[TowerTalk] [Bulk] Please critique my plan for installing this tower and lighting protection
Grant Saviers
grants2 at pacbell.net
Mon Apr 18 12:51:15 EDT 2016
Not much to "critique" - all hams should plan as thoroughly and
carefully for large towers. Comments in line..
On 4/18/2016 7:28 AM, Dick Blumenstein wrote:
> Hello tower and antenna gurus-
>
> I was hoping that some of you would critique my upcoming plans and
> also answer any questions I have to see if they can be improved.
> (Thank you in advance for spending the time wading through this
> detailed description!!)
>
> I'm a relatively new subscriber to this forum and definitely new to
> owning a tower. I've read (a couple of times) what appears to be an
> excellent book by Steve Morris (K7LXC) "Up The Tower" and am trying to
> install this correctly the first time.
>
> 1. Tower - The tower is a 20 year old used 73' US Tower (Model
> HDX-572) in fairly good condition. Before starting the installation,
> I will pull it apart, replace the pulley sheaves and wire ropes as
> well as wire brushing and spraying on a coat of high-zinc content cold
> galvanizing paint. (It has a prop pitch motor for a rotator).
If you are taking it apart, you might consider regalvanizing it. I did
that for 20 year old Rohn 65 and it cost $0.55 per pound of steel to
strip the old Zn and patina rust and hot dip galvanize. Some logistics
to do that, but you will have another 20+ year no maintenance life.
Once painted, regalvanizing requires removing all the paint since the
stripping and cleaning solutions don't remove paint. That is very
difficult on a lattice tower. Cold galvanizing paint in my experience
has poor film strength and of course you have a wear point in the tower
motion. I'm a fan of Rustoleum commercial products and they do make
high film strength primers for galvanized surfaces if you decide to paint.
>
> 2. Concrete base - The recommended hole in the ground for the concrete
> base is 5' x 5' x 8' deep. There are 6 @ 1" diameter A36 anchor bolts
> required in the drawings which are specified at 27" long each. A major
> bolt supplier wanted over $130 per bolt for them! Wow! After much
> reading, it appears that I can possibly substitute an anchor rod (36"
> long and threaded at each end) made to the ASTM F1554 Gr 55
> specification that is also "S1 Weldable". I plan on putting a heavy
> duty WELDABLE nut on the bottom of each rod and just tack weld the nut
> in one place on the bottom to secure each nut. The anchor rod is hot
> dipped galvanized all except for the bottom end which is threaded for
> the weldable nut and then is cold spray galvanized afterwards. The
> bolts are arranged in 3 pairs of two, so I plan on getting made 3@
> 1/4" thick A-36 steel plates (3" x 6") made to slip down over each
> pair of anchor bolts and sit above each pair of welded on nuts. This
> will properly space the bottom of each pair of "bolts" as well as
> providing more pull-out strength to each pair of "bolts". At this
> time, I see no other way of holding the anchor bolts in place while
> pouring concrete except to suspend the tower plate as high as I can
> over the hole so that I can have room to work and smooth out the
> concrete below it when the hole is filled. Only 6" of threaded rod
> sticks up above the top of the concrete, so it only gives me about 4"
> of working height under the suspended base plate to work the top of
> the concrete.
Use the forms for the exposed 4 - 6" of concrete to support 2x4s that
hold the base off the finish height of the concrete as high as possible
with one nut under the base on each bolt. A little grease on the
threads that will end up exposed will make it easier to remove concrete
on the threads for the final leveling of the base.
With the concrete properly vibrated when pouring, the bolts will not
pull out. So, I think the nuts + plates are "belt and suspenders" but
why not when so cheap. A small matter is the pouring drop is far enough
that it is recommend to fill with a pump to the bottom and track the
concrete level as filled. Again, maybe overkill for this foundation,
but if there is significant water in the hole, pump the concrete to
below the water to keep the concrete mix together. The water then will
float up to the top and out.
>
> 3. Rebar cage - There is a rebar cage surrounding the 6 anchor
> bolts. Any suggestions on how to hold the cage off the bottom of the
> hole and center it in the hole without having extra rebar hammered
> into the sides of the hole to hold it into position? I would assume
> that any rebar sticking out past the edges of the concrete into the
> soil might provide a path for moisture to intrude into the concrete,
> eventually corroding the steel. Also, should I spray some
> anti-corrosive paint on the rebar cage? (See next paragraph concerning
> a Ufer ground. I assume that a coating on the rebar cage would reduce
> its grounding effectiveness.)
Do not have rebar closer than 3" from the edge of the concrete.
Inspectors check for this since it will be a rust path to the whole
cage. The 3" plastic risers are the easiest way to space at the bottom
of the cage and can also be used on the sides if you pour carefully,
Use a lot of them since you may end up stepping on the cage at some point.
