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Cabling

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Cables between the Tower and Shack
 
The tower designed called for nearly 100 wires between the tower and shack. In addition to two hardline runs for the station's two radios, many control wires were required:
 
1   8-conductor rotor cable for 40-2CD Tailtwister
3   5-conductor rotor cables SteppIR TIC rings
3  16-conductor cables for 4-el SteppIRs
1   9-conductor cable for MicroHam Stack Switch
2   8-conductor cables for SO2R 2x6 switch
 
I ran spare cables for the Tailtwister, TIC rings, Stack Switch and SO2R switch, for a total of 14 control cables (I already had a spare 16-conductor SteppIR cable running from the tower site to the shack from the AB-577 installation.)
 
The distance between the tower and shack is about 225 feet. After much deliberation, I decided to direct-bury the cables. My other tower farm, which includes the 72' tubular crankup, two 50' AB-577s, a 40m 4-square, an 80m delta loop and a 160/80 trapped inverted vee is about 265 feet from the shack. When I installed that system nine years ago, I had a 4-foot deep trench dug and installed three runs of electrical-grade PVC conduit: 4", 2.5" and 1". This was necessary because the motor that raises the crankup requires AC, and local code requires the AC to be buried in conduit.
 
We ran into much ledge when digging that trench, increasing the cost of the job considerably. I had good reason to suspect that one or more seams of ledge lay between the new tower site and the shack, and wasn't in any mood to go through ledge busting again. I wasn't real excited about pulling 14 cables, especially through a conduit with a 90-degree turn. As you will see below, conduit wasn't feasible for the hardline.
 
 
1-5/8" Heliax on spools

heliax.jpg
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I couldn't find any 7/8" 50-ohm hardline for less than retail. I posted a WTB message on a couple of reflectors, and got a lead on some brand-new 1-5/8" heliax left over from a cell tower project. The price was $1/foot! I also found connectors at a reasonable price, and this heliax doesn't require a special prep tool.
 
The only problem is that the stuff is a bear to handle. It comes on wooden spools that are over 6' in diameter and must weight at least 300 lbs. The heliax itself weighs .8 lbs per foot. So, 200 feet of this stuff on the spool is going to be in the neighborhood of 500 lbs. You'd need a forklift and a flatbed truck to transport it.
 
For SO2R, I needed two runs of at least 220' each. We found one spool with about that much, and another with 350'. I may run the excess up the tower, or I might use it for another project. We uncoiled the heliax, then wound it up to about 4' in diameter so it would fit through the doors of a cargo van. It took three of us to do this, and a lot of muscle. Eventually, we refined our technique and it went more smoothly. Big job.
 
The heliax will be direct-buried in a shallow trench. No way I'm going to pull two runs of that stuff through conduit! Besides, when I put in conduit for the crankup we ran into a lot of ledge and it cost a small fortune to pound it out.
 
 
Many Cables

Many Cables
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Tucking two runs of 1-5/8" heliax and 14 control cables under the sod wasn't feasible or wise (think driving heavy equipment over the path in the future), so I hired a guy with a tractor-mounted Ditch Witch. Wonderful machine -- it can cut a much neater trench than a backhoe and can go 40" deep if necessary. I elected to go 18" deep, though I knew big rocks in the path would probably force the trench to be more shallow in some spots. As a bonus, the Ditch Witch could dig three 50' long 8" deep trenches for the ground rods and radials of the tower ground system.
 
First problem was locating the cable to my 10' satellite dish, which crosses the path of the new cable trench. I rented a metal detector, but it was useless. The trench guy had the solution: a professional cable detector. This is a two-piece unit, one piece of which puts a pulse on the cable, and the other piece of which is a portable wand to detect the signal. He found the satellite cable in seconds. I carefully excavated it, surprised to find it was only 6" deep instead of the 18" the satellite installation crew told me 13 years ago. Since it was so shallow, we had to thread all the new cables under it.
 
