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Putting antennas on house chimneys
I've no real experience of putting up antennas on the chimney of a house.
Obviously, I must not overload the chimney breast. I'm thinking about putting up the following: ______ Discone / | \ __ / || \ A | __ ___|x___ 5 ele.2m yagi | B | | __ |x| 5 ele. marine yagi | | C | | | __ |x| 5 ele. FM yagi. | | D | | __ | / \ Rotator /__\ | | ______ | | | Chimney | | | | | I'm wondering about the spacings, A, B, C, and D. A, spacing between bottom of the discone and the boom of 2 m yagi. B, spacing between boom of 2m yagi and boom of marine band yagi. C, spacing between boom of marine band yagi and boom of FM yagi. D, spacing between boom of FM yago and top of rotator. As for the mast, I'm thinking what about 1.5" steel tube. As for rotator. No idea what model I'd need. Any thoughts? Am I trying to be too ambitious? I could leave out the marine yagi if I had to. Thanks. Rich. |
I'm wondering if your chimney will handle the weight ?
Robert "Richard" wrote in message ... I've no real experience of putting up antennas on the chimney of a house. Obviously, I must not overload the chimney breast. I'm thinking about putting up the following: ______ Discone / | \ __ / || \ A | __ ___|x___ 5 ele.2m yagi | B | | __ |x| 5 ele. marine yagi | | C | | | __ |x| 5 ele. FM yagi. | | D | | __ | / \ Rotator /__\ | | ______ | | | Chimney | | | | | I'm wondering about the spacings, A, B, C, and D. A, spacing between bottom of the discone and the boom of 2 m yagi. B, spacing between boom of 2m yagi and boom of marine band yagi. C, spacing between boom of marine band yagi and boom of FM yagi. D, spacing between boom of FM yago and top of rotator. As for the mast, I'm thinking what about 1.5" steel tube. As for rotator. No idea what model I'd need. Any thoughts? Am I trying to be too ambitious? I could leave out the marine yagi if I had to. Thanks. Rich. |
On Tue, 17 Feb 2004 17:47:39 -0000, "Richard"
wrote: I'm wondering about the spacings, A, B, C, and D. Hi Richard, You should be thinking more of the tensile failure of the brick mortar leveraged by the moment of the load above. Chimneys are very strong to compressive loads, and as brittle as candy to torsion. The upshot of this is that on a windy night you may find the chimney in your bed. 73's Richard Clark, KB7QHC |
I've no real experience of putting up antennas on the chimney of a house.
Obviously, I must not overload the chimney breast. I think your antenna plan is workable. At one qth I had up a 2 element 10m yagi and a 5 el 2m yagi on a chimney mount. Replaced those with a 2 el 15/10 quad for a while. This was with a Radio Shack chimney mount. Just the chimney mount by itself was too flimsy. I found that it was necessary to add a set of guys, attached just below the rotator and running to the roof corners. The guys made the whole thing much more secure and took some of the windload off of the chimney. Torsten N4OGW |
I've no real experience of putting up antennas on the chimney of a house. I have seen chimeys come down in severe wx with just large TV antennas on them. I guess it would be dependent not only on the structural integrity of the chimney but also physical size but I certainly would be careful. I don't know your particulars but wouldn't it be better to have something bolted on the side of the house even with the insurance issues???? Good Luck and God Bless Tom KI3R |
Richard, I'm not going to tell you that it's workable or not, I have no honest way of doing so. At least not without seeing your chimney, or rather putting my hands on it to see what condition it's in and how well it's put together, etc, etc. The most realistic thing anyone can tell you is that in general, chimneys are not built to support anything except themselves, and do not do well if large 'wind loads' are placed on them. The other side of that coin is that people have 'gotten- away' with mounting antennas on chimneys for years with no problems at all. Just depends on the chimney and how much 'stuff' you try to tack onto them. Something else you may not have thought of is what does the smoke and other combustion products do to the antennas and rotor on the chimney? Of course, that depends on if you ever use the 'fireplace', or not. What you burn if you do use it, and how often you have it cleaned (if ever). You haven't lived until you've had a chimney fire (LOL), inside or outside the flue! 'Doc |
"Richard Clark" wrote in message ... On Tue, 17 Feb 2004 17:47:39 -0000, "Richard" wrote: I'm wondering about the spacings, A, B, C, and D. Hi Richard, You should be thinking more of the tensile failure of the brick mortar leveraged by the moment of the load above. Chimneys are very strong to compressive loads, and as brittle as candy to torsion. The upshot of this is that on a windy night you may find the chimney in your bed. 73's Richard Clark, KB7QHC ======================== Better get in a stock of viagra. Brickwork is weakest when under a tensile stress. So the chimney brickwork is most likely to fail under tension due to sideways thrust of the wind. Placing the chimney under torsion causes only a horizontal shear force on the brickwork to which it is more able to resist. ---- Reg. |