Use LOTS of wire ties TIGHT to hold it all together. K7LXC used
triangular runs of #4 on the sides of my cages to help keep the shape
square. For a 589 base the bolts can actually touch the rebar if you
can have the concrete form orientation and bolt orientation right
(depends on where you want the tower to lay down). It's unlikely your
inspector will complain about extra rebar. Have all the rebar parts cut
and bent for you. Don't mess with manual rebar benders.
>
> 4. Tower grounding - I've read about "Ufer" grounds and then wrote to
> US Tower to ask why the 6 anchor bolts were not connected in any way
> to the rebar cage surrounding the bolts? They wrote back recommending
> to NOT connect anything to the anchor bolts inside the concrete.
> Hence, I plan to somehow connect all the steel rebar cage around the
> anchor bolts to a copper strap and bring it to the surface of the
> concrete pad to then run copper strapping to the base of each tower
> leg. Each tower leg will then have a copper strap go out to some kind
> of an array of multiple ground rods. Not sure how many ground rods I
> should really put into an array off of each tower leg? I plan on
> silver soldering all ground connections using silver solder and MAPP
> gas. For instance, I may use a 2" wide solid copper strap from the
> Ufer ground penetrating the concrete base, past and connected to each
> tower leg and then on to the outlying ground rod array. Whenever the
> copper strap encounters a ground rod, a hole is drilled in the strap
> the size of the ground rod and silver soldered at the top of the
> ground rod to the copper strapping. I will use a stainless
> connector to connect each steel tower leg to the copper strapping.
> (Any idea where to get them?)
UST advice re connections makes no sense to me, but... As mentioned
mine touch due to the cage/bolt orientation. I would not use Cu strap
in/out of concrete as there can be a corrosion problem and it is thin.
Use #2 solid or stranded ground wire and put the 20' per code in the
concrete clamped (SS hose clamps should be ok) to both cages and a lug
to the steel plate at the bottom of the bolts. (that gets around any
bolt corrosion concern from UST). Then the bolts are solid electrical
connection of the tower to the Ufer.
While the Motorola handbook is the "bible" for lightning protection (and
about as long) the Andrew guide for me was the Aha explanation of the
principles.
http://www.timesmicrowave.com/documents/resources/protectbrochure.pdf
The base makes a terrific Ufer, but "lightning is an RF event". So a
ground rod field with buried radials is needed. From each leg run #2 to
3x 10' grounds rods spaced 15'. So 9 rods in about a 90' diameter
circle. If that geometry doesn't work, use more radials, shorter. Just
like radials for a vertical antenna. One time Cadwelds are about $12
each, so get the right size and conductor orientations from your local
electrical supply, much easier, better and more fun than silver solder
if you have any pyro genes . DX Engineering has them cheap. With 9
rods I also achieved the "5 ohm" ground resistance desired for towers,
but that will depend on your soils.
Any copper wires you connect to the tower legs should have a galvanic
isolation. KF7P has a full line of these, nicely made with stainless
steel isolation. DX Eng also I think.
>
> 5. In the ARRL ham radio book, it suggests to connect all the ground
> rod system arrays that are around the tower with a large copper wire
> loop and then take that ground line (at least 6 gauge or bigger) back
> to the house where it connects up to the power company's ground at the
> power entry into the house and also the antenna ground junction box
> just outside my shack wall.
Yes, upsize per current code to #2, which also makes a good "ground rod"
and drop it in the conduit trench before the conduit. Frozen ground is
a poor conductor, so go below your frost line for everything if practical.
>
> 6. Antennas- I plan on having 3 antennas. The tower came with a
> Hy-Gain LJ-205CA 20m 5-element yagi antenna that I will initially
> install and then possibly replace with a 3 element SteppIR yagi in the
> future. In the original tower setup there was a dipole with traps
> that well served the previous owner, hung off the tower top that
> covered 160 to 40m. I plan on keeping that. Furthermore, for local
> communication, I plan to put above the yagi, a new 17' 2m/70 vertical
> that also came with the tower. The previous owner did not use one,
> but I would like to install an NN4ZZ "TiltPlate" so that when I crank
> down and lower the antenna system to the ground I can maintain it
> parallel to the ground without using ladders.
I rent 40' boom lifts for maintaining/adding/fixing antennas on my two
HDX589s. 23' of stacked tower plus up to 17' of exposed mast. So think
about firm ground access if you want to go that way, but only rent 4wd
versions. I got a 90' 2wd one stuck. Safer, easier, and you can work
anywhere on any element. There are even towable ones for 35 to 40' you
can rent at some big box stores and rental yards, but they work only
when nearly perfectly level (automatic on some up to 5 deg ground slope).
