OTA Mounts, Towers, Rigging Hardware - Page 116 - Canadian TV, Computing and Home Theatre Forums

roger1818 · 2012-02-12, 04:48 PM

It might be okay, but my question is why not use proper chimney mounts? Which wall mount were you planning on using? Wall mounts are typically long to extend past the eaves, which usually isn't necessary on a chimney.

balm · 2012-02-12, 06:07 PM

Thank you Roger,

The chimeny is NOT brick, I'd prefer not to squeeze the cladding with straps. The chimney is 2x2x3ft (height past roof).

Another idea is to attach a pipe down the side of the chimney box (not supported by any roof).

The wall brackets are standard stand-offs, 2.75" out, fastner holes 6.5" apart.

My original idea was to run a 10ft pipe from the lower to the upper roof (red line), but I dont think its high enough to clear the chimney top.

roger1818 · 2012-02-12, 07:39 PM

In that case, you should be able to use a short (3" or 4") wall mount such as a CM-9025, CM-9023 or CM-3079 (not sure the difference between the last two). Just make sure the lag bolts hit something solid (more than just plywood).

One other thing, I noticed the forum sponsor says the brackets should be at least 20% of the mast length apart. This seems too close together to me. I would think 1/3 (33%) would be a better ratio, but it really depends on the size (wind load) of antenna being installed.

balm · 2012-02-12, 07:43 PM

yes, I wanted to use them, but the chimney being about 36" high, puts the brackets at about 30" separation (if I want the pipe resting on the upper roof where the chimney first goes thru the roof), leaving about 90" above the top bracket unsupported

I think the upper bracket force in that case is about 3-4 x the wind force on the antenna !

roger1818 · 2012-02-14, 09:18 AM

balm,

Thinking more about it, IMHO, your best bets would be to either go with your original idea and run a mast from the lower to upper roof. I am not sure how far apart they are at the peek of the upper roof, but it looks like you should be able to handle at least a 15 foot mast, which should be long enough to clear the chimney. I would use a swivel mount (such as the CM-3078) at the bottom, to attach it to the lower roof and a 3" wall bracket at the peak of the upper roof.

The other idea of running a mast down the side of the chimney box, down to the ground is also a good one. I read somewhere that you can get away with only one mounting bracket (at the top) this way by burying the mast about 1.5 to 2 feet, but I would be tempted to put a bracket every 10 feet (at each joint) plus one at the top of the chimney box to ensure the mast doesn't buckle. I would also make sure the mast is sitting on something solid that won't sink into the ground (a paving stone or cinder block might work well).

balm · 2012-02-14, 09:31 AM

Quote:

I would use a swivel mount (such as the CM-3078) at the bottom, to attach it to the lower roof and a 3" wall bracket at the peak of the upper roof.

yes, this is what im doing, but the chimney including the upper metal pipe is about 5 ft above roof, thus to avoid the chimney blocking the signal, I need to go at least 2 ft above the pipe with bottom of antenna. Add another 3 ft to go to top clamp of CM4228HD. So thats at least 10 ft above the roof.

If I only have about 3-4 ft between roofs, & a 13-14 ft pipe, Im not sure thats strong enough. I calculate 3/14=21% using bracket spacing.

Unfortunately the channels are received in the direcetion with antenna facing that chimney...

mrvanwinkles · 2012-02-14, 11:39 AM

Mapmaker, post # 1724

Quote:

Originally Posted by Mapmaker

I have NEVER seen anyone be able to pound one of those Post Spikes into any exact location they wanted them.

Yes, you are exactly correct - this is one of my main installation concerns.

I expect to have some "difficulties" with this.

My my "no concrete" idea goes something like this:

I will have to dig a partial hole to get the tower out and up ...
(done that before ... )

I will be left with three alignment holes deeper down in the earth where the buried tower tips were pulled out. I will deepen these a little if necessary as pilot holes - by tapping down some solid steel rod & removing it.

