Antenna mast construction (masonry chimney as a base)

#1
From what I've gathered here so far, the height of my antenna is going to be an important factor if I have any hope of pulling in any NYC stations. I have a 22' masonry chimney on the side of my house constructed of 16 x 16 chimney block with a good solid (and intact) parge coat, so it should make a sturdy base for an antenna mast. I was thinking of simply finding a piece of Schedule 40 black pipe in the diameter I need for whatever antenna I settle on and using pipe clamps like these along with Tapcon concrete anchors to attach the mast to the side of the chimney. McMaster-Carr sells heavy gauge stainless steel versions of the style of pipe clamp in the link fairly cheap. I will paint the mast with black POR-15 which is about the toughest coating you can put on metal short of powdercoat. My plan was to source a 10 or 12' length of pipe since I'll need at least 2-3' of overlap between the mast and the chimney in order to securely fasten it. I think this will make a pretty robust mast which hopefully will help with reception on windy days. Frequent high winds are not really an issue around here, just some strong gusts whenever a storm blows through. Anyone see any problems with this approach? It seems like a pretty simple thing, but I'm sure there could be things that I'm missing. I wish I could go higher, but I'm not sure how I would guy it if I did and as it is my wife is giving me a pass on putting an antenna on the roof in the first place, let alone one up so high you can see it from a block over :becky:
 

MrPogi

Moderator, , Webmaster of Cache Free TV
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#2
I think that would work.

I don't know what it is about wives objecting to antennas, but it seems pretty common. Most of them come around if you can somehow share the savings with them. Since my wife was paying the DirecTV bill, she came around pretty quickly!
 
#3
I don't know what it is about wives objecting to antennas, but it seems pretty common. Most of them come around if you can somehow share the savings with them. Since my wife was paying the DirecTV bill, she came around pretty quickly!
LOL...my wife is onboard for the saving money part. This is just one part of paring down expenses to the point that she can stay home with our daughter instead having to go back to work (mostly to pay for childcare)-I guess of course the other selling point is the fact that not only will we be saving money, but that a large and powerful antenna is necessary to get good reception. Reception that she'll be grateful for when home alone with a baby for 6-7 hours a day :D
 

Fringe Reception

Super Moderator, Chief Content Editor
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#4
Badfish,

I wouldn't use the 'brackets' you have in mind because your antenna system will rely on only two small fasteners per bracket to support the entire works and they are not designed to hold tubing that is 'trying' to rotate. They are conduit clamps. Generally, I don't like to use a chimney but when its the best option I use Chimney Mounts available from Radio Shack.

They use stainless steel strapping that wrap around and 'hug' the chimney. Your system would depend on the integrity of individual bricks of the side of your chimney. The Rad Shack mount supports the mast on a corner where the chimney is strongest.

Below is a photo taken (before guy wires were added) of a setup I built using two 10 foot masts plugged together. Although not pictured, the chimney-mount straps are about 5 feet apart from each other to spread the load between the top and bottom of the 6 foot tall chimney.

I have been accused many times of over-engineering my projects, but it seems to me if someone specifically designed a chimney mount and it has became a standardized method to mount antennas for 40+ years and it is still available (cheap) there must be something to them that works and is dependable, why reinvent the wheel?

Jim

 
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#6
I wouldn't use the 'brackets' you have in mind because your antenna system will rely on only two small fasteners per bracket to support the entire works and they are not designed to hold tubing that is 'trying' to rotate. They are conduit clamps. Generally, I don't like to use a chimney but when its the best option I use Chimney Mounts available from Radio Shack. They use stainless steel strapping that wrap around and 'hug' the chimney. Your system would depend on the integrity of individual bricks of the side of your chimney. The Rad Shack mount supports the mast on a corner where the chimney is strongest...I have been accused many times of over-engineering my projects, but it seems to me if someone specifically designed a chimney mount and it has became a standardized method to mount antennas for 40+ years and it is still available (cheap) there must be something to them that works and is dependable, why reinvent the wheel?
I'm a chronic "over-engineerer" and sometimes cannot help myself :D Below is picture of a gate I built that leads to the backyard at the end of my driveway:



I needed something to keep the two gate posts from sagging inward from the weight of the 4' x 6' doors, so I decided to build a composite beam of sorts out of a 4x6 timber and two 2x8s, screwed, glued, and bolted. The uprights are 4x6s set 4' in the ground with 4x4 angle braces for stiffness. My civil engineer BIL did some math on it and said that the span would support 3000lbs without much trouble. Good to know if I ever need to pull the Powerstroke out of my truck :D
 

n2rj

Moderator
Staff member
#7
The standard chimney mount is fine. The only concern I have is that if you use your chimney that the antenna will get smoke on it.

I generally hate chimney mounted antennas for that very reason.
 
#9
The standard chimney mount is fine. The only concern I have is that if you use your chimney that the antenna will get smoke on it.

I generally hate chimney mounted antennas for that very reason.
Rut Row...I didn't really think of smoke as a concern-how much can it affect performance? The oil burner (vented through the masonry chimney which I intend to mount the antenna on) burns about 85% efficient, so there's no visible soot (I'm assuming the concern is soot buildup on the elements?), but located about 10' away on the same side of the house is the chimney for my wood burning furnace, which can produce sooty smoke depending on the type of wood and how much air I'm giving it. Will the wood smoke foul the elements and give me reception problems?
 

n2rj

Moderator
Staff member
#10
Oil burners should be fine.

If you put it on the woodburner's chimney that's a different story. The soot buildup is acidic and invites corrosion.

I would also be concerned about the structural integrity of the chimney being compromised, since the antenna and mast in the wind is essentially a giant lever.
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#11
Badfish,

As I wrote above, I prefer to not use chimneys because smoke deposits (carbon/creosote) could be a problem and if the antenna is very close to the top of the chimney, high heat (and smoke chemicals) could eat or reduce the lifespan of the plastic parts. The antenna installation photo above, is the second system I installed on the same chimney mount; the first was around 1985. The first setup was a very large antenna similar in size to the one you are concidering buying. It had to be big to be able to receive two low-band VHF Network Stations, channels 4 and 5 at a range of 35-40 miles.

When I redid their antenna system a couple years ago I was astonished the large 'cut-to-channel-4' Yagi almost fell apart in my hands. Sure, after twenty-some years, degradation would be expected but this was interesting. The main boom and elements were perfect but the center rivets had disintegrated: the antenna came apart in my hands like a kit.

My guess is the rivits were a different alloy than the boom and elements and electrolysis 'ate' them over the years. This was a wood-burning fireplace/chimney and the primary source of heat for the home. I didn't see any carbon deposits on the antenna.

Jim
 

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