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Best low cost intro beam

Discussion in 'CB Antennas' started by lonestarbandit, May 27, 2021.

  1. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    I often think about making one out of copper water pipe tubing soldered together. Just haven't gotten around to it.


     
    #31 Shadetree Mechanic, May 31, 2021
    Last edited: May 31, 2021

  2. barefootindian

    barefootindian Supporting Member

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    How do beams multiply signal power. Some beams are 14 times multiple and others have bigger multiples, being bigger antennas, so how is it done?
     
  3. freecell

    freecell Active Member

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    isotropic (source) radiator

    the point of origin for the purely omnidirectional radiation of electromagnetic energy located at the absolute center of a sphere which radiates energy of equal intensity at all points of the inner surface (effective area) of the sphere. the isotropic radiator exists only in theory since construction is impossible but it is useful as a reference by which to gauge the directivity of electromagnetic radiators.

    the directivity of the isotropic radiator is 0 dB. and the power multiplier ratio is 1.

    from this reference point it is clear that any effort to concentrate or focus the energy produced by the radiator (for example, the addition of a parabolic reflector) in an effort to increase the intensity of the radiation to any fractional area of the internal surface of the sphere will distract from the intensity of the radiation in the direction of large portions of the sphere's internal surface and will produce an increase in directivity in the favored direction relative to the placement of the reflector element with respect to the radiator.

    the antenna does not "multiply" power or signal. the antenna concentrates and focuses energy in a specific direction (azimuthally and / or vertically) at the expense of the loss of radiation intensity in other directions. this is the meaning of the word directivity. this is not automatically translated into "gain" until the radiation efficiency of the antenna has been determined, based primarily upon system values of radiation resistance and loss resistance present at the antenna feedpoint.

    there is no antenna that is 100% efficient and as such any legitimately stated "gain" figure will always be less than the calculated and / or measured directivity.
     
    #33 freecell, Jun 3, 2021
    Last edited: Jun 3, 2021
    tecnicoloco and barefootindian like this.
  4. SIX-SHOOTER

    SIX-SHOOTER Sr. Member

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    I would never install a beam for the 11 meter band on the Horizontal side.It kills all local & mobile signals by about 20 db due to the difference in polarity.A vertical beam works great for Skip since when the signal bounces off of the ionosphere it changes polarity many times.Why limit your signals when you can have both worlds available? I also would avoid the V-Quads like they were the Plague.I had one & I hated it so badly I gave it to a friend who purchased the stacking kit so he could stack it with the one that he had to improve it.He got disgusted with them & threw both of them away because they SUCKED.so badly.We both ways of mounting them & they still were Terrible.My Starduster M-400 & Super Scanner both worked far better than the V-Quads even the stacked ones.

    SIX-SHOOTER
     
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  5. lonestarbandit

    lonestarbandit 4-2-9 Central TX

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    Odd tons of people swear by the V quad as a lightweight small beam. This was the topic after all. Also I have a groundplane so I'm not worried about communicating locally on a beam. They arent really designed for close in local communication.
    Also thanks Freecell for that brain killing yet completely accurate description of how a beam functions. I probably shouldn't have read it right after getting off work no matter how accurate it is lol
     
    #35 lonestarbandit, Jun 3, 2021
    Last edited: Jun 3, 2021
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  6. barefootindian

    barefootindian Supporting Member

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    Thank- you for the explanation freecell. I had to read your post a few times and picture it in my mind to get an understanding of the working of a beam antenna.
    So when the manufacturers state the various power multiplications inherent in their divergent range of beam antennas,that in reality its only an advertising ploy/gimmick to fool the buyer into parting with their hard earned Dollars/Euros/Pounds etc etc yeah?
     
    freecell likes this.
  7. freecell

    freecell Active Member

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    generally speaking, if they state any claim as to the "gain" of the antenna without any statement of radiation efficiency, at the very least they're being disingenuous, not totally forthcoming with regard to the facts.

    here's an example: say they claim a certain antenna has a gain of 5.82 dBi. but the radiation efficiency is only 70%. treat the stated gain as directivity and assume that since no Reff has been given, treat the "gain" figure as such: directivity X radiation efficiency = gain. 5.82 X .70 = 4.074 dBi. (4 dBi.) only when Reff = 100% (not happening) does directivity directly translate to gain.

    here's another example from another well known antenna, the avanti astroplane. advertised at 4.46 dBi. gain with a power multiplier ratio of approximately 2.79X. both of those figures are incorrect if Reff is < 100%. seeing as most of these antennas were incorrectly configured and then mounted on conducting support structures without isolating element #14 (also known as "the mast") which is required to be a half wavelength long at the operating frequency for maximum radiation efficiency, this antenna had a Reff well below 100% and once again, both of these numbers were substantially less than advertised.
     
    #37 freecell, Jun 3, 2021
    Last edited: Jun 4, 2021
    lonestarbandit likes this.
  8. The20poundhammer

    The20poundhammer Sr. Member

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    Well i had a set of stacked V quads back i the late 70's thru the 80's and really liked them. They had some really tight corners and talked great. They were made by Wilson back then dont know if Maco changed them any but mine worked.
     
  9. lonestarbandit

    lonestarbandit 4-2-9 Central TX

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    So I'm betting the 11x of maco vquad is probably about 9x accounting for most the variables?
     
  10. freecell

    freecell Active Member

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    11X is equal to 10.4 dB. of directivity, no telling what they claimed for gain. multiply the amount of tx power actually delivered to the antenna by the power multiplier ratio to get an idea of effective radiated power, less antenna efficiency of course. the v-quad is a fairly efficient antenna.
     
    lonestarbandit likes this.
  11. groundwire

    groundwire Sr. Member

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    If you want to talk to your neighborhood mudducks then by all means mount it vertical. I was assuming the man was a skipshooter so i said horizontal. Local talking, hahahaha.
     
  12. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    Man made noise is vertically polarized, so mounting horizontal takes advantage of this as well as having a better take off angle than vertical. An omni antenna is best for local talk, doesn't make sense to keep moving the beam to get the people around you. If your rotor is big enough, you can mount the omni over the horizontal beam. That's the best of both worlds.
     
  13. HomerBB

    HomerBB Sr. Member

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    For me, 50% of the reason I mounted 11m beams horizontal was to depress local signals in order to better hear dx. The other 50% is because it works better and looks prettier.
     
  14. lonestarbandit

    lonestarbandit 4-2-9 Central TX

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    I cant afford the kind of rotor it would take to spin and indeed take the wind loading of the Imax and a big beam together lol
    A little tv rotor would break. But a separate moxon or vquad it would handle I think.
    I mean who wouldn't want a giant 6 or 8 element its just not practical for me atm.
     
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  15. lonestarbandit

    lonestarbandit 4-2-9 Central TX

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    As of tonight available power should be around 650ish. Depending on drive etc.
    So if I had lets say Vquad ... That's over 7kw directed power equivalent not accounting for efficiency loss I am assuming unless I'm adding the wrong figures. I'm sure I'm mangling terms. Where's Freecell..
     

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