Richard wrote:
I've no real experience of putting up antennas on the chimney of a house. Obviously, I must not overload the chimney breast. I'm thinking about putting up the following: ______ Discone / | \ __ / || \ A | __ ___|x___ 5 ele.2m yagi | B | | __ |x| 5 ele. marine yagi | | C | | | __ |x| 5 ele. FM yagi. | | D | | __ | / \ Rotator /__\ | | ______ | | | Chimney | | | | | I'm wondering about the spacings, A, B, C, and D. A, spacing between bottom of the discone and the boom of 2 m yagi. B, spacing between boom of 2m yagi and boom of marine band yagi. C, spacing between boom of marine band yagi and boom of FM yagi. D, spacing between boom of FM yago and top of rotator. As for the mast, I'm thinking what about 1.5" steel tube. As for rotator. No idea what model I'd need. Any thoughts? Am I trying to be too ambitious? I could leave out the marine yagi if I had to. Thanks. Rich. Check to make sure there are no ordnances against attaching structures to chimneys. You would do better with a tripod mount on the roof. Hope this helps... Irv VE6BP -- -------------------------------------- Diagnosed Type II Diabetes March 5 2001 Beating it with diet and exercise! 297/215/210 (to be revised lower) 58"/43"(!)/44" (already lower too!) -------------------------------------- Visit my HomePage at http://members.shaw.ca/finkirv/ Visit my very special website at http://members.shaw.ca/finkirv4/ Visit my CFSRS/CFIOG ONLINE OLDTIMERS website at http://members.shaw.ca/finkirv5/ -------------------- Irv Finkleman, Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP Calgary, Alberta, Canada |
Reg Edwards wrote:
"Richard Clark" wrote in message ... On Tue, 17 Feb 2004 17:47:39 -0000, "Richard" wrote: I'm wondering about the spacings, A, B, C, and D. Hi Richard, You should be thinking more of the tensile failure of the brick mortar leveraged by the moment of the load above. Chimneys are very strong to compressive loads, and as brittle as candy to torsion. The upshot of this is that on a windy night you may find the chimney in your bed. 73's Richard Clark, KB7QHC ======================== Better get in a stock of viagra. Brickwork is weakest when under a tensile stress. So the chimney brickwork is most likely to fail under tension due to sideways thrust of the wind. Placing the chimney under torsion causes only a horizontal shear force on the brickwork to which it is more able to resist. ---- Reg. All this presupposes the chimney is brick. Mine is cast concrete and has had a big TV antenna on it for years and this is a high wind area. There is a smoke and soot problem and I only run the fireplace a few times a year. I wouldn't put an expensive ham antenna (or a rotor) up there. -- Jim Pennino Remove -spam-sux to reply. |
On Tue, 17 Feb 2004 20:01:40 +0000 (UTC), "Reg Edwards"
wrote: sideways thrust of the wind. = Placing the chimney under torsion |
[This post is sent again in plain text (cannot avoid that). I've
used a monospaced font type, "courier new", font size, "smaller" to view the page on my PC. To correctly view the ASCII art, you ay need to adjust your viewing font (ToolsOptionsReadFonts) to: Proportional Font: "Courier new" Font size: "smaller".] I've no real experience of putting up antennas on the chimney of a house. Obviously, I must not overload the chimney breast. I'm thinking about putting up the following: _______ Discone / | \ __ / || \ A | __ ___|x___ 5 ele.2m yagi | B | | __ |x| 5 ele. marine yagi | | C | | | __ |x| 5 ele. FM yagi. | | D | | __ | / \ Rotator /___\ | | ______ | | | Chimney | | | | | | I'm wondering about the spacings, A, B, C, and D. A, spacing between bottom of the discone and the boom of 2 m yagi. B, spacing between boom of 2m yagi and boom of marine band yagi. C, spacing between boom of marine band yagi and boom of FM yagi. D, spacing between boom of FM yago and top of rotator. As for the mast, I'm thinking what about 1.5" steel tube. As for rotator. No idea what model I'd need. Any thoughts? Am I trying to be too ambitious? I could leave out the marine yagi if I had to. Thanks. Rich. |
"Richard Clark" wrote in message ... On Tue, 17 Feb 2004 17:47:39 -0000, "Richard" wrote: I'm wondering about the spacings, A, B, C, and D. Hi Richard, You should be thinking more of the tensile failure of the brick mortar leveraged by the moment of the load above. Chimneys are very strong to compressive loads, and as brittle as candy to torsion. Hi, I confirmed too that you will experiment problems with the maconnery. I attached the end of a G5RV to my chimney, fine, no problem for years, but the vertical damaged the bricks and the cement udner high wind. A small roof pylon (2-3m high) is by far preferable and more secure. Thierry ON4SKY http://www.astrosurf.com/lombry/menu-qsl.htm The upshot of this is that on a windy night you may find the chimney in your bed. 73's Richard Clark, KB7QHC |
I wouldn't do it.
