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Author Topic: Antenna Transmission Line Installation  (Read 501 times)
KI4HHE
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Posts: 9




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« on: December 01, 2004, 08:10:30 PM »

The following questions may be very basic, and I apologize for my ignorance.  I did some preliminary Google searches, but came up with nothing directly on point.

I have been trying to determine whether an attic based antenna might be possible in my home.  I would like to run the feed line from the antenna to my station behind base boards and thru the walls so the wire will not be visible (otherwise wife will nix the project).  My concept would not anticipate one continuous wire, but a series of wires that were connected.  For example, beginning at my radio the coax would run from the radio to a connector mounted in the wall (kind of like a cable tv connection).  The other end of that connector would run thru the walls to another convenient break point, where there would be another "connection junction."  Installation may be easier if there are multiple "junctions."

Is this a typical/common method of installing the feed line?  Am I way off base here, and does the feed line need to be as continuous as possible?  Is there a "rule of thumb" for the maximum number of "junctions?"  Anyone have a website link where I might read up on this type of thing?

Thanks in advance for any help.

Russ
KI4HHE
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W8JI
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« Reply #1 on: December 01, 2004, 08:31:29 PM »

What power level and frequency are you planning on using?

The answer would vary with that.
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K0ZN
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Posts: 1560




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« Reply #2 on: December 01, 2004, 09:18:52 PM »


As W8JI pointed out in the previous post, there are a lot of details that are unknown which makes a specific answer diffcult.... based on that, I can make some assumptions. (a.) if you are talking about a VHF or UHF antenna system, the connectors are a negative. (I am assuming you were planning on using coax with appropriate connectors at each "junction").
Ordinary "UHF" connectors i.e. PL-259's etc. start causing reflections at LOW VHF; they are "horrible" on high VHF and UHF frequencies, so you would be much better off with a single uninterrupted run of cable.
(b.)  at HF it is less of an issue, especially the low HF bands.

If you "must" have a bunch of junction connections in your coax run, you would be much better off using a higher grade connector like Type "N" connectors. These are more expensive but have better impedance characteristics, especially at VHF & UHF.

 I don't think you were planning this, but I would not recommend running a balanced line, like 450 ohm "ladderline" through a wall in a place where you cannot know EXACTLY what is near the line. Your house also may have insulation with a foil covering which would be bad for a balanced line.

 Lastly, if you think your XYL (wife) will "nix" the project, I would suggest trading HER for a better radio and a bundle of good coax!!  (Just kidding !!)
Remember, beauty is in the eyes of the beholder! To a ham a nice antenna system is beautiful. It is all relative!

73,  K0ZN
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N6AJR
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Posts: 9921




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« Reply #3 on: December 02, 2004, 01:01:35 AM »

go in the attic, drill the hole in the top plates, drop the wire down the wall or use a electrial "fish tape" and run it as 1 wire.  get some rg8x which is good to 440 mhz and 500 watts or so in shorter lengths (under 50 feet) and hook one end to the radio, and the other to the antenna, multiple connectors is just asking for problems
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W8JI
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« Reply #4 on: December 02, 2004, 02:38:54 AM »

I sweep cables and connectors routinely using excellent test gear, and below 250 MHz you can use almost any type of connector without noticable loss or SWR. I don't guess, I actually measure them.    

A few standard UHF style connectors, assuming you install them correctly, would never be a problem below 250 MHz. The exception would be if you happened to use some weird import barrel connectors or elbows. On occasion there are some off-name bands that are a problem.

If you use 432MHz or higher and are concerned about weak signals you would probably want type N's.

Connectors are nowhere near the problem they are thought to be, as long as you install them properly. Just stay away from longer off-brand female connectors like barrel connectors. Use the shortest barrel connectors you can.

A typical UHF-male to UHF female junction only has about .05dB loss at 100 MHz, and virtually all of the loss is in the female section.

73 Tom
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AA4PB
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« Reply #5 on: December 02, 2004, 04:40:56 AM »

The connectors won't hurt anything but it is better not to have connectors inside the walls where you can't get to them. Use a fish tape and run a pull string inside the walls. Then use it to pull a single run of coax thru the walls. A wise thing to do is to pull another pull string along with the coax and leave it in the wall. Then if you ever need to pull an additional coax the string is already in place. Just pull the new coax and another pull string thru the wall.
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WB2WIK
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Posts: 20636




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« Reply #6 on: December 02, 2004, 09:35:50 AM »

I have a different take on this, entirely:

Run the wiring any way you like and look for a new wife!

(I can't imagine how hard I'd be laughing if my XYL ever told me she didn't like the way cables look...)

Good luck with the project!

WB2WIK/6
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K1CJS
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Posts: 6055




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« Reply #7 on: December 02, 2004, 09:50:52 AM »

If it is your house, why not run the co-ax down from the attic outside the house?  If the house is vinyl sided, one of the corner covers will have room underneath.  It is a lot easier than trying to run down inside the walls through firestops, etc., and you'll be able to get at it a lot easier in the future.

Run it down to the basement (if you are able) and then up through the floor to your operating position.

Easier to do, easier to maintain, and easier to take down if you have need to.  And, if you ever have the urge to put an outside antenna up, the co-ax will already be there!
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W0FM
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Posts: 2057




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« Reply #8 on: December 02, 2004, 11:31:05 AM »

Here's a variation on your plan and what Tom, N6AJR suggested.  

Locate a section of wall near your rig where you are able to determine that the inner wall is clear of pipes, wires, etc (by observing the same area from the basement and from the attic, stud finder, etc).  Make sure you don't have "fire stops" horizontally between the vertical studs.  

