Want to put up an antenna on my chimney whe where do I start?

[Falcon4]

Want to put an antenna on my chimney. Looking mostly into airband but I also monitor a P25PII system as well if there is something that c could handle both I would appreciate it. I monitor via RTL-SDR on two different machines.

 

[ka3jjz]

There is no mode-specific antenna - freqs, yes, but not modes. Your first stop - finding out about the NEC code and learning about what is considered to be proper grounding. Doing this now would save you a lot of hassle later. Tons have been written about this subject. Use Google...Mike

 

[jim202]

Well first of all, mounting an antenna on a chimney is asking for an expensive repair job down the road.

Let me explain where I am coming from. Years ago, before cable TV and other means to get a signal, you would see all sorts of antennas on chimneys every where. But the down side of this is the vibration of the antenna mount, along with the wind will cause heavy torsion on the joints between the bricks or cinder blocks to crack over time. This becomes an expensive repair when you find your chimney rocking back and forth.

Even with a flue liner in the chimney, you will have damage given enough time.

You would be much better off using an off set mounting bracket near the peak of the roof. If your roof over hangs the side of the house, then you probably won't fine a bracket long enough to extend over the edge of the roof.

Then maybe a better mount would be a tripod mount on the roof. Just make sure the lag bolts you use go into the roof joists and not just the plywood. Also make sure to use a sealant around the lag bolt hole. You don't want the roof leaking.

Also make sure you ground the antenna after mounting it. Your home owners insurance will require the antenna to be grounded. Use a solid wire from the antenna down to the ground where you drive in an 8 foot ground rod. No sharp bends in the wire. Not sure if the insurance company will spell out the wire size or not. When working for the cellular companies, we used number 2 solid that was plated to reduce corrosion.

It would be wise to use some anti corrosion compound on the grounding joints to keep down oxidation of the grounding connection. I have used Pentrox with very good results. Plus I use it on any threaded hardware to keep it from gauling and seizing up.

Good luck with your installation.

Jim

 

[Groeteschele]

For the love of God don't do it under any circumstances if you still use your chimney. Even if you don't use it anymore the most popular misconception in supposed high wind and extreme weather areas is to not mount large aerials on a chimney but that is not the main danger in the least. Maybe not in America but in Europe countries places very old including chimneys with porous bricks, improper flashing and other issues. The number one danger depending on chimney location on roof is most radio listeners don't think to ground the aerial system and second being not professional aerial installer the average radio guy over tightens the mount to the chimney leading to catastrophic chimney failure over time or even sooner after an extreme weather event. Roof leakage is the most common problem from most chimney mount aerials after being exposed to extensive wind conditions.

 

[a417]

How close to 30 are you? From what I remember of the area, 30 runs right thru a little valley...are you fortunate enough to be up on one of the hills bordering it? You may just need to get outside of your house, and not that far up in the air.

 

[mmckenna]

Depends on chimney construction.
Around here code requires brick/masonry be reinforced. Mine has rebar. It's -very- common around here for TV antennas to be installed on chimney mounts. Even after some -large- earthquakes, there haven't been any issues.
Key is keeping the antenna/mast reasonable. A small VHF/UHF vertical on a short mast properly installed is not going to be an issue with a reinforced chimney.

If there is any question about your chimney having rebar in it, choose a different location. An improperly installed mount with too large an antenna hung off bracket mounts can be just as dangerous.

 

[spongella]

I have had many chimney mounted antennas using wrap-around strap mounts, never had any problems. Always had a discone plus a small TV antenna with masts no longer than 4 feet attached to the chimney. Shied away from larger antennas due to wind loading. Periodic inspection of the chimney exterior every few years is what I do.

 

[Falcon4]

How close to 30 are you? From what I remember of the area, 30 runs right thru a little valley...are you fortunate enough to be up on one of the hills bordering it? You may just need to get outside of your house, and not that far up in the air.

I'm actually on one of the hills but unfortunately one of the smaller ones I have no problem getting the west p25p2 system im just wondering about airband and ads-b. Im debating maybe just trying an antenna in the attic just to start and then if I don't get my desired results trying the roof then....I like the idea of a corner mount as well.

