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antenna and height

Discussion in 'CB Antennas' started by BammBamm, Mar 13, 2012.

  1. BammBamm

    BammBamm Well-Known Member

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    I am curious I have a I-max on 2 10' fence poles mounted at 20' to base of antenna. I am moving to a new home and plan to construct the same antenna setup but place the bottom of the mast on my back porch roof and secure it to the peak of the home and where ever else needed to secure it. My porch roof is at 23' and the peak of the house is at 46' so after finding this out I want another 10' pole added to put the base of the I-max at 53' above ground and the mast would only be 7' above the peak of the roof. I see no reason that this is a problem but was wondering how much of an improvement will I see over my setup now at 20' compared to 53'? I know it will be better but by how much? My S-2016 folded over a few days ago in the wind so my I-max is back and seems to be the only antenna able to take the windy city short of $250+.


     
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  2. KC9Q

    KC9Q Supporting Member

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    To get a rough estimate use the formula SQRT(2 x Ant Ht) x 1.15.

    20 ft = SQRT(2 x 20) = 6.245, then 6.245 x 1.15 = 7.27 Miles

    53 ft = SQRT(2 x 53) = 10.3, then 10.3 x 1.15 = 11.84 Mile

    That's an increase of 11.84 - 7.27 = 4.57 or 4.6 Miles roughly.

    If you're on a hill overlooking the area, the range will be greater. As stated before, this is a rough estimate and does not take into account terrain losses which could increase or decrease this estimate.
     
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  3. can you explain your formula and how/where you learned of it ?
    i ask because i talked much farther than 12 miles on a 3 ft little wil 9 ft to the tip .
     
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  4. KC9Q

    KC9Q Supporting Member

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    It's an optical Line-Of-Site formula with 15% Over-The-Horizon factor added used for Two-Way radio calculations. As I said it's only a rough estimate. It would take an extensive propagation program to provide a more accurate answer. As to where it originated: In Antenna Theory 101 in Engineering school. You can also Google the formula.
     
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  5. thanks for the quick reply
     
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  6. KingCobra_CDX882

    KingCobra_CDX882 W9WDX Amateur Radio Club Member

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    Another consideration in height..
    Every time you raise the antenna a full wave length
    (for 11 meters or cb .. that is basically 33 ft per wavelength_

    Originally you had 20 ft hight..
    You can add an additional 33 ft ( or a wavelength for 11 meters)

    You should on receive get at least a Db addition to what you had been receiving (and same for transmitting )...
    but locally.. for skip for transmit or receive you can not know for sure what gain you will have .. Although typically you will naturally get out and hear better when able to raise your antenna higher
     
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  7. GnG8d

    GnG8d Well-Known Member

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    Just get your antenna as high practically possible and don't worry about wavelengths, that's more CB myth. In general, what's good for local is also good for DX by lowering your radiation angle.


    Sent from my iPhone using Tapatalk
     
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  8. Mudfoot

    Mudfoot Supporting Member

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    That formula sounds more for calculating tower to tower positioning.
     
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  9. GnG8d

    GnG8d Well-Known Member

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    BTW, since when did 11m=33'?


    Sent from my iPhone using Tapatalk
     
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  10. Robb

    Robb Yup

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    A Imax 2000 or any 5/8 wave antenna one wave length above the ground yields the avails the lowest angle of radiation to the horizon.
    It also optimizes DX:


    [​IMG]

    Antennas Elevation Angle in Degrees

    Vertical
    1/4 wavelength long 28 (15 - 40)
    3/8 wavelength long 23 (12 - 35)
    1/2 wavelength long 18 (09 - 25)
    5/8 wavelength long 12 (07 - 18)

    Hortizontal Dipole
    1/8 wavelength long above ground 90 (55 for lower 3db point)
    1/4 wavelength long above ground 60 (38 - 82)
    1/2 wavelength long above ground 30 (18 - 40)
    3/4 wavelength long above ground 21 (14 - 28)
    One wavelength long above ground 17 (09 - 19)

    Hortizontal Yagi
    1/4 wavelength long above ground 43 (32 - 54)
    1/2 wavelength long above ground 30 (18 - 38)
    3/4 wavelength long above ground 21 (13 - 28)
    One wavelength long above ground 17 (09 - 18)

    From:
    http://www.worldwidedx.com/general-cb-services-discussion/132925-antenna-height-vs-skip-angles.html
     
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  11. GnG8d

    GnG8d Well-Known Member

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    I agree that raising an antenna will lower the radio angle, but nothing special happens at 36'.




    [​IMG]
     
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  12. hammer0630

    hammer0630 Active Member

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    Damn, I wish I could understand this graph. It looks like some one transmitting at the North Pole and the signal is being sent east against it's will.
     
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  13. W5LZ

    W5LZ Crotchety Old Bastard

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    That formula is close enough for 'LOS' propagation. The thing to remember is that HF, the 11 meter band, is not 'LOS' to start with. The 'radio horizon' isn't the limit for HF.
    How much improvement will be seen by raising/doubling the height of an antenna? If you can ever quantify that for any particular band you could make a fortune. Unfortunately, there's no way to predict that sort of improvement, how much it'd be, just way too many other things affect reception than just antenna height. I think you would be safe in thinking that it would be a noticeable difference. After that, your guess is as good as anyone else's.
    I agree about the 'wave length' theory, don't put much faith in it. If done correctly, an antenna will work okay mounted at ground level. The higher you can go with it (done correctly) the better that "okay" becomes.
    Do it, then you can tell us how much it improved things!
    - 'Doc
     
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  14. hookedon6

    hookedon6 W9WDX Amateur Radio Club Member

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    agreed,............. I have a 6 meter quad on a hazer, and often there is a marked difference when I run it up or down on the electric winch.

    but, thats 6 meters, one of these days I'm gonna put an HF antenna on the hazer and play with it<<More audio>>
     
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  15. Robb

    Robb Yup

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    The DX advantage is optimal when the antenna is brought to one wavelength. However, you get what you pay for in this regard. It has other consequences, as Captain Kilowatt pointed out:

    Sooo - DX 'tuning' depends on what freq is used, type of antenna and its take-off angle, and how high you put it up.
    Food for thought.
     
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    Last edited: Mar 13, 2012

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