I think a lot has been written about re-optimizing and strengthening the
20M long john. google for that. Boom length is "everything" so don't
expect a DB18e (although it is a great antenna) on an 19' boom and 3
elements to equal a 5L on a 34' boom. (which is short for 5L at 20m). I
have 5 over 5 20m on 48' booms and a 4L steppir 32' boom to compare
(very "not fair" 'tho).
>
> 7. Antenna and rotator control wires arriving at the tower- There are
> 4 cables arriving at the tower; 3 antenna coaxes and 1 rotator control
> cable. I plan to install a PVC box near the base of the tower into
> which all the cables are fed. Inside will be a copper plate onto
> which is attached a copper grounding strap from the grounding system
> mentioned in #4 above. Each antenna coax will terminate in a
> connector and go through a Polyphaser which is also grounded to the
> strapping. The output of each Polyphaser will be a coax line which
> then exits the PVC box and heads outside next to the tower to run up
> the side of the tower to the antennas. In addition, inside the box,
> will be a grounded Polyphaser IS-RCT Rotator Control Line Protector to
> help protect the prop pitch motor and its controller back in the shack.
Aluminum plates work just as well, are cheaper and easier to machine.
Buy a big box, like 18" square or larger, fiberglass or pvc.
>
> 8. Controlling the "floppy" antenna and control cables? - In the ARRL
> book, there was a picture of someone using a fishing net to let the
> coax and control lines coil into it when the tower was cranked down.
> Anyone have a better "looking" suggestion other than letting the wires
> sit on the ground? (I plan on physically being at the tower each time
> I raise or lower it.)
KF7P makes both ring and loop standoffs for US Towers. I couldn't make
the "self tailing" ones work so Chris and I worked out the dimensions
for the HDX589 loop versions and they work fine. I don't believe in
remote up/down so tail the cables as they come down and flake them into
a large figure 8 so there are no twists.
>
> 9. Antenna and rotator control wires leaving the shack- The antenna
> wires are direct buried between the shack and the tower. Is it OK to
> run the prop pitch controller cable right next to the antenna coaxes?
> The distance from the shack to the tower might be about 40-50 feet. I
> may possibly run them inside a drilled out pvc pipe for protection, or
> just dig a trench and use sand as a filler around the direct burial
> cables. Just outside of the wall of my shack will be another PVC box
> slipped over a ground rod embedded in the soil. Inside the box will be
> a copper plate assembly that is clamped onto the ground rod which also
> holds 3 more Polyphasers. The antenna coaxes from the tower will go
> through the Polyphasers before heading through the wall into my
> shack. A 3" wide copper strap will go from that copper plate inside
> the box, through the wall onto a large copper buss bar which serves as
> a ground for all my shack equipment. Do I also need to put another
> Polyphaser IS-RCT Rotator Control Line Protector, in this PVC box, too
> (I suspect so)?
NO holes in your conduit!!!! Use 3" sch 40 PVC with large radius sweeps
and two runs and you will be happier in the future when a change is
needed. One for coax and one for control lines and UF dropped into the
trench for AC power. IMO, the additional protectors at the shack entry
may help but with the tower so close, may just be more cost.
>
> 10. RF ground, too?- At my previous home, all I had were a bunch of
> parallel vertical antennas suspended from a tree. I previously had 2
> additional "RF grounds" (besides the regular ground rods) composed of
> drilled out copper pipe, each located diametrically opposite each
> other about 12 feet from the shack entrance ground rod and connected
> to that ground rod. Each copper pipe was filled with salt to increase
> its supposed effectiveness. Now that I am using a tower, do I still
> need salted "RF ground rods" outside the shack wall in addition to the
> regular ground rod?
With the tower 40 from the shack, the tower radials could be extended as
a single field to additional rods 5' from the foundation and the entry
box tied to those #2 ground wires. The Motorola guide specifies a
ground ring around the structure, nice if you can do this, especially if
it ties your power entry panel into the ground rod field. The "single
point ground" is a mythological beast for most residences, especially
with multiple buildings.
>
> 11. Lighting rod protection - In Steve Morris' book "Up The Tower", he
> suggests putting a lightning rod as the highest point above the
> antenna system. However, I don't see how to do that. Won't that
> effect the performance of the 2m/70 vertical right next to it?
I've read furious debates about "lightning rods" and various static
"dissipaters" pro and con. If your 17' vertical is higher why bother?
Grant KZ1W
> Any suggestions would be appreciated from hams who have gone through
> this before.
>
> Thank you so much, and 73.
>
> Dick, K0CAT
>
>
> E-Mail: rcblumen at centurylink.net
>
> //
>
>
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