 

[prcguy]

I've used stainless steel strap type chimney mounts and some home made ones since the mid 1970s with absolutely no problems. I've never seen or heard of a chimney problem from using a strap type mount. If you think about the forces it imparts on a typical brick chimney the bricks and mortar can't go anywhere because they are being held together by the straps under tension.

If you were to do something stupid like have the two straps only a foot apart trying to hold up a 20ft mast with a huge antenna, then all bets are off, but a pair of straps 4 or 6ft apart with a reasonable size mast and antenna is absolutely no problem.

 

[a417]

I've used stainless steel strap type chimney mounts and some home made ones since the mid 1970s with absolutely no problems. I've never seen or heard of a chimney problem from using a strap type mount. If you think about the forces it imparts on a typical brick chimney the bricks and mortar can't go anywhere because they are being held together by the straps under tension.

If you were to do something stupid like have the two straps only a foot apart trying to hold up a 20ft mast with a huge antenna, then all bets are off, but a pair of straps 4 or 6ft apart with a reasonable size mast and antenna is absolutely no problem.

Agreed, I put this on a S.E. PA rescue station's chimney to prove a point that their magmount on the AC condenser shell was s**t and the reason their alerting got worse after the county switched from low band to VHF hi-band AND started transmitting off a tower they had line of site with. To appease the B.O.D. (who was family with the local inspector), we put 2" aluminum angle iron 2 feet above & below the strap lines (on each corner) to distribute the forces on the chimney, and the whip height was even with the roof peak...and that was 6 years ago...not a peep. Pretty sure they had roofing work done on the station since then.

if you do it carefully, and don't expect it to hold a Super StationMaster on 20 ft of schedule 80 up to hurricane force winds, I think you'll be ok.

 

[prcguy]

The angle stock is a great idea and I've used that on a huge chimney install in the mid 1970s that held 20ft of heavy wall pipe and a 22ft antenna on top of that. This chimney was made of large cinder blocks and was extremely strong and if anything the steel cable straps with turnbuckles and steel angle stock in each corner added to the strength of the chimney.

Agreed, I put this on a S.E. PA rescue station's chimney to prove a point that their magmount on the AC condenser shell was s**t and the reason their alerting got worse after the county switched from low band to VHF hi-band AND started transmitting off a tower they had line of site with. To appease the B.O.D. (who was family with the local inspector), we put 2" aluminum angle iron 2 feet above & below the strap lines (on each corner) to distribute the forces on the chimney, and the whip height was even with the roof peak...and that was 6 years ago...not a peep. Pretty sure they had roofing work done on the station since then.

if you do it carefully, and don't expect it to hold a Super StationMaster on 20 ft of schedule 80 up to hurricane force winds, I think you'll be ok.

 

[thom]

What about a DPD Omnix, that weighs only 2 lbs, a 5 ft mast with chimney straps? Would that still not be a good idea ?

 

[prcguy]

What frequencies do you want to hear? The Onmi X is good at some, probably not so good at others.

What about a DPD Omnix, that weighs only 2 lbs, a 5 ft mast with chimney straps? Would that still not be a good idea ?

 

[thom]

The Omnix is installed in my attic being used as a backup antenna on my SDS 200 . My main antenna is an older DPD LP mounted on the roof. I thought I'd get the Omnix up there to feed my SDS 100, VHF through 800's. The LP is sufficient for what I listen to, I just thought the Omnix is not doing me much good in the attic. I was wondering if it would put too much stress on the chimney seeing that it weighs only 2 lbs.

 

[a417]

I was wondering if it would put too much stress on the chimney seeing that it weighs only 2 lbs.

2lbs on a 5ft mast secured w/ (assuming) 2 straps to a bricked chimney should be just fine. Much heaver antennae were all the rage back in the day for broadcast TV, and those had much larger wind loading than the Omnix does.

 

[thom]

Thanks for the replies, now all I have to do is decide if I want to climb a ladder or not.

 

[Ubbe]

What about a DPD Omnix, that weighs only 2 lbs, a 5 ft mast with chimney straps? Would that still not be a good idea ?

Its weight are of less importance, it's its wind load that matters, how much drag it has in the wind which increases with the square root of the wind speed. Thice the wind speed gives 4 times the power that tries to drag down the antenna.

/Ubbe