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Antenna Height

Discussion in 'Local Reception' started by ESA1178, Sep 12, 2012.

  1. ESA1178

    ESA1178 AllStar

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    Dec 3, 2011
    I have a ranch home (single level). However I live in Sacramento Valley.
    It's hard to pick up anything 30 miles away because of the hills, etc.
    I just installed a DB8 Antenna, along with an amp.
    I would like to install it on the roof. I know the higher is better, But I'd like to get away from installing a tripod on my nice new roof. I will be attaching the mast to a chimney with straps.
    My question is: Will a 10' mast be enough? I will probably use a 10' x 1" piece of EMT.


    Thanks!

    Mark
     
  2. Davenlr

    Davenlr Geek til I die

    9,136
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    Sep 16, 2006
    Most TV antennas are designed for 1.25" masts, but 10' would be the most you want on a chimney mount, especially if you have high winds in the area.

    While very much more expensive, a 30' Rohn tower is a good choice for getting it up there a little farther without damaging the house.
     
  3. harsh

    harsh Beware the Attack Basset

    21,192
    182
    Jun 14, 2003
    Salem, OR
    Whatever it takes to get a line-of-sight towards the towers. I'm not a big fan of EMT (1/16" wall) but it is better than the 16ga tubes that they sell on eBay.

    Make sure you don't crush the tubing as it will weaken it significantly.

    I think you'd be surprised what kind of a wind catcher those oven racks are.
     
  4. jimmie57

    jimmie57 Hall Of Fame

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    Jun 26, 2010
    Texas City, TX
    This web site shows the antenna and all the specs with it.
    It shows an antenna mast extension as being 1.5" diameter.
    It also shows that it picks up channels 14 thru 69. Do you have locals like I do here south of Houston, TX like 2, 8, 11, 13 ? You might want to chack on this.

    http://www.antennasdirect.com/store/DB8_HD_Antenna.html

    I used to use the top rail of a cyclone fence as a pole. I do not know what size it is at the moment but it is a lot heavier than EMT and it is also galvanized to keep it from rusting.
    Edit: The fence top rail I found at Home Depot is 1-3/8" dia , 12 gage ( about 1/8" wall ) and 10-1/2 feet long.
     
  5. ESA1178

    ESA1178 AllStar

    51
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    Dec 3, 2011
    I'm considering strapping to a chimney that we don't use.
    This is the EMT I am using:

    "The Allied Tube & Conduit 1 in. x 10 ft. Electric Metallic Tube Conduit offers protection from magnetic fields, impact damage and crushing when pulling electrical cable. This steel conduit resists flattening, kinking and splitting and is coated with zinc for corrosion- and abrasion resistance."


    Is it true that UHF antennas are 'line of sight" ?

    Mark
     
  6. harsh

    harsh Beware the Attack Basset

    21,192
    182
    Jun 14, 2003
    Salem, OR
    1" EMT has an even thinner wall than 1-1/4" EMT. 1" EMT is only 3/64" wall and 1.163" OD. It isn't nearly as resistant to twisting as 1-1/4" at 1.510". You don't want the antenna doing a "parade wave" in a good breeze.

    Technically you don't need to be able to see the lights on the towers, but even leaves will negatively impact UHF. The clearer the shot you have, the less you're going to have to worry.

    As jimmy57 points out, you need to consider whether the antenna is going to perform well (or whether it even matters) for your PBS station being at VHF 9.
     
  7. kc1ih

    kc1ih Legend

    272
    1
    May 22, 2004
    Salem, NH
    Those are the “virtual“ or “mapped” channel numbers, you need to know the actual RF channel numbers, which are usually different, to answer that one.
     
  8. ESA1178

    ESA1178 AllStar

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    0
    Dec 3, 2011
    Thanks for all you responses.
    My next door neighbor took down his 20' telescopic mast a few years back,
    and wasn't using it. He gave it to me for free. I just rescanned my channels and get 40 now, and that's not with the mast!

    Will keep you all posted!


    Mark
     
  9. Davenlr

    Davenlr Geek til I die

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    Sep 16, 2006
    Sounds like you are well on your way to free TV. Have fun.
     
  10. ESA1178

    ESA1178 AllStar

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    Dec 3, 2011
    Morning everyone!

    The mast is a 20' telescope from Rohn. I am considering installing a Channel Master CM 3092 3 ft Tripod Mount. Since I don't have a long boom antenna but a DB8 instead. It should be fine, right? With guy wires of course.. :)


    Mark
     
  11. harsh

    harsh Beware the Attack Basset

    21,192
    182
    Jun 14, 2003
    Salem, OR
    Telescoping masts often don't work all that well with guy-wires unless you freeze the sections. Depending on where you attach the wires, it may just work the mast down and allow it to tilt. It is probably best to have some sort of solid base and skip the wires.

    I'm not convinced that it is reasonable to assume that a bowtie array is necessarily going to create less of a wind load than a Yagi-Uda. Wind is all about cross section, not weight or depth.

    Understand that many of the theories I've presented are not the result of exhaustive testing but based in rudimentary aerodynamic theory.
     
  12. jimmie57

    jimmie57 Hall Of Fame

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    Jun 26, 2010
    Texas City, TX

    I hate to see you bolt this down to your roof.
    I mentioned before that I used the top rail tubing for chain link fencing for mine.
    They can be connected together using a coupling made for that purpose. Some have one end reduced so that it slides into the next piece of tubing.

    What I did was got to the highest point of my roof ( my roof is an A style roof ) and pushed about 18" of the 2 lengths of the tubing
    into the ground with the pole straight up and next to the house.
    Then I used a bracket made for holding antennas to the side of the house and bolted it to the fascia board of the house. I did not have any wires attached to mine and it was a total of about 18 feet in the air when it was all installed.

    If you go with the tripod, make sure you put that roofing tar stuff under the feet and then all around them and even on top of the bolts / screws that you use to fasten it down to the roof so that it does not leak into your ceiling.
     
  13. ESA1178

    ESA1178 AllStar

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    Dec 3, 2011
    So have the mast up and facing W/SW.
    Getting alot of channels. But I know I can get more.
    There is a tree in the way of direct line of sight.
    Thankfully its in my yard and needs trimming down.
    The antenna is at around 20' with an additional house height of 15'. So really at 35'.
    I was considering adding an additional 10' section to 'see' over the tree, but that would be a pain to install.
    So I am going to leave it as a 20' telescopic with the tree trimmed.
    Will keep you posted...

    Mark
     
  14. ESA1178

    ESA1178 AllStar

    51
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    Dec 3, 2011
    OK..
    The tree is too much of an issue right now.
    Major branches on my side close to a power line, and also on the neighbors side.
    I have lost channels, and I attribute that to the tree.
    So, my question of the day is this:

    Are Antenna mast sections unique?
    That is, I have 2 10' ROHN sections.
    But I would like to add another 10' section.
    Will a Channel Master section fit into a ROHN?
    Or a 10' ROHN section fit into a channel master 20' telescopic?

    Thanks!

    Mark
     

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