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Author Topic: Ladder LIne through cinder block  (Read 11858 times)

Posts: 26

« on: December 24, 2009, 05:26:55 AM »

The new shack is in the basement (or will be soon). My first antenna at the new place will be a couplet fed with 6" ladder line. I have to go through a cinder block wall.

While the wall is 8" thick, cinder block has voids. I suspect the thing to do is to drill two half inch holes 6" apart. measured from the center of one block above grade (of course). I intend to use a plastic "plate" (e.g. 2"x8" lexan) on either side of the wall as a large washer and run 1/4 or 3/16 inch threaded rod in the center of each hole. (anyone know where to find about 20" of brass threaded rod?) This will provide a mechanically secure attachment point inside and out.

If the cinder block is mostly dry (painted inside and out and above grade) I think the loss induced by the physical presence of the block should be not very bad. By experimentation it is determined that there is no rebar in the block. Since everything is symmetric I think that this 8" trip through the cinder block will not induce feed line radiation.

Anyone have better suggestions? Experience doing this? Has anyone ever measured loss running ladder line through various types of wall (especially cinder block)?

Posts: 7718

« Reply #1 on: December 24, 2009, 08:16:02 AM »

There will be an impedance discontinuity and dielectric loss where the line passes through the wall of the cinder block.

The paper available at the link above has data that can be used to calculate the loss and impedance discontinuity. Fig. 8 gives the relative dielectric constant based on the water-to-concrete ratio. The plot appears to be C/W and not W/C.

An emperical approach to determining the loss, if that is your goal, is to run 100 watts for a period of time and to measure the cinder block temperature rise. Allow the cinder block to cool. Now substitute a known heat source (resistor bonded to the cinder block) and apply power for the same time period. Do this until the same temperature rise in the same time period is achieved and you will know the RF loss.

Or, build it, use it and don't worry about it.

Posts: 217

« Reply #2 on: December 24, 2009, 09:57:54 AM »

Some cinder block has a concrete slurry fill.

There have been postings showing favorable results in using 2 sections of RG-8x, in parallel, to replace the ladder line in this sort of situation.  Just keep the spacing correct and use the center conductors as the connection points.

I have a remote 4:1 current balun outside my shack window and feed it with coax, then do the open wire feedline connection at the balun.  Lots easier that the above suggestion but, it too, has its drawbacks - if you are using a tuner with a built in balun to feed the antenna then the first suggestion will work fine.

When weather permits you may wish to use a concrete saw to remove a section of the cinder block and install some thick Lexan on the inside and outside.  This will facilitate future needs (they arise as the antenna farm increases).

Posts: 21808

« Reply #3 on: December 24, 2009, 03:37:54 PM »

I've run ladder line "through" cinder block before.

Your approach sounds pretty good and I'll bet it will work fine; however what I did is hire a guy with a concrete saw to make a 4" diameter hole right through the block, and install a plastic (PVC or ABS?  Not really sure what these are made of, but they're some sort of plastic...) dryer vent with an attached 4" diameter pipe: $4 at Home Depot.

The dryer vent looks "normal" on the outside, as people are used to seeing these, and it doesn't have to be removed when you sell the house.  The 4" plastic pipe has a lot of room in it for clearance to the ladder line; I just stuffed foam rubber insulation all around the ladder line to keep it roughly "centered" in the dryer vent and 4" pipe, which not only added a good insulator around the line, but also kept out the bugs and drafts.  A win-win for a $4 accessory and paying a local guy $20 to make the hole...

Posts: 1837

« Reply #4 on: December 24, 2009, 09:05:53 PM »

Are there windows in the basement?  We used to just replace one of the window panes with a piece of clear plastic and run the ladder line through that using porcelain insulators or you could just use screws & nuts.  Lowes and Home Depot sell the plastic and can cut it to size for you.

