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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