Unfortunately, I was too busy to get pictures of the Ditch Witch in action. This shot and those that follow were taken after the trench was dug, the cable was laid and the trench was backfilled. This is the termination at the house. The metal NEMA cabinet on the right is the termination for the cables from my crankup tower and five other antennas near it. Note the three runs of conduit. The shack ends of the two 1-5/8" heliax runs are lying on the ground, while the 14 control cables are draped over the utility box. I'll mount an identical NEMA box 32" to the left. It will contain lightning suppressors for all cables, which will then proceed through the back of the box between two studs in the basement ceiling, and thence up through the floor to the shack.
 
 
Leftover Heliax

1-5/8" Heliax
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Here's what was left of the larger coil of heliax after we laid the first run in the ditch. There should be at least 125 feet of heliax in that pile. Originally, I planned to use it for two runs up the tower to the stack switch. But after seeing how much space that would take on the tower, I opted for a couple of runs of 7/8" heliax. I'll use the leftover 1-5/8" heliax for runs to the 10m and 15m AB-577 towers in the other antenna farm.
 
Note the radial trench to the right and the guy anchor in the center distance.
 
 
Start of Trench

Start of Trench
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Here's a shot of the beginning of the trench. The plan is to connect the heliax runs directly to Polyphaser bulkhead coax lightning suppressors mounted in the bottom of the new NEMA box. The control cables will be brought up to the box through a short length of 4 conduit, possibly a 90-degree sweep. They'll connect to K5FD SP12 lightning suppressor boards mounted on the ground panel inside the box.
 
Backfilled Trench

Backfilled Trench
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This looks worse than it is. The trench itself is less than a foot wide, maybe 8"-9". The rest is a thin layer of dirt to either side. After the first rain, when the trench settles, I'll rake the excess back over the trench. A little grass seed and all evidence of the trench will be gone by next summer.
 
 
ZigZag Trench

ZigZag Trench
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We had to make a few curves to avoid coming too close to trees. The trench digger wasn't worried, but I was concerned that we might kill big trees that are either close to the house or help to hide the tower from view.
 
Note the Rohn 55G tower sections to the right.
 
 
The Turn

The Turn
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Here the trench takes about a 90-degree turn. This is another reason I didn't want to run conduit. The alternative was worse. The straight shot from the house to the tower would have gone through an area packed with shallow ledge, and then through the stand of trees that hides the tower from the house (probably killing some of the trees.) A huge patch of poison ivy lives in those woods, too.
 
 
Trench to Tower Base

Trench to Tower Base
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This is the downhill portion of the trench, leading to the tower base. Downhill? What on earth for? Don't you want the tower on the highest point. Well, I'd like that, but it would put the tower in plain sight, which was not an option. Had to sacrifice about 12 feet of height to hide the tower behind a stand of trees. Well, the top will probably peep above the trees, but most of it will be hidden from view. See nice picture of the view below for the reason.
 
 
Cable and Radial Trenches at Tower
 

Cable and Radial Trenches at Base
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Here's the tower end of the cable trench. The plan is to build a utility panel out of pressure-treated lumber. The a NEMA box identical to the ones at the house end will be mounted on the panel. Coax jumpers will run from the heliax through feed-through adapters in the bottom of the box. The control cables will run up through a short section of 4" conduit (probably a 90-degree sweep) into the box. The radial visible on three sides of the base are 50' long and about 8" deep. The depth is so I can pound the ground rods in under grade and have room to cadweld the copper radials to them.
 
The homemade tripod is an idea I got from K1TTT's book. Instead of wood, I used sections of cheap EMT conduit I got at Home Depot. I found the tripod knots on a boy scout website.
 
 
Tower Utility Panel

Tower Utility Panel
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After laying the cables and backfilling the trench, the next task was to build a utility panel next to the tower. I dug a couple of post holes about three feet deep, poured in some quick-set post cement, and inserted a couple of nine-foot 4x4s (cut down from 10 feet.) I nailed a temporary cross plank between the 4x4s, then guyed and leveled the legs. After the cement set, I removed the cross plank and installed the permanent 1.5x6 planks.
 
It doesn't look level, but it is. That's just the effect of the steep hill.
 
 
Preparing the NEMA boxes

NEMA box with suppressors
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This is the NEMA box that will be mounted on the wooden utility panel next to the tower. The two holes on the far left are for the coax links from the hardline, which will be mounted on the panel next to the box. The large hole on the left is for control cables coming in from the tower. The small hole in the right rear corner is for the 1/0 wire connecting the ground panel to the tower system ground. The PVC panel coupler on the right is marking the spot where a large hole will be drilled for the buried control cables coming from the shack.
 
Six Polyphaser coax lightning suppressors are lined up to mark where their holes will be. Rather than passing coax leads into the box and connecting them to panel-mounted suppressors, I like to use bulkhead-mounted suppressors through the box. When doing this, it's important to make sure the ground is well-bonded to the box. One reason I like the bulkhead suppressors is that they're available with a 3KW power rating. The panel-mounted suppressors are only rated for 2KW. Some people have had problems running legal limit through those.
 
 A couple of hole saws are resting on the box, and my drill press is in the background.
 
 
Drilling the NEMA Boxes

NEMA box with drilled holes
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It wasn't easy to position and clamp the box on my drill press. I slowed the speed way down, which you have to do for large holes. Probably could have slowed it down some more. I did a pretty good job drilling holes until I got to the last big hole on the right. The hole saw jammed, the clamps slipped and the box went skidding. The result was the nice gash you can see on the right. A little paint took care of that.
 
 
Drilling a NEMA box for the shack

NEMA box for shack
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This box is for the shack end of the cable run. It only has one large hole on the bottom for the buried cables coming from the tower. There's also a hole for the 1/0 wire connecting the NEMA box to the single point ground. The two large holes in the back are for passing cables through the side of the house.
 
 
Drilling holes in the house

Drill with hole saw
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This is what you need to drill holes in the side of your house. I didn't know exactly how long and extension I'd need, so I went with 12". Turns out a 6" extension would have been fine.
 
 
Hope my wife doesn't see this...

Holes in side of house
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The holes enter the house just above the sill and the drop ceiling in the basement. I can access them simply by sliding a ceiling panel out of the way. From there, they take a 90-degree turn up through a hole in the floor of the shack.
 
You can see the entrance panel for my older antenna farm on the right. That one was professionally installed by an electrician. This time, I just copied his work.
 
We were remodling when the old box was mounted, and expected to re-side the back of the house at some point (that was 10 years ago and we still haven't done it!) The contractor suggested cutting around the NEMA box with a circular saw so it wouldn't have to be removed for re-siding. I did the same for the new box. We'll get around to re-siding one of these days...
 
 
Cables installed at Tower

Cables installed at tower
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The buried control cables from the shack have been pulled into a 90-degree sweep below grade, then up through a short length of PVC into the NEMA box. I used an expansion joint, too, which was overkill since there's not a long conduit run attached to the sweep. The short stub on the left is where control cables from the tower will enter the box. Also on the left is the 1/0 wire that connects the ground panel to the tower system ground.
 
On the right are the two runs of 1-5/8" heliax. These will be cut off above the pipe strap, connectors will be installed, and coax links will run from the connectors into the box via a feed-through bushing.
 
The yellow wire is the end of a 200-foot heavy-duty extension cord for the electric winch used to raise tower sections.
 
 
SO2R 2x6 switch with interlocking relay interface

so2rswitch_2511.jpg
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My old antenna farm uses TopTen A/B and 1x6 switches for SO2R switching. For the new tower, I built the KK1L 2x6 Switch. It's in the larg box in the background. The switch promises to have good isolation in a compact and rugged package. Here's a link to KK1L's description of the switch:
 
 
I like the switch, but I wasn't happy with the idea of using the remote solid-state controller to arbitrate access to the antennas. First, it's possible that one of the logic gates could fail in the high state, causing the same antenna to be selected by both radios. Second, a short in the long cable between the shack and tower could have the same result. Both radios selecting the same antenna would have disasterous results (they would transmit into each other!)

So... I built my own interlocking relay interface. It's in the small box in the foreground. A schematic is provided below. It takes two SPDT relays to protect each band. I put four relays on a Radio Shack prototying board, and stacked three boards in a metal box. Both the SO2R switch and the interlocking relay interface will be installed in the NEMA box next to the tower, protecting the short cable between them. About the only failure mode I can think of would be rectified RF tripping both relays at the same time. Hopefully, the bypass capacitors will keep that from happening.
 
 
Schematic for Interlocking Relay Interface

interlockschematic.jpg
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