Posts: 625

« Reply #5 on: December 24, 2009, 09:28:42 PM »

Since the antenna is not matched to the feed line and you are matching with a tuner anyway, why do you care about the distance between the feed line wires.  Most of the field is between the two wires of the T line, so reduce the spacing down before entering the wall and use a short piece of window line (the stuff with the windows punched into it).  Run it through a hole in the block lined with some plastic pipe.  There will be an impedance bump, but since it is an unmatched system anyway, why worry.  Just make a match using the tuner.  If a match is hard to obtain, change the feed line length until you get something that works.

The biggest thing to watch out for is places where you have a high voltage on the feed line.  At those points you need to make sure you have sufficient spacing to prevent any flash over.  So adding some plastic pipe or stand offs would be in order, anywhere you might get an arc.

Ladder line systems are not nearly as particular as many posts on eham would have you believe.  Just be prepared for a few tweaks if encounter lenghth or spacing issues.

Posts: 26

« Reply #6 on: December 27, 2009, 10:15:26 AM »

WA7NCL says: most of the field is between the two wires of the feed line - so, just srink it down some. This sounds like a good idea - as a matter of fact, the post on the back of the Johnson Matchbox are not 6" apart, but I've been using it with 6" Ladder line for some time.

Perhaps a 4" dia. hole with PVC liner to hold end caps parallel and brass screws for studs at each end? this would give a structually sound pass through that will be weather tight with just a little caulk.

Hmm...I could even mount a nifty short throw knife switch I have on the outside and use a plastic rod to work the switch so the ladder line could be grounded outside when not in use. I could cover the switch with one of the dryer vent thingies.

Posts: 705

« Reply #7 on: January 03, 2010, 03:10:21 PM »

When I moved into my current residence in 2002, I wanted to drill through a concrete block wall and insert a 4-inch diameter PVC pipe for feedlines, control cables, etc.

I went to the local tool rental shop. The guy there told me I needed a hammer drill. I rented one, took it home, and it drilled through the concrete block like a hot knife through butter. Frankly, I'm not the home handyman type and thought this would be difficult. Wrong! I drilled the hole, installed my previously cut PVC, sealed the hole around the edges and had the rented hammer drill back to the store -- all within one hour.

While I thought this would be a hard project, it was easy with the right tool. Go for it. I've also gone into basements through dryer events and basement window panes too in the past. All work fine.

73, N4KZ

Posts: 59

« Reply #8 on: January 14, 2010, 05:29:53 PM »

What mainly you want to look out for with Cinder Block if there is any Rebar inside the cinder block, especially if it was used for the Foundation. So know where you are drilling first??

Hope that helps.

73, de Ron, W6BR

Posts: 40

« Reply #9 on: January 15, 2010, 10:42:00 PM »

1/4-20 brass threaded rod 24" long is available at McMaster Carr for $4.60. See
   I've punched 1-1/2" wide holes through my basement wall concrete cinder block with a simple masonry bit operated by an electric drill, then enlarged by a 3/4" diameter star drill bit.  I used a 18" long 3/16" diameter masonry bit to drill a single hole completely through the cinder block, this was to assure the inside & outside holes would line up.  Star drills are hand operated, hammered like a chisel & used to drill holes in concrete or stone.  I was pretty sure my blocks were conventional cinderblock with 3 large voids predictably spaced, no fill and no rebar, that proved to be true.

Posts: 2414

« Reply #10 on: January 31, 2010, 04:12:25 PM »

If you're concerned about how the job will look, a concrete coring company will core any size hole up over 12" in diameter for you, and will leave a perfect core that can be replaced should you ever want to fill it up.  The hole is perfect with sharp edges, and no breakout, a common occurance with cinderblock especially when using tools usually available to the "weekend warrior".

The link below shows a 7" core in my poured concrete basement wall. The outer surface is covered with an aluminum plate.
« Last Edit: January 31, 2010, 04:40:15 PM by Tom Hybiske » Logged
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