Stop by the local hardware store and buy a "retro" electrical utility box (like your wall switches and electrical outlets are housed in).  The term "retro" means "retro-fit" so you can install it anytime after the initial wallboard installation by simply cutting a rectangular hole in the drywall that it will fit into.  The box has little "ears" that fold out inside the wall to hold it in place.  No nailing required.  

At the same time, pick up a plastic cover plate (same color and style as your wall switch and outlet covers) with one center hole (like for CATV connectors). Enlarged the single hole to accept the diameter of the coax you plan to run, then make it just a hair bigger.

Using a drywall saw or utility knife, mark and cut an opening in the drywall for the electrical "retro" box.

Go to the attic and drill through the top plate (as N6AJR suggested) for that wall, directly above where you cut the hole in the drywall for the utility box.  Drop the coax (or fish tape, or twine) down into the wall and fish it out of the hole in the drywall by your equipment.  Run the coax out the wall, through the retro utility box and pull out enough to reach your rig with a little to spare.  Push the retro box into the hole cut in the drywall and secure it with its clamping screws.  

Now you can slide the drilled-out cover plate over the rig end of the coax, up to the wall and screw it to the retro box already mounted in the wall. That leaves you a nice looking cover plate with the coax cable exiting from a clean hole in the center of the plate.  Connect the upper end of the coax to your attic antenna.  Add a PL259 at the rig end of the coax and connect it to the rig.

This gives you a single length of coax from the rig to the attic antenna, with no extra connections.  Later, when you decide move the rig to your new 25'x25' ham shack addition (new wife by that time, of course), you simply pull out the coax, install a blank plastic cover plate over the utility box and the room is as good as new.

I've done this several times with great results.  It's quick, clean and easy to walk away from.

Good luck,

Terry, WØFM
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N3ZKP
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Posts: 2008




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« Reply #9 on: December 02, 2004, 12:07:21 PM »

I second WB2WIK/6's thoughts.

I cannot imagine my wife having any say in how I run cables or anything else radio related any more than I can imagine my telling her how to deal with her hobbies!

Lon
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WB6BYU
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Posts: 13488




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« Reply #10 on: December 02, 2004, 12:26:28 PM »

It should work just fine that way, as long as the coax
connectors are properly installed on the cable.

A couple of suggestions, though:

1) Most houses are required to have fire stops nailed
between the studs, usually around half way up the wall.
You'll need a drill bit on a LONG shank to get through
this, and sticking a cable through the hole from several
feet above it may not be an easy task.  A stiff length
of wire might be the best approach.

2) Exterior walls will be filled with insulation in most
parts of the country.  Besides, there is usually more
room to work over an interior wall because the roof
is higher.

3)  While you are at it, run at least two cables instead
of just one.  There should be enough room in a standard
outlet plate for two connectors, and that makes it easier
for you to upgrade in the future (adding an additional
antenna for 6m or HF, for example).
~
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AA4PB
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Posts: 12993




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« Reply #11 on: December 02, 2004, 06:11:16 PM »

Most houses are required to have fire stops nailed between the studs, usually around half way up the wall.
----------------------------------------------------
I imagine that depends on your local codes. I've done a fair amount of work running network and electrical cables in walls in MD and VA (both commercial and residential buildings) and I've not run across fire stops in the walls. Insulation is a problem in the exterior walls.

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EXWA2SWA
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Posts: 158




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« Reply #12 on: December 03, 2004, 11:18:15 AM »

I cheated: I ran the coax up through a closet that is right next to my operating position. Sadly, the ceiling of the closet was about a foot lower than the ceiling of the adjoining room. So there were two 1 foot runs of coax visible from inside the shower ... until I put a plastic plant in front of them and gained points for my decorating creativity.

Now that I know one of the feeds is too long, I'll just put a coax butt-connector (female - female) between the old and the new and use the old to pull the new through.
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N0TONE
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Posts: 173




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« Reply #13 on: December 03, 2004, 12:04:10 PM »

As W8JI said, the connectors are no problem at all, as long as you install them correctly and avoid real cheap ones.

I have found a very quick method for dealing with this.  I find one of those PVC vent pipes, that does nothing more than vent a drain.  These pips represent a path from roof all the way down to whatever floor the plumbing fixture sits in.  I may feed the cable in the top, or if it's an attic antenna, I drill a hole in the attic portion.  Then drill a hole down near where I need the cable to end up.  In my case, I find the pipe in the basement, and drill there.  It takes some fishing to get the cable through - ( actually find that 1/8" chain is the easiest thing, dropped down from above and snagged with a hook made from something like #14 solid copper wire.  Then pull the cable up from underneath.  Now I have cable exposed in the basement, and then I drill a hole in the floor right under where the radio is.  The hole is adjacent to a baseboard, but not under the wall - that's too hard.  So the cable comes out from under the carpet.  When I got to move, I just pull the cable out.  The carpet covers the hole.  A little silicone-based caulk, the color of the pipe, fills the two pipe holes.

The entire process takes about a half hour.

AM
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WB4QNG
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Posts: 362




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« Reply #14 on: December 09, 2004, 06:47:17 PM »

I did the same as the other guy ran them through the closet. I drilled a hole in the wall and when I moved I put a blank cover over the whole. Cut the hole in the wall the same height as the outlet boxes. When I changed rooms I ran the cable under the door of the closet. The only problem I see with your set up is who in the world only wants one antenna. I think I have 8 different antennas in my attic with eight feedlines comming into my room
Terry
WB4QNG
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