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Dipole directionality

Discussion in 'CB Antennas' started by 918Oklahoma, Dec 30, 2014.

  1. 918Oklahoma

    918Oklahoma
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    KG5FLM

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    I'm experimenting with a 1/2 wave dipole that I have mounted about 25ft up running slightly Southeast-Northwest. I've had the antenna up for about a week and a half now. I can hear quite a bit of skip from around the country, but the only contacts I have made are in New England. Rhode Island, New York, Mass., Connecticut,Pennsylvania. These are the states my antenna loves to talk to.

    So just how directional is a dipole antenna? Some have told me thst my dipole shouldnt be too directional, but it is seeming that way. I feel like i may annoy certain RI stations because its like im pointed right at them lol. I can hear certain stations for long periods of time.


     

  2. camaro1

    camaro1
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    I have always heard that if they are less than 1/2 wavelength above ground they will be fairly Omni directional,, and that the directional will start after you get above the 1/2 wavelength in height
     
  3. vkrules

    vkrules
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    You got it. Even a perfect installation (not many of them in real life) wont be very directive, it"s more about the few degrees of null of the ends rather than directivity .
     
  4. vkrules

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    That perfect example of a dipole in free space has a 3db beamwidth( thats the point at which the signal drops 3db or 1/2 of a s point) of 80 deg Thats off the front and back 160 deg in total and falls off slowly to a 30 -40 db null off the ends. In fact the The -10 db points are only 40 deg wide So out of 360 deg you only have 80 deg where the signal drops 10 db or more.In the real world this is much less .Height above ground, surrounding objects .not using a balun at the feed point, not running the coax at 90 deg away from the feedpoint for 1/2 wave length can all skew the pattern . Simply put it usually fills in some of the null.Low dipoles as mentioned earlier tend to be omni directional
     
  5. 918Oklahoma

    918Oklahoma
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    KG5FLM

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    Just for some background, My dipole has a balun, coax basically drops down at 90 degrees and runs straight into the shack. It is at about 20-25ft above ground so that is slightly higher than a 1/2 wavelength.

    This evening after the
    New England skip started to fade out and i was hearing all over Southern cal, Nevada, Oregon.. but I couldn't get a single QSO with any of them. Usually when i keep hearing strong stations I can get them after enough tries, when they are in the N.E... not the case with the west.

    Could this just be a matter of propagation, even after a week and a half? If given enough time for conditions to change do you all think my dipole will start getting me into other places? Would lowering the antenna make it more omni-directional, in theory?
     
    #5 918Oklahoma, Dec 31, 2014
    Last edited: Dec 31, 2014
  6. tba02

    tba02
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    WOOF

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    Rather than lower it, why not rotate it some and see if anything changes? I don't often hear OK station here in northern California either.
     
  7. Robb

    Robb
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    Yup

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    I think that your dipole setup is near perfect as well.

    Now it might be the right time to build a vertical antenna, get a real antenna switch, another piece of coax, and be able to switch between the two differently polarized antennas.
     
    camaro1 likes this.
  8. Captain Kilowatt

    Captain Kilowatt
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    FINALLY!! SOMEONE THAT UNDERSTANDS!! I have been trying to tell people for years to stop worrying about trying to get the optimum take-off angle for DX and stop worrying about trying to get their target areas in the main lobe of their fixed wire antennas and worry about NOT getting them in their nulls in either the azimuth or elevation angles. The nulls are far more to worry about than the lobes. A lobe may be only 3 or even 6 dB stronger in one area while a null can be 20-30 dB weaker. The pattern of even the best installed dipole is as broad as a barn door and unless it is withing ten degrees or so from directly off the ends than it is essentially omnidirectional.
     
  9. vkrules

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    Rather than lowering your dipole you could try bringing the ends down inverted v fashion that would also make it less directional.As CK said as long as the direction you want isn't straight down the ends it most likely isn't necessary .
     
    KC9Q, Captain Kilowatt and binrat like this.
  10. w9cll

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    I second this.
     
  11. vkrules

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    CK was just thinking of a classic example.Using a 40 meter dipole on 15 meters Most put the dipole up thinking about the direction of the 40 meter lobe Then aren't impressed with the performance on 15 when actually the gain is much higher.The four main lobes are narrow ,and at 45 deg with big nulls in the pattern front and back. Fixed antenna " all about the nulls"
     
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  12. 918Oklahoma

    918Oklahoma
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    Yeah ive thought about doing this, but it would be a lot harder to find somewhere to mount it that would be as high up.

    I think ill keep trying it how it is, then when the weather is a bit more favorable out i will climb the 25ft up into the cedar and move the leg to a different tree to see how it affects things. It just seems like if i could hear the western stations, id be able to contact some of them... Maybe getting the optima mk3 next week will make a difference with that aspect of it.


    Also, the dipole may not be 100% straight. Could a slight elevation change in the height of one of the legs cause it to favor one direction more than the other? And how much does the tightness in the lines affect it?
     
  13. w9cll

    w9cll
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    You could also make another one and put it over the other one facing the other direction. With the use of a switch box would allow switching between them.
     
  14. RatsoW8

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    Your perceived directivity into only one area may is probably just recent propagation and nothing else. Just keep at it, it will change.
     
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  15. DainBramage

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    agreed,....... I think a lot of his "directivity is really his "skip zone".
     

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