>
> I decide that I want the guys to terminate about 5 ft above the deck
> surface. I now visualize a length of 1-1/4" square tubing fastened to
> the corner with lag bolts. Near the top of the tubing is an an eye bolt
> about 5 ft off the deck to which the guy is fastened. (I know, I still
> have bolts screwed into wood but now there are several of them and, if
> one starts pulling out because of rot or whatever, it won't be
> catastrophic and it will be obvious with casual inspection.)
>
> There is a problem with this as there is a sheet metal cap covering the
> top of the railing which projects out from the corner an inch or so and
> would interfere with the tubing. (I know, it's conductive, but it was
> all done before I got back into ham radio. Maybe I could cut it into 11
> ft lengths and separate them with insulators. Maybe I could replace the
> whole thing with the plastic equivalent and accept the UV deterioration
> problem.) There is also a strip of flashing sticking out 2" about half
> way up the wall which keeps rain out of a ventilation strip which runs
> around the whole perimeter of the railing. One could cut the cap and
> flashing to accomodate the square tubing but, if it is wanted to restore
> things to how they were, the cap would probably have to be replaced
> around the entire perimeter of the house. The flashing would be less of
> a problem but would still involve removing and reinstalling a bunch of
> siding. Looking forward (well, ahead is probably the better term) to
> declining years, I devised a method of supporting the steel tubing away
> from the corner such that it can all be removed and made to look good
> with only about a half day's labour.
>
> The solution was to, at each corner, attach 2 lengths of 4x4 to the
> wall. One length fits in the space between the flashing and the cap.
> The other fits in the space between the flashing and the deck surface,
> stopping a couple of inches short of the deck. A 1-1/4 x 1-1/4" piece
> of each 4x4 is cut out at the corner to accomodate the steel tubing.
> So, once installed, the steel tubing is spaced 2-1/4" (3-1/2" minus
> 1-1/4") out from the walls, providing clearance for the cap and
> flashing. In the future, the tubing and 4x4s can be easily removed and
> the exposed space covered with strips of wood. In what follows, I will
> refer to these 4x4s as "guy anchor support blocks".
>
> The question now becomes, "How do I fasten these chunks of 4x4 to the
> corner framing?" The answer involved many lag bolts and many CAD
> drawings and much looking at Crosby 3/8" and 1/2" eye bolts, shackles
> and turnbuckles along with lagging and gluing many pieces of wood into
> the existing corner framing. The carpenter I hired to do the work drily
> suggested that the 40 lag bolts per corner in my original design might
> be too much weight for the building to sustain so I managed to cut it
> down to 28. Friends suggested that lag bolts need a certain amount of
> wood around them to function properly - some even making oblique
> references to swiss cheese.
>
> In what follows, I'm going to talk about the south-east corner as I
> think it will make things clearer (but nowhere near as clear as a couple
> of photos).
>
> So, the original corner framing consists of 3 2x4 studs arranged to
> provide something to nail to at both the inside and outside corners.
> This particular corner style has a 3-1/2" x 1-15/16" gap in it where
> there is no wood. We filled this gap by cutting a 2x4 stud the
> appropriate height and screwed (6 screws) and glued a piece of 3-1/2 x
> 3/8" plywood of the same height to it. This exactly filled the empty
> space. A plan view of the corner now looks like the corner is made of a
> 5-1/16" x 5-1/16" piece of wood with a 1-9/16 x 1/91/16" piece taken out
> of one (NW) corner (the aforementioned inside corner nailing area).
> When we put the gap filler in we put construction adhesive on all hidden
> surfaces, slid it into place and fastened it with 6 long screws through
> the existing corner framing. We then cut some 3-1/2" x 5/4" material
> and a 4x4 to the appropriate length. We covered all the hidden surfaces
> of the 5/4 and 4x4 with construction adhesive, placed the 5/4 against
> the north face of the corner, placed the 4x4 against it and fastened
> them to the corner framing with 6 3/8" lag bolts. In this way, we have
> extended the corner framing nailing area inside the east wall by 4-1/2"
> (3-1/2" plus 1"). Now we have something to which we can secure the guy
> anchor support blocks. We did the same to the west face of the corner
> to extend the corner framing nailing area inside the south wall by the
> same amount. (If you haven't been counting, we're up to 12 lag bolts.)
> All of this was somewhat complicated by the need to accomodate the 120V
> ac wiring running through the corner for the deck outlets and lighting.
> We also ran 8 3/8" lag bolts through the bottom 2x4s of the new railing
> framing into the top 2x4s of the original parapet wall to accomodate
> vertical forces, 4 on the east side and 4 on the south side. (20 lag
> bolts and counting.) This was all repeated at the other 3 corners.
>
> 3/4" plywood goes back on and is covered with building paper. Awright,
> we got stiff corners now. Don't have the 1-1/4" steel tubing yet so
> made some 4' lengths of 1-1/4 x 1-1/4" wood to simulate the steel
> tubing. Painted them with aluminum paint so neighbours would think they
> are galvanized steel. Wouldn't want them to remember the wood and
> subsequently think, "He's got that huge thing up there supported by 4
> flimsy wooden sticks." There are 8 3/8" lag bolts securing the (now
> wood, later steel) guy anchors and their supports to the 4x4 extensions
> to the corner framing nailing area. Could have used fewer had there
> been one guy anchor support block per corner instead of two. For each
> of the two support blocks in the SE corner there are 2 lag bolts through
> the steel tubing and support block into the east wall 4x4 and 2 into the
> south wall 4x4. (Brings total lag bolts per corner to 28)
>
> Earlier I mentioned CAD drawings. Why wouldn't sketches do? In a
> vertical distance of 42" we have 20 3/8" lag bolts plus the 12 screws
> for the 2x4 plus 3/8" plywood filler plus another 12 screws I haven't
> talked about because it would have turned an already murky description
> into impenetrable mud. An obvious requirement was that none of these
> screws/bolts could be allowed to interfere with any other. Thanks to
> CAD, they don't.
>
> Next the siding goes on, cut back a little to butt up against the
> support blocks.
>
> The other night I dreamt that a huge tornado had ripped the roof right
> off the house. When last seen the roof and railing were sailing through
> the air with tower proudly vertical and guys still attached. The
> LMR-400 was getting pretty thin, though.
>
> Hope this was of some interest.
>
> 73 de Jim Smith VE7FO
>
>
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