[Towertalk] Obssessive-compulsive Anal Paranoid Builds Over-engineered Roof-top Guy Anchors

[Jim Smith]

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