Chimney Mounting

[Mork]

My chimney is brick, about 22 years old and in good shape. I currently have an R/S heavy duty chimney mount (metal straps, racket tightened),a 5' 14g mast section, small TV rotor with a 5' 14g section atop it. There is a Scantenna LP beam and a ST-2 (omni)currently on it.

My goal is to have one devoted 800 yagi (12 el)(AR2 800 preamp T biased), 1 450 yagi (3el), the general coverage Scantenna LP(AR2 wide band preamp T-biased),and a VHF omni gain (GAM TG5s) and possible an Austin Ferret (AR2 wideband preamp). The beams should point in the same direction,the rotor can handle the wind load. I don't have the chimney dimensions. It is a 2 flue - only one of which is used as we don't use our fireplace. I use Commscope LMR400 equivalent to Stridsberg amp'd multicouplers.

Can this be done with 2 chimney mounts? While I'd like to tower mount most of this, the tower is 200' ft from the shack, so NG.

doc

BTW the pre-amps are appropriate given my low noise level, no intermod, and distance to cell towers etc

 

[kb2vxa]

I don't like chimney mounts for several reasons.

Chimneys aren't as strong as they look, I've seen new masonry crack and separate given the right angular stresses.

Flue gasses cause problems, gas furnace exhaust is heavily moisture laden and water can get into the electrics easily, especially in cool weather. Rain is less of a problem, liquid water has a much higher density than vapor. Oil burner exhaust is highly corrosive and laden with soot, add moisture and you have sulfuric acid laden with conductive carbon particles. Metal, aluminium in particular won't last long in that environment.

These days everything being cheapo cheapo the mounts don't hold up anywhere near as well as they used to especially when you put more than a single small TV antenna on them. The stainless steel bands are of a lower grade, tend to stretch and loosen, I've had a few thoroughly aggrivating installations where I ran out of thread on the retainer bolts and resorted to shims that ended up falling out. Talk about your classic FAIL! In other instances I had the brackets bend in the wind, top one go this way and bottom go the other, classic leaning tower of pizza.

Heavy duty? What a laugh! BTW wall brackets aren't what they used to be either but you might still find a strong eve mount around somewhere and then there is the mother of all mounts, the tripod. When done right they'll stand up to anything nature can throw at them that doesn't rip the roof out from under them.

"While I'd like to tower mount most of this, the tower is 200' ft from the shack, so NG."
Mohammad couldn't make the tower to come to the shack so he brought the shack to the tower and the mountain was moved.

 

[zz0468]

While I'd like to tower mount most of this, the tower is 200' ft from the shack, so NG.

Why not? If you're running decent preamps, 200' of coax shouldn't be a problem, if you do it right.

Warren is right. Chimney mount antennas, especially that many, are just a bad idea.

 

[Mork]

well

200' to the tower, 80' up the tower, 75' from the entry to the shack to the radios... too much loss even with LMR400. Not worth it to me, and not the question I asked.

 

[zz0468]

200' to the tower, 80' up the tower, 75' from the entry to the shack to the radios... too much loss even with LMR400.

About 14 db loss at 900 MHz. Sounds like a lot, but with a carefully designed preamp system at the antenna end, you wouldn't notice the loss. But I understand you're reluctance.

Not worth it to me, and not the question I asked.

No, but you made that part of your question, so it became part of my answer.

 

[jackj]

Damn Warren, are you shunt feeding that tower on 160? I got to say that your shack looks very nice.

Stay away from chimney mounts, they are bad news for a lot of reasons. I don't think what you want to do will last very long, and I don't think your chimney will last long if you try it anyway. Chimneys are constructed a lot of different ways and some are stronger than others. But none are really designed to withstand the side loads and twists that large wind loads will place on them. Do as Warren suggests and either erect a tower next to your house or use a tripod style roof mount. Channel Master and Wineguard both used to sell a very nice tripod for a reasonable price, don't use the ones that RS sells. I've installed quite of few of them in my younger days and they are the way to go for light wind loads.

 

[kb2vxa]

Not mine Jack, that's the "Cottage of Wattage" at K2PG. K2PG: Vintage AM Radio and Other Delights Being familiar with his station in West Creek, New Jersey I can tell you a bit about the towers which not only support antennas but as you noticed are antennas themselves.

Note the skirt wires, the towers aren't shunt fed but rather half wave radiators of the grounded, folded unipole design. Look at it this way, it's half of a folded dipole with the far end grounded, physically a tad shorter than a quarter wave tall. The wires run up the legs spaced out about 15" on PVC pipes, commoned at top and bottom by copper rings, connected to the tower at the top and fed at the bottom through a tuning unit shown in the picture. Being an electrical half wave this puts the 90 degree (current) point at the top rather than the bottom as in a quarter wave giving a low vertical takeoff angle great for DX at night and extended daytime coverage. They're fairly common AM broadcast antennas being extended daytime coverage means a larger market share and increased revenue, not to mention it's a great cheap and dirty way to save expensive steel over even a quarter wave, not to mention a full half wave tower.

So how did he come up with this design? Heh, Phil has been an engineer for many years and is presently working for a broadcast group in Scranton, Pennsylvania. Check out the web site, he's one of those AM Gangstas that give meaning to the term Heavy Metal. Usually when a ham repairs his boat anchor radio he takes the cover off and works from the outside, I had the dubious honor of repairing his Collins 20V from the inside.

To borrow an appropriate signature tag line; "12V radios are for wimps, real radios can kill you."

We now return you to our regularly scheduled discussion of fallen masonry, twisted metal and dead copper spiders but first for your listening enjoyment...
YouTube - The Chimney Song Bob Rivers Comedy Corp
...and one for the old fart's nostalgia..
YouTube - Dick Van Dyke - Chim Chim Cher-ee 1,12 min

 

[SCPD]

Chimney mounts

KB2VXA is right, chimney mounts are also not my preferred method for putting up 'tennas.

But if you got your heart set on it, first go get an old bed frame(a great source for cheap angle iron). Cut it up and put the angle iron behind the straps on all four corners of the chimney. Don't let those chimney mount bands dig into the brick and mortar directly. By making the angle iron almost as long as the chimney, and spacing the mounts wide apart, you are distributing the stress more evenly across the whole chimney, instead of having all the stress only at where the metal bands would be pressing directly against the chimney.