"bunnydawg" wrote in message .. . I'm wondering if your chimney will handle the weight ? Robert "Richard" wrote in message ... I've no real experience of putting up antennas on the chimney of a house. Obviously, I must not overload the chimney breast. I'm thinking about putting up the following: ______ Discone / | \ __ / || \ A | __ ___|x___ 5 ele.2m yagi | B | | __ |x| 5 ele. marine yagi | | C | | | __ |x| 5 ele. FM yagi. | | D | | __ | / \ Rotator /__\ | | ______ | | | Chimney | | | | | I'm wondering about the spacings, A, B, C, and D. A, spacing between bottom of the discone and the boom of 2 m yagi. B, spacing between boom of 2m yagi and boom of marine band yagi. C, spacing between boom of marine band yagi and boom of FM yagi. D, spacing between boom of FM yago and top of rotator. As for the mast, I'm thinking what about 1.5" steel tube. As for rotator. No idea what model I'd need. Any thoughts? Am I trying to be too ambitious? I could leave out the marine yagi if I had to. Thanks. Rich. |
On Tue, 17 Feb 2004 22:41:16 -0000, "Richard"
wrote: [This post is sent again in plain text (cannot avoid that). I've used a monospaced font type, "courier new", font size, "smaller" to view the page on my PC. To correctly view the ASCII art, you ay need to adjust your viewing font (ToolsOptionsReadFonts) to: Proportional Font: "Courier new" Font size: "smaller".] Hi Richard, It may look good to you, but for many it remains sloppy. The convention of ASCII-Doodles is to employ fixed pitch fonts. This is available to everyone. A, spacing between bottom of the discone and the boom of 2 m yagi. 0.5M to 1M B, spacing between boom of 2m yagi and boom of marine band yagi. 0.5M to 1M C, spacing between boom of marine band yagi and boom of FM yagi. 0.5M to 1M D, spacing between boom of FM yago and top of rotator. 0.5M Proximity is more likely to disturb the depth of nulls than to rob gain. Proximity will also pull resonant frequency. Recommendations will run the gamut where a purist would demand 1 to 5 wavelengths. Practice often accepts much less when offset by sweat-equity (more tuning and trimming on your part). Don't forget guy wires to preserve the mortar (its not the brick that breaks); and don't forget to break up the guys to prevent their resonance effects (or use non-conductive guys). 73's Richard Clark, KB7QHC |
Hi,
One thing I have not seen in previous replies, If you use a band clamp to attach the mast to the chimney, water can get behind the metal band and when it freezes, cause damage to the brick. In warm weather, the bricks expand and the metal bands damage the bricks. I'm not an engineer but another post recommended to use guy wires so to reduce windload off the chimney. I don't believe this will reduce windload at all, the guys will be attached to the mast only and not the actual antenna so no reduction in windload. Best to avoid using the chimney and attach the mast to the house at the eave using long bolts and nuts attached to some pressure treated (and painted) 2x4's on outside and inside the attic. stronger and you don't have to worry about the coax getting too hot from the heat of the chimney exhaust. mick |
A chimney is one of the worst places you can locate an antenna. They
appear to be handy, but even on an old chimney there are corrosive gases that will really do a job on Aluminum. Gas fired furnaces are bad, wood is worse,a nd coal is terrible. If the chimney appears to be solid enough to hold a small antenna, (they rarely are strong enough to hold much more than a VHF, or TV antenna) then give all the aluminum about 4 or 5 coats of clear Krylon. Give the coax connector and attach points several coats of liquid electrical tape. Even then it most likely will have to be done every year or two at best. Steel mast fittings will rust beyond repair within just a few months. They'll hold, but usually have to be cut off, or will twist off when an attempt to remove the nuts is made. If at all possible, put the antennas some where other than on a chimney. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com |