Then I will carefully tap down bottom tips of the Post spikes into those three pilot holes - aligning them best I can.

Should be able to tap the post spikes back and forth sideways (or up and down) a little for adjustment at the top (with a short cut off piece of 4x4 inserted).

They will not be completely pounded in ... not full length of spike ... with this method - and so, should be more easily "adjusted".

Get tower base inserted and assembled - now it's aligned for sure ...same exact position as before.

Back fill hole with earth around post spikes with earth from earlier DIG. Tamp down earth solid. Wet earth a little and tamp down earth solid again all around. It'll settle solid with time.

[ The concrete solution would definitely have all assembled in place and staked solid in perfect position before pouring concrete ]

Important point:
This is a BRACKET tower with a strong BRACKET high up on the peak of a 2 storey house. So base pins support mostly a vertical up and down load / get a large leverage on sideways loads. Should be no problem with three post spikes like that ...

But I would prefer to do this, in this case, without needing a concrete base.
(for a few reasons)

This BRACKET tower should "FLOAT" solid and secure enough in the EARTH alone, with the downward weight of the tower ... I am hoping ... and settle nice and secure in position over time.
[Just like it did before - with just the tower base alone, buried a couple feet.]

Lowering was done last time with a long, strong rope from the ground ... looped through the bracket at the roof peak, and tied to the tower. Undo the U-bolts on the bracket ... feed rope in slowly ...as it tilts down.

I have a strong pulley with bearings assembly ... and am thinking about a steel cable and hand winch / crank maybe.

The tower is planned to tilt away from the side of the house at a shallow bit of an angle.

Call me crazy ... but I think this will work .

roger1818 · 2012-02-14, 12:43 PM

balm, If it is only 3-4 feet between roofs then you are probably correct. I would then recommend the other option of running it down the chimney box to the ground.

Techno_Dweeb · 2012-02-16, 05:45 PM

I did this quick chimney mount for under $10. A piece of 1-1/2 ABS drain pipe, and 2 clamps for chain link fencing. Fastened with 2 TapCon screws to the bricks. Nice

Click to view larger image...

roger1818 · 2012-02-16, 06:33 PM

Techno_Dweeb, my only concern with bolting to the bricks is the wind force could work the the bricks loose. That is why most chimney kits use straps to wrap around the chimney to distribute the forces across multiple bricks and hold things together. Having said that, your mast is short so the forces should be reasonably small.

Also, PVC pipe isn't the strongest material in the world (I would normally recommend galvanized steel), but once again the mast is short so it should be okay.

Disclaimer: Notice I used the words should in both cases. I haven't done the math to confirm that it is okay so treat my post as a warning of potential failure, not an acceptance of your install.

Techno_Dweeb · 2012-02-16, 06:45 PM

Thanks for the tips. It is fairly sturdy in the wind. I wouldn't try a tall mast with this arrangement, but I did not need any more height so it worked out great. I get solid signal levels on all channels!

Jase88 · 2012-02-17, 07:51 PM

It appears to me from the photo that only two bolts hold the installation (one bottom and another at top). If this is the case, I don't recommend such an install.

Eventually wind load and weight from snow and ice on the antenna will work forces on the bolts. This will eventually wear down the brick in the bolt holes, allowing moisture into the brick. And once it freezes, the brick will fail.

You generally want at least 2 bolts per mount to cancel out such forces.

Otherwise, your install looks good and clean.

BOUVAL · 2012-02-17, 10:56 PM

Quote:

the antenna will work forces on the bolts

Exactly, when there will be ice on the antenna and wind from behind it, there will be some lever effect.

