Chimney mounted tiltover mast--need a pivot point

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K3RW, Jun 12, 2017.

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  1. K3RW

    K3RW Premium Subscriber QRZ Page

    I'm trying to design a HOA and wife-friendly mast that I can mount on the rear chimney of the house. It is below the roofline and I figure if I can have a mast swing up it could reach a few feet above the roofline with ease, and support a 50-1300mhz log periodic. Reason I'd roof mount it is because the chimney is on the right side of the house, and to the fenceline I wouldn't have enough space to lay one down--and the kids would mess with it (!).

    This is sort of what I'm envisioning:
    [​IMG]
    The chain would keep it down and out of view when not in use and keep it from being vulnerable to some of the high winds we get in late Fall.

    Problem is, I can't seem to find this pivot hinge thing. It seems to be that I just don't know what it is called. I figure I will have to weld one in. It might be something I could make--a pipe that slips tightly into another pipe, and I pound the ends flat to seal it, and put in a grease fitting. But if I could find something off-the-shelf, I'd really rather do that.

    [​IMG]

    Something like this? I couldn't tell if the bearing would actually stay IN. Is there something more suitable?

    If you can imagine a long aluminum pipe--the long part of the mast, and a short pipe, which has the counterweight mounted to it--then the pivot hinge is the part that allows this to tip up smoothly. This wouldn't be drilled into the chimney, but rather secured with heavy strapping--so it doesn't go into the masonry and screw up the chimney.

    What would be great would be something like a parking lot gate arm, automate it, and it goes up and down. That's all I need it to do.

    Any suggestions for this?

    The other potential solution is something like a crankup mast, but it was challenging to envision it being strong enough to hoist an antenna and not flop over. Using a tower frame, its pretty easy--but really heavy, and budget-wise a non-starter. But here's a second design I thought of.
    [​IMG]

    It would be far easier to just mount the antennas on the gable and leave them be. But to not draw ire and for antenna survivability, I'd like something a bit stealthy.

    Any suggestions are truly welcome.
     
  2. KM4JB

    KM4JB XML Subscriber QRZ Page

    That is a great idea. I would just use a "unit hub" from a car. They already have mounting flanges on both sides.

    I have plenty of them laying around that I removed while doing PM's. One from the rear axle of my 1 ton truck would probably support anything you could mount to it.

    I would look for one from the front of a two wheel drive vehicle, doesn't need to be that big to be plenty strong. You just need to know if it needs an axle stub to provide preload on the bearings (basically to hold it together). I know my Jeep fronts do but the one ton rears don't.

    Good luck and thanks for the idea
     
    K3RW likes this.
  3. N8CMQ

    N8CMQ XML Subscriber QRZ Page

    Before mounting it to the chimney, be sure it is strong enough to support the wind load.
    I had a masonry chimney break and fall with a deep fringe tv antenna and rotor mounted with a strap mast mount.
    Nothing was seriously damaged on the house, but the antenna and mast did not fare well.
     
  4. KJ4TX

    KJ4TX Ham Member QRZ Page

    Do a google search on steel pipe mounting flange and see if something like that wouldn't work for you. They come in all sizes and lengths.

    Mike
     
  5. WT4W

    WT4W XML Subscriber QRZ Page

    Yes, I'd be leery of putting any kind of structural load on a chimney.... they just aren't built for that.
     
    KA0GKT and AK5B like this.
  6. KA9UCN

    KA9UCN Ham Member QRZ Page

    KM4JB
    I like the idea of using car hubs but I would choose a rear off of a 4 bolt common Chevy.
    They will take just about anything the elements or antenna load wants to throw. They are sealed units and cheep at the auto parts store and very cheep from a salvage yard.

    Joe KA9UCN
     
  7. AK5B

    AK5B Ham Member QRZ Page

    Put up signs on both sides of the house that read, "BEWARE OF FALLING BRICKS" and take out extra liability insurance as long as you're at it. Chimneys aren't suitable for anything besides venting smoke that I know of.
     
  8. KA0GKT

    KA0GKT Ham Member QRZ Page

    Correct.

    Brick and mortar joints are strong under compression, they aren't strong under shearing loads. In many places, chimney mounted antennas are prohibited by fire codes.
     
  9. N4SRN

    N4SRN Ham Member QRZ Page

    Timely thread. I'm thinking a aluminum mast hinged at a ground-mounted base at the chimney base that is stabilized by a chimney. Perhaps a band around the top with two pullies that let me pivot it off the ground to brace against the chimney. Not quite the same load?

    Bret/N4SRN
     
  10. AK5B

    AK5B Ham Member QRZ Page

    Sounds like a lateral load to me that will put stress at the top or wherever the band is. Plain and simple, you're asking for trouble sooner or later by using a brick and mortar chimney for anything other than it's intended purpose.
     
    K9MRD likes this.

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