"Richard Clark" wrote in message ... On Tue, 17 Feb 2004 22:41:16 -0000, "Richard" wrote: [This post is sent again in plain text (cannot avoid that). I've used a monospaced font type, "courier new", font size, "smaller" to view the page on my PC. To correctly view the ASCII art, you ay need to adjust your viewing font (ToolsOptionsReadFonts) to: Proportional Font: "Courier new" Font size: "smaller".] Hi Richard, It may look good to you, but for many it remains sloppy. The convention of ASCII-Doodles is to employ fixed pitch fonts. This is available to everyone. Hi. I have used fixed pitch on the second post. Courier new is fixed pitch/monospaced. I beleive the viewer though has to change the veiwing font to courier new. |
When a body in the form of a rod or a tube, albeit a short rod, is placed
under torsion, ie., it is subjected to a TWISTING MOMENT, then SHEAR stresses are set up in it. The shear stresses are in the plane of the cross-section - adjacent cross-sections tending to slide over each other. When the body experiences a sideways thrust, as from wind, then a BENDING MOMENT is set up in it. One side of the body is under vertical TENSION and the other side is under vertical COMPRESSION. Brickwork and concrete are much the weakest when under tension. Not so weak when under shear. Much the strongest when under compression. The weight of brickwork exerts a uniform compressive stress over the cross-section. Initially there is no tensile stress. But the bending moment due to wind on ONE side of the structure eventually overcomes the compression. On THAT side the stress becomes tensile and the brickwork parts company with itself, ie., the structure initially fails under tension. It is only AFTER failure has occurred due to tension that shearing takes place and bricks begin to slide sideways, one over the other. The art in the design of brick and concrete structures, eg., as for chimneys, bridges and gravity damns, is NOT to allow any TENSILE stresses to be set up. Hence the frequent use of steel reinforcement. Memo: In view of the variability in such materials apply large factors of safety. ---- Reg, G4FGQ |
"R. Torsten Clay" wrote in message ... This was with a Radio Shack chimney mount. Just the chimney mount by itself was too flimsy. I found that it was necessary to add a set of guys, attached just below the rotator and running to the roof corners. The guys made the whole thing much more secure and took some of the windload off of the chimney. Torsten N4OGW What I did was to use a 10 foot Al pipe, and extend it all the way down to the roof. This was on the inside downslope side of the chimney. I fastened the pipe to the roof with a RS roof mount. This gave me a longer moment arm, and took the vertical weight off the chimney. I have a rotor and 18 el M2 432 antenna on it, about a foot above the rotor. Smaller than a large TV antenna. I would not do remotely what has been suggested here. Tam/WB2TT |
"Richard" wrote in message ... I've no real experience of putting up antennas on the chimney of a house. Obviously, I must not overload the chimney breast. I'm thinking about putting up the following: ______ Discone / | \ __ / || \ A | __ ___|x___ 5 ele.2m yagi | B | | __ |x| 5 ele. marine yagi | | C | | | __ |x| 5 ele. FM yagi. | | D | | __ | / \ Rotator /__\ | | ______ | | | Chimney | | | | | This is too ambitious, I realise that now. I think one 4 or 5 element FM or 2m yagi is about what would be acceptable. And the antenna not far above the rotator. |
Obviously, I must not overload the chimney breast.
Chimneys have surprisingly little structural strength. I'd have more faith in a vent pipe mount. At least the pipe will bend, instead of cracking. |
Hello,
if they do not detune each other, I would love to see the chimney after a gust of wind! "Richard" wrote in message ... I've no real experience of putting up antennas on the chimney of a house. Obviously, I must not overload the chimney breast. I'm thinking about putting up the following: ______ Discone / | \ __ / || \ A | __ ___|x___ 5 ele.2m yagi | B | | __ |x| 5 ele. marine yagi | | C | | | __ |x| 5 ele. FM yagi. | | D | | __ | / \ Rotator /__\ | | ______ | | | Chimney | | | | | I'm wondering about the spacings, A, B, C, and D. A, spacing between bottom of the discone and the boom of 2 m yagi. B, spacing between boom of 2m yagi and boom of marine band yagi. C, spacing between boom of marine band yagi and boom of FM yagi. D, spacing between boom of FM yago and top of rotator. As for the mast, I'm thinking what about 1.5" steel tube. As for rotator. No idea what model I'd need. Any thoughts? Am I trying to be too ambitious? I could leave out the marine yagi if I had to. Thanks. Rich. |
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