The antenna and the u-bolt should be centered on that ABS drain pipe or even placed near the bottom bolt.
.

balm · 2012-02-22, 09:59 PM

how long a mast pipe can i use in a 3 ft tripod, to hold a CM4228HD, or how high above the top of the tri-pod can the mast be (1.25" dia. EMT mast) ?

thanks

roger1818 · 2012-02-23, 10:26 AM

The rule of thumb is 1/3 of the mast must be between the top and bottom mounts, so if the 3 ft of the mast is "inside" the tripod, then that means you can use a 9 ft mast (6ft above tripod). You should be able to round that up to a 10 mast ft without any problems though as it is just a rule of thumb.

2012-02-12, 04:48 PM	#1726
roger1818 Veteran Join Date: Apr 2006 Location: Ottawa (Stittsville), ON, OTA (Radio Shack Omnidirectional Antenna and 5Y6S in Attic), MythTV HTPC Posts: 5,626	It might be okay, but my question is why not use proper chimney mounts? Which wall mount were you planning on using? Wall mounts are typically long to extend past the eaves, which usually isn't necessary on a chimney. __________________ Link to my TVFool results is in my profile Homepage URL. I suggest others do the same.

2012-02-12, 07:39 PM	#1728
roger1818 Veteran Join Date: Apr 2006 Location: Ottawa (Stittsville), ON, OTA (Radio Shack Omnidirectional Antenna and 5Y6S in Attic), MythTV HTPC Posts: 5,626	In that case, you should be able to use a short (3" or 4") wall mount such as a CM-9025, CM-9023 or CM-3079 (not sure the difference between the last two). Just make sure the lag bolts hit something solid (more than just plywood). One other thing, I noticed the forum sponsor says the brackets should be at least 20% of the mast length apart. This seems too close together to me. I would think 1/3 (33%) would be a better ratio, but it really depends on the size (wind load) of antenna being installed. __________________ Link to my TVFool results is in my profile Homepage URL. I suggest others do the same.

2012-02-14, 09:18 AM	#1730
roger1818 Veteran Join Date: Apr 2006 Location: Ottawa (Stittsville), ON, OTA (Radio Shack Omnidirectional Antenna and 5Y6S in Attic), MythTV HTPC Posts: 5,626	balm, Thinking more about it, IMHO, your best bets would be to either go with your original idea and run a mast from the lower to upper roof. I am not sure how far apart they are at the peek of the upper roof, but it looks like you should be able to handle at least a 15 foot mast, which should be long enough to clear the chimney. I would use a swivel mount (such as the CM-3078) at the bottom, to attach it to the lower roof and a 3" wall bracket at the peak of the upper roof. The other idea of running a mast down the side of the chimney box, down to the ground is also a good one. I read somewhere that you can get away with only one mounting bracket (at the top) this way by burying the mast about 1.5 to 2 feet, but I would be tempted to put a bracket every 10 feet (at each joint) plus one at the top of the chimney box to ensure the mast doesn't buckle. I would also make sure the mast is sitting on something solid that won't sink into the ground (a paving stone or cinder block might work well). __________________ Link to my TVFool results is in my profile Homepage URL. I suggest others do the same.

2012-02-14, 12:43 PM	#1733
roger1818 Veteran Join Date: Apr 2006 Location: Ottawa (Stittsville), ON, OTA (Radio Shack Omnidirectional Antenna and 5Y6S in Attic), MythTV HTPC Posts: 5,626	balm, If it is only 3-4 feet between roofs then you are probably correct. I would then recommend the other option of running it down the chimney box to the ground. __________________ Link to my TVFool results is in my profile Homepage URL. I suggest others do the same.

2012-02-16, 05:45 PM	#1734
Techno_Dweeb Join Date: Apr 2008 Location: Ottawa South Keys - Attic Log Periodic>CF, 4bay Clone>HC Posts: 39	I Like Simple Mounts (And Cheap !!!) I did this quick chimney mount for under $10. A piece of 1-1/2 ABS drain pipe, and 2 clamps for chain link fencing. Fastened with 2 TapCon screws to the bricks. Nice Click to view larger image...

2012-02-12, 06:07 PM	#1727
balm Veteran Join Date: Jan 2009 Location: Montreal Posts: 2,248	Thank you Roger, The chimeny is NOT brick, I'd prefer not to squeeze the cladding with straps. The chimney is 2x2x3ft (height past roof). Another idea is to attach a pipe down the side of the chimney box (not supported by any roof). The wall brackets are standard stand-offs, 2.75" out, fastner holes 6.5" apart. My original idea was to run a 10ft pipe from the lower to the upper roof (red line), but I dont think its high enough to clear the chimney top.

2012-02-12, 07:43 PM	#1729
balm Veteran Join Date: Jan 2009 Location: Montreal Posts: 2,248	yes, I wanted to use them, but the chimney being about 36" high, puts the brackets at about 30" separation (if I want the pipe resting on the upper roof where the chimney first goes thru the roof), leaving about 90" above the top bracket unsupported I think the upper bracket force in that case is about 3-4 x the wind force on the antenna !

2012-02-16, 06:33 PM	#1735
roger1818 Veteran Join Date: Apr 2006 Location: Ottawa (Stittsville), ON, OTA (Radio Shack Omnidirectional Antenna and 5Y6S in Attic), MythTV HTPC Posts: 5,626	Techno_Dweeb, my only concern with bolting to the bricks is the wind force could work the the bricks loose. That is why most chimney kits use straps to wrap around the chimney to distribute the forces across multiple bricks and hold things together. Having said that, your mast is short so the forces should be reasonably small. Also, PVC pipe isn't the strongest material in the world (I would normally recommend galvanized steel), but once again the mast is short so it should be okay. Disclaimer: Notice I used the words should in both cases. I haven't done the math to confirm that it is okay so treat my post as a warning of potential failure, not an acceptance of your install. __________________ Link to my TVFool results is in my profile Homepage URL. I suggest others do the same.

2012-02-16, 06:45 PM	#1736
Techno_Dweeb Join Date: Apr 2008 Location: Ottawa South Keys - Attic Log Periodic>CF, 4bay Clone>HC Posts: 39	Thanks for the tips. It is fairly sturdy in the wind. I wouldn't try a tall mast with this arrangement, but I did not need any more height so it worked out great. I get solid signal levels on all channels!

2012-02-17, 07:51 PM	#1737
Jase88 Moderator Join Date: Jan 2009 Location: Kitchener, ON Posts: 4,109	It appears to me from the photo that only two bolts hold the installation (one bottom and another at top). If this is the case, I don't recommend such an install. Eventually wind load and weight from snow and ice on the antenna will work forces on the bolts. This will eventually wear down the brick in the bolt holes, allowing moisture into the brick. And once it freezes, the brick will fail. You generally want at least 2 bolts per mount to cancel out such forces. Otherwise, your install looks good and clean. __________________ DMX 68' tower, HyGain HAM 5 rotator, Antennas Direct 91-XG & C5, Channel Master 7777 preamp, Siemens surge protection

2012-02-22, 09:59 PM	#1739
balm Veteran Join Date: Jan 2009 Location: Montreal Posts: 2,248	tripod how long a mast pipe can i use in a 3 ft tripod, to hold a CM4228HD, or how high above the top of the tri-pod can the mast be (1.25" dia. EMT mast) ? thanks

2012-02-23, 10:26 AM	#1740
roger1818 Veteran Join Date: Apr 2006 Location: Ottawa (Stittsville), ON, OTA (Radio Shack Omnidirectional Antenna and 5Y6S in Attic), MythTV HTPC Posts: 5,626	The rule of thumb is 1/3 of the mast must be between the top and bottom mounts, so if the 3 ft of the mast is "inside" the tripod, then that means you can use a 9 ft mast (6ft above tripod). You should be able to round that up to a 10 mast ft without any problems though as it is just a rule of thumb. __________________ Link to my TVFool results is in my profile Homepage URL. I suggest others do the same.

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