Friday, June 28, 2019

Coaxial Cable Entrance Box Installation

Plans are still on to bore the holes either Saturday or Sunday, weather permitting.

It was 96* here today, and the NWS is forecasting 94* on Sunday....BUT.....There;s some weather forming up right now, the winds have picked up, the temperature is falling, and the barometer is 29.85 and rising. The lightning detector has been going off sporadically, indicating distances of 15~30kM, and I've seen lightning in the distance. So we'll see!

There's still plenty to do, and one of the tasks on the punch-list was getting the cable entrance finalized, and installed. It was originally going to have a single connection to the wire antenna, and have the Choke Balun/Line Isolator inside. and the control cable for the autocoupler.

It looked like this, before 'mission creep' set in:


WELL.....one the things I learned in getting the wire antenna up, and reading tons of books on antennas and transmission lines, is that the choke balun/line isolator MUST go at the antenna. It's entire purpose is to keep currents off the outside of the shield, and since those currents originate at the transmission line/antenna interface, that's where you put it. Now I've read this for years, but didn't understand the exact mechanism of how the currents got on the outside of the shield in the first place. Like a lot of Hams, I pretty much assumed the currents on the outside of the shield were induced on the shield by the radiating element's RF field.....WRONG! The currents get on the outside of the shield At The Feedpoint. It's a subtle thing, but the RF energy not only "sees" one side of the antenna as a conductor, but also "sees" the outside of the shield as another parallel path, and unless you choke the current at the feedpoint, the outside of the side becomes part of the antenna, and can cause a lot of mischief.

SO.....the Line Isolator has been removed from the outside-of-the-house enclosure, and has been relocated to the enclosure for the SGC autocoupler, as close to the input of the tuner as possible. The "permanent" 20 Meter vertical was also being put through it's paces and measurements during this learning period, and it has a Home Brew choke balun that looks like this:


Quite simple, almost 'free', and very effective. Just a coil of coax, nicely wound (NOT "Scramble Wound"), and secured to the antenna as close as practically possible to the feedpoint.

So the vertical is proved in, and will get mounted to it's new 4x4 post in the next week or so. It'll just get removed from the tripod, and attached to the post as-is. It works. It ain't broke. I don't need to "fix it", and the only way to "improve" it would be to raise it higher and add another radial or two.

The new wire antenna has been fabricated, the enclosure and mounting structure for the SGC autocoupler has been fabricated, and it'll be ready-to-install as soon as the quickrete sets on the post.

So the whole question of the cable entrance box gets easier, as I now have the outside box pretty empty, except for connectors, and inside box was always going to be pretty empty, except for the connectors.

Well, I got off-the-dime last week, and finished making some more back-up plates to support the connectors in the box.

Here's a pair of Type UHF bulkhead connectors installed using the home brew aluminum plates:


Lather, rinse, and repeat until both boxes have four of these connectors in them. Oooops.....didn't take any pix of them before I mounted them outside and inside 'cuz I was on a roll!

Outside box, solidly mounted:


From a bit further back:



And on the inside:



The connectors are on the bottom of the enclosures for weather proofing and appearance reasons, and wonder of wonders.......I was within 1/8" of getting things to line up perfectly.

So this item is pretty much crossed off. I still have to make four RG-8X 'jumper cables' to pass through the wall and a few dozen other things to do, and the poor Supra still has the winter dust on her.

Gotta get back on that car! Winter caught me off guard last year, and now I have to get that Supra Swing back.....

8 comments:

  1. Nice work. To pay the ultimate compliments, I think it looks "shipshape" and "squared away."

    "Mission Creep."
    The mission started by taking the bathroom door outside for a touch of planing to remove the rub.
    My wife pointed out that one of the glued joints in the door looked to be loose.
    Thirteen of the fourteen glued joints were loose, and the fourteenth came loose with minor persuasion.
    And what does the ability to thread 1/2" pipe have to do with the bathroom door?
    My four bar clamps aren't long enough to go top to bottom, but they are easily stretched with 1/2" pipe couplings and threaded pipe.
    "Mission Creep" indeed!

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    1. Thanks, John

      (GROAN!) Don't get me started on home "improvement" projects! The side door on the garage either needs to be replaced or rebuilt. ALL the glue joints are loose, and the door is tweaked as much as it can be, and still fit in the frame. I could take it off, reglue it, and clamp it together, but it's a 1977-vintage wood door with big glass windows, and it's a MAJOR heat leak out of the garage in the winter. I have to replace it before next winter, but there's other stuff to do right now....

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    2. Usually, to fix one thing you have to fix five others.

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    3. If it was a painted pine door we would simply replace it.
      But it is stained and coated with poly, the hinges are square, and not the easily routed hinges, and when we did all the work, we also removed two of the wood panels, and installed two crackle finished plastic "panes" to let the light through. And we made the new molding to put the plastic panels in the door.
      Other than the failed glue joints, (I have to admit that I'm chuckling at myself) the door is sound, and would be a ton of work to replace.
      The threading of the pipe for the clamps went well.
      We were going to start gluing today, but we spent time doing other stuff and then lounged by the pool.

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    4. Ahhhh, yes...."Custom Work". I'm going to replace the door with a fiberglass one, with a couple of small "frosted" windows in it to let some light in. The hinges are identical in spacing and mounting to the ones on prehung doors, so I'll get one of those and wind up tossing the frame or cutting it up for some of those "misc chunks of wood" you always seem to need in the garage/workshop.

      Was going to dig the post holes today, BUT....the grandson came over, it started sprinkling, and I had some housework to knock out.

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  2. 96... we had a storm blow through last night and it cooled things down, thank God.

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    1. It got to 91* here today around 1345, and then a front came through dropping the temp about 20* in two hours. Storm clouds everywhere but here. We just got some sprinkles, so I watered the lawn.

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